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'''Obesity''' is the medical condition associated with excessive stores of body fat, to the extent that it causes serious health concerns. Obesity is a major problem in today’s society, with over 1 billion people being classed as obese worldwide.
'''Obesity''' is the medical condition associated with excessive stores of [[adipocyte|body fat]], to the extent that it causes serious health risks. Physical problems include [[hypertension|high blood pressure]], heart disease, some cancers and [[Diabetes mellitus type 2]];  emotional problems include low self esteem, and depression.  More than a billion people are classed as obese worldwide, and by 2025, 300 million people are expected to suffer from [[Diabesity|obesity-related diabetes]].


Obesity is an increase in adipose tissue, so much so that it can cause a variety of adverse health consequences. These include many emotional and physical problems. For example, emotional problems include feelings of inferiority, low self esteem, and often in children, and bullying from classmates. Physical problems include [[hypertension|high blood pressure]], heart disease, some cancers and  [[Diabetes mellitus type 2]] which is where the body no longer responds to [[insulin]] and so cannot control its blood sugar levels. By 2025 300 million people are expected to suffer from obesity-related diabetes.
There are many ways of measuring body fat, but the most common  measures the relationship between weight and height by the [[body mass index]] (BMI). A BMI of 30 or more puts you in the category of ''obese''.  This method is simple, but imprecise; people with well-developed muscle may have a high BMI yet a low proportion of body fat.
 
There are many methods of measuring body fat but the most popular method is using the [[body mass index]] (BMI) which measures the relationship between your weight and height. A measure of 30 or more puts you in the category of obese.  This method is simple, but is inevitably imprecise; people carrying a lot of muscle will not receive an accurate BMI measure due to muscle being heavier than fat.


==Prevalence and epidemiology==
==Prevalence and epidemiology==
Obesity is increasing in Europe.<ref name="pmid19286092">{{cite journal |author=Kotseva K ''et al.''|title=Cardiovascular prevention guidelines in daily practice: a comparison of EUROASPIRE I, II, and III surveys in eight European countries |journal=Lancet |volume=373 |pages=929–40 |year=2009 |pmid=19286092 |doi=10.1016/S0140-6736(09)60330-5 |url=http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(09)60330-5 |issn=}}</ref>
Obesity is increasing in Europe.<ref name="pmid19286092">{{cite journal |author=Kotseva K ''et al.''|title=Cardiovascular prevention guidelines in daily practice: a comparison of EUROASPIRE I, II, and III surveys in eight European countries |journal=Lancet |volume=373 |pages=929–40 |year=2009 |pmid=19286092 |url=http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(09)60330-5}}</ref> In the U.S.A., obesity is increased through 2004<ref name="pmid16595758">{{cite journal |author=Ogden CL ''et al.''|title=Prevalence of overweight and obesity in the United States, 1999-2004 |journal=JAMA |volume=295 |pages=1549–55 |year=2006 |pmid=16595758 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=16595758}}</ref> but has been stable since<ref name="pmid18505949">{{cite journal |author=Ogden CL ''et al.'' |title=High body mass index for age among US children and adolescents, 2003-2006 |journal=JAMA |volume=299  |pages=2401–5 |year=2008|pmid=18505949 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=18505949}}</ref>. Among immigrants, the incidence of obesity increases with the duration of living in the U.S.A..<ref name="pmid15598917">{{cite journal |author=Goel MS ''et al.'' |title=Obesity among US immigrant subgroups by duration of residence |journal=JAMA |volume=292|pages=2860–7 |year=2004 |pmid=15598917|url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=15598917}}</ref>
 
In the United States, obesity is increased through 2004<ref name="pmid16595758">{{cite journal |author=Ogden CL ''et al.''|title=Prevalence of overweight and obesity in the United States, 1999-2004 |journal=JAMA |volume=295 |issue=13 |pages=1549–55 |year=2006 |month=April |pmid=16595758 |doi=10.1001/jama.295.13.1549 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=16595758 |issn=}}</ref> but has been stable since<ref name="pmid18505949">{{cite journal |author=Ogden CL ''et al.'' |title=High body mass index for age among US children and adolescents, 2003-2006 |journal=JAMA |volume=299  |pages=2401–5 |year=2008 |month=May |pmid=18505949 |doi=10.1001/jama.299.20.2401 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=18505949 |issn=}}</ref>. Among immigrants, the incidence of obesity increases with the duration of living in the United States.<ref name="pmid15598917">{{cite journal |author=Goel MS ''et al.'' |title=Obesity among US immigrant subgroups by duration of residence |journal=JAMA |volume=292 |pages=2860–7 |year=2004 |month=December |pmid=15598917 |doi=10.1001/jama.292.23.2860 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=15598917 |issn=}}</ref>
 
 


==Causes/etiology==
==Causes/etiology==
Obesity is caused by a mix of environmental and genetic factors.<ref name="pmid2336075">{{cite journal |author=Stunkard AJ ''et al.''|title=The body-mass index of twins who have been reared apart |journal=N a J Med |volume=322 |pages=1483–7 |year=1990 |pmid=2336075 |doi=}}</ref><ref name="pmid17652652">{{cite journal |author=Christakis NA, Fowler JH |title=The spread of obesity in a large social network over 32 years |journal=N Engl J Med |volume=357 | |pages=370–9 |year=2007 |pmid=17652652 |doi=10.1056/NEJMsa066082}}</ref>
Anxiety and depression may lead to obesity.<ref name="pmid19808765">{{cite journal| author=Kivimäki M ''et al.''| title=Common mental disorder and obesity: insight from four repeat measures over 19 years: prospective Whitehall II cohort study. | journal=BMJ | year= 2009 | volume= 339  | pages= b3765 | pmid=19808765
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=19808765 | doi=10.1136/bmj.b3765 }} <!--Formatted by http://sumsearch.uthscsa.edu/cite/--></ref>
===Genetics===
'' See [[Genetics of obesity]]''  
'' See [[Genetics of obesity]]''  


In only very few cases can obesity in humans be attributed to a single gene defect, but many genes have been found that have variants associated with an increased risk of obesity. One of the few genes that variants in the human population associated with increased risk of obesity is the gene for the melanocortin 4 receptor (MC4R). This receptor is expressed in the [[hypothalamus]], and mediates the actions of alpha melanocyte stimulating hormone, a [[peptide]] released by a subpopulation of neurons in the [[arcuate nucleus]] in response to [[leptin]]. <ref name="pmid12646665">{{cite journal |author=Farooqi IS ''et al.''|title=Clinical spectrum of obesity and mutations in the melanocortin 4 receptor gene |journal=N Engl J Med |volume=348 |pages=1085–95 |year=2003 |pmid=12646665 |doi=10.1056/NEJMoa022050}}</ref>
The proximate cause of obesity is a mix of environmental and genetic factors.<ref name="pmid2336075">{{cite journal |author=Stunkard AJ ''et al.''|title=The body-mass index of twins who have been reared apart |journal=N Eng J Med |volume=322 |pages=1483–7 |year=1990 |pmid=2336075}}</ref><ref name="pmid17652652">{{cite journal |author=Christakis NA, Fowler JH |title=The spread of obesity in a large social network over 32 years |journal=N Engl J Med |volume=357 | |pages=370–9 |year=2007 |pmid=17652652}}</ref> In only very few cases can obesity in humans be attributed to a single gene defect, but many genes have been found that have (usually rare) variants associated with an increased risk of obesity.  
 
===Behavioural and environmental factors===
The ''secular'' increase in overweight and obesity (the increase that has taken place during the 20<sup>th</sup> century and is continuing today) is most obviously due to environmental changes (in the widest sense), the most commonly discussed obesogenic factors being diet and exercise ("The Big Two"). This is not to say that no relevant obesogenic changes in the Human genetic pool happened during this period, and this does not exclude epigenetic modifications of the genome. In a multi-center review of the literature on the possible causes of this secular trend, 10 other factors, including epigenetic changes and modifications in mating behaviours modulating the gene pool, were found to be equally plausible etiologic factors contributing to the epidemic, as Keith ''et al.'' argue.<ref name="pmid16801930">{{cite journal |author=Keith SW, Redden DT, Katzmarzyk PT, ''et al'' |title=Putative contributors to the secular increase in obesity: exploring the roads less traveled |journal=Int J Obes (Lond) |volume=30 |pages=1585–94 |year=2006 |month=November |pmid=16801930 |url=http://www.uab.edu/images/shrp/shrp06/Putative%20contributors%20to%20the%20secular%20increase%20in%20obesity%20-%20exploring%20the%20roads%20less%20traveled.pdf}}</ref>
These factors will be discussed after a critical appraisal of the role of the Big Two.
 
====The Big Two====
 
'''Diet'''
 
'''Sedentarity'''
 
''Also see [[exercise]]''
 
While it is clear that a sedentary lifestyle is involved in the development of a wide range of physical and mental ills, and that overweight and obesity are associated with a more sedentary lifestyle, it is far from obvious that lack of exercise is a major etiological factor in the present obesity epidemic. In a 5.6 years follow-up study of 393 middle-aged healthy subjects (whites), Cambridge epidemiologists demonstrated that carrying excess weight predicted a sedentary lifestyle, but that sedentary time did not predict weight gain.<ref>U Ekelund ''et al.''(2008) Time spent being sedentary and weight gain in healthy adults: reverse or bidirectional causality? ''Am J Clin Nutrition'' 88:612-7</ref>
 
====Other behavioural and environmental factors====
In ''Putative contributors to the secular increase in obesity: exploring the roads less traveled'',<ref name="pmid16801930"/> an analysis published in the [http://www.nature.com/ijo/index.html International Journal of Obesity], reviewers found "evidence (in favor of the following factors was) in many cases (...) as compelling as the evidence for more commonly discussed putative explanations (diet and physical activity)":
 
;Eating habits
Eating quickly and eating until full may be associated with obesity.<ref>{{Cite journal | doi = 10.1136/bmj.a2002 | volume = 337 | issue = oct21_2 | pages = a2002 | last = Maruyama | first = Koutatsu | coauthors = Shinichi Sato, Tetsuya Ohira, Kenji Maeda, Hiroyuki Noda, Yoshimi Kubota, Setsuko Nishimura, Akihiko Kitamura, Masahiko Kiyama, Takeo Okada, Hironori Imano, Masakazu Nakamura, Yoshinori Ishikawa, Michinori Kurokawa, Satoshi Sasaki, Hiroyasu Iso
| title = The joint impact on being overweight of self reported behaviours of eating quickly and eating until full : cross sectional survey | journal = BMJ | accessdate = 2008-10-22 | date = 2008-10-21
| url = http://www.bmj.com/cgi/content/abstract/337/oct21_2/a2002 }}</ref>
 
'''Sleep debt'''
Vgontzas ''et al.'' report primary causes of short sleep duration in obesity as chronic emotional disturbance and various difficulties sleeping.<ref name="pmid18253159">{{cite journal| author=Vgontzas AN, Lin HM, Papaliaga M, Calhoun S, Vela-Bueno A, Chrousos GP et al.| title=Short sleep duration and obesity: the role of emotional stress and sleep disturbances. | journal=Int J Obes (Lond) | year= 2008 | volume= 32 | issue= 5 | pages= 801-9 | pmid=18253159
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=18253159 | doi=10.1038/ijo.2008.4 }} <!--Formatted by http://sumsearch.uthscsa.edu/cite/--></ref>


'''Endocrine disruptors'''
Obesity is generally associated with a state of [[leptin]] resistance, that is analogous to the [[insulin resistance]] seen in [[diabetes mellitus type 2 ]]. Leptin is a [[hormone]] that is secreted into the blood from fat tissues (adipocytes); it acts on the appetite-regulating centres of the [[hypothalamus]] to suppress [[appetite]], and it is secreted at high levels in most obese individuals. However, in these obese individuals, the [[hypothalamus]] does not respond appropriately to leptin.


Endocrine disruptors are man made chemicals interfering with any possible step of hormone signaling. Exposure to low levels of estrogen mimics in the womb can cause "grotesque obesity"<ref name="pmid15959888">{{cite journal |author=Newbold RR, Padilla-Banks E, Snyder RJ, Jefferson WN |title=Developmental exposure to estrogenic compounds and obesity |journal=Birth Defects Res. Part A Clin. Mol. Teratol. |volume=73  |pages=478–80 |year=2005 |month=July |pmid=15959888}}. Also see the [http://www.ourstolenfuture.org/NewScience/obesity/2005/2005-0615newboldetal.html overview] from the [[Our Stolen Future]] online resource:
The role of fetal programming,<ref name="pmid11738796">{{cite journal| author=Breier BH ''et al.''| title=Fetal programming of appetite and obesity|journal=Mol Cell  Endocrinol|year= 2001|volume= 185| pages= 73-9|pmid=11738796| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=11738796}}</ref> <ref name="pmid11479129">{{cite journal| author=Vickers MH ''et al.''| title=Dysregulation of the adipoinsular axis - a mechanism for the  pathogenesis of hyperleptinemia and adipogenic diabetes induced by fetal  programming|journal=J Endocrinol|year= 2001| volume=170| pages= 323-32|pmid=11479129
*'''<u>Excerpts:</u>'''
|url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=11479129}} </ref><ref name="pmid10893326">{{cite journal| author=Vickers MH ''et al.''|title=Fetal  origins of hyperphagia, obesity, and hypertension and postnatal  amplification by hypercaloric nutrition|journal=Am J  Physiol|year=2000|volume=279|pages=E83-7|pmid=10893326
:*This study with mice provides a striking example of how exposure in the womb to an estrogen mimic, diethylstilbestrol, (DES), can lead to grotesque obesity in adulthood. The level of DES required to cause the effect is extremely low... (...) Exposure to synthetic chemicals with estrogenic properties has increased dramatically over the 20th century. One of the most widespread current exposures is to bisphenol A, used to make polycarbonate plastic and other consumer products. Experiments with mice have shown that BPA exposure in the womb causes large increases in post-pubertal weight, and that exposures to very low levels during adulthood can induce insulin resistance. The CDC estimates that 95% of Americans are exposed to bisphenol A at levels within the range of concentrations used in these animal experiments.</ref>. [[Bisphenol(A)]], and perhaps other [[polycyclic aromatic hydrocarbon]]s appears to inhibit the burning of fat by interfering with [[catecholamine]]s.<ref name="pmid16689925">{{cite journal| author=Irigaray P, Ogier V, Jacquenet S, Notet V, Sibille P, Méjean L et al.| title=Benzo[a]pyrene impairs beta-adrenergic stimulation of adipose tissue lipolysis and causes weight gain in mice. A novel molecular mechanism of toxicity for a common food pollutant. | journal=FEBS J | year= 2006 | volume= 273 | issue= 7 | pages= 1362-72 | pmid=16689925
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=10893326}} </ref> perhaps operative in the higher risk of obesity in offspring of older and/or very lean women.
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=16689925 | doi=10.1111/j.1742-4658.2006.05159.x }} <!--Formatted by http://sumsearch.uthscsa.edu/cite/--></ref> Exposure to [[organochlorine]]s decrease [[thyroid hormone]] concentrations, resting [[metabolic rate]], and [[fat oxidation]] in [[skeletal muscles]]<ref name="pmid12608524">{{cite journal |author=Pelletier C, Imbeault P, Tremblay A |title=Energy balance and pollution by organochlorines and polychlorinated biphenyls |journal=Obes Rev |volume=4 |issue=1 |pages=17–24 |year=2003 |month=February |pmid=12608524 |url=http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=1467-7881&date=2003&volume=4&issue=1&spage=17}}</ref>.)


'''Decreased smoking'''
===Environment and lifestyle===
The increase in overweight and obesity that has taken place during the 20<sup>th</sup> century is likely to be due to environmental changes (in the widest sense), including especially lifestyle changes that affect diet and exercise habits. While a sedentary lifestyle is involved in the development of a wide range of physical and mental ills, and obesity is associated with a more sedentary lifestyle, it is not obvious that lack of exercise is a ''major'' factor in the present obesity epidemic. In a 5.6 years follow-up study of 393 middle-aged healthy subjects, Cambridge epidemiologists demonstrated that carrying excess weight predicted a sedentary lifestyle, but that sedentary time did not predict weight gain.<ref>Ekelund U ''et al.''(2008) Time spent being sedentary and weight gain in healthy adults: reverse or bidirectional causality? ''Am J Clin Nutr'' 88:612-7</ref> Failure of sedentary time to predict weight gain might conceivably reflect insufficient sample size to reveal a significant prediction, as might greater errors in estimating sedentary time than measuring weight change.


'''Cultural changes in perceptions of overweight'''<ref name="pmid18617488">{{cite journal |author=Johnson F ''et al.'' |title=Changing perceptions of weight in Great Britain: comparison of two population surveys |journal=BMJ |volume=337 |pages=a494 |year=2008 |pmid=18617488 |doi= |url= |issn=}}</ref>
Many other changes in environment and lifestyle may be involved in the increasing prevalence of obesity. In one multi-center review of the literature, 10 other factors, including epigenetic changes were found to be equally plausible etiologic factors contributing to the epidemic.<ref name="pmid16801930">{{cite journal |author=Keith SW ''et al.''|title=Putative contributors to the secular increase in obesity: exploring the roads less traveled|journal=Int J Obes|volume=30|pages=1585–94|year=2006|pmid=16801930 |url=http://www.uab.edu/images/shrp/shrp06/Putative%20contributors%20to%20the%20secular%20increase%20in%20obesity%20-%20exploring%20the%20roads%20less%20traveled.pdf}}</ref><ref name="pmid19221391">{{cite journal| author=Wansink B, Payne CR| title=The joy of cooking too much: 70 years of calorie increases in classic recipes. | journal=Ann Intern Med | year= 2009 | volume= 150 | issue= 4 | pages= 291-2 | pmid=19221391 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19221391  }} </ref>
Stress and depression (and associated disruptions of sleep) can lead to obesity.<ref name="pmid19808765">{{cite journal|author=Kivimäki M ''et al.''|title=Common mental disorder and obesity: insight from four repeat measures over 19 years: prospective Whitehall II cohort study| journal=BMJ|year=2009|volume=339|pages=b3765|pmid=19808765
|url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=19808765}}</ref> <ref name="pmid18253159">{{cite journal| author=Vgontzas AN ''et al.''| title=Short sleep duration and obesity: the role of emotional stress and sleep disturbances| journal=Int J Obes|year= 2008|volume=32|pages=801-9|pmid=18253159
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=18253159}}</ref><ref name="pmid16801930"/>; changes in eating patterns may contribute<ref>{{Cite journal
| doi = 10.1161/CIR.0b013e31823ac046
| issn = 0009-7322, 1524-4539
| last = Roger
| first = V. L.
| coauthors = A. S. Go, D. M. Lloyd-Jones, E. J. Benjamin, J. D. Berry, W. B. Borden, D. M. Bravata, S. Dai, E. S. Ford, C. S. Fox, H. J. Fullerton, C. Gillespie, S. M. Hailpern, J. A. Heit, V. J. Howard, B. M. Kissela, S. J. Kittner, D. T. Lackland, J. H. Lichtman, L. D. Lisabeth, D. M. Makuc, G. M. Marcus, A. Marelli, D. B. Matchar, C. S. Moy, D. Mozaffarian, M. E. Mussolino, G. Nichol, N. P. Paynter, E. Z. Soliman, P. D. Sorlie, N. Sotoodehnia, T. N. Turan, S. S. Virani, N. D. Wong, D. Woo, M. B. Turner, on behalf of the American Heart Association Statistics Committee and Stroke Statistics Subcommittee
| title = Heart Disease and Stroke Statistics--2012 Update: A Report From the American Heart Association
| journal = Circulation
| accessdate = 2011-12-16
| date = 2011-12-15
| url = http://circ.ahajournals.org/citmgr?gca=circulationaha;CIR.0b013e31823ac046v1
}}</ref><ref name="pmid21738451">{{cite journal| author=Duffey KJ, Popkin BM| title=Energy density, portion size, and eating occasions: contributions to increased energy intake in the United States, 1977-2006. | journal=PLoS Med | year= 2011 | volume= 8 | issue= 6 | pages= e1001050 | pmid=21738451 | doi=10.1371/journal.pmed.1001050 | pmc=PMC3125292 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21738451  }} </ref><ref>{{Cite journal|volume=337|pages= a2002|last = Maruyama|first = K|coauthors = et al.| title = The joint impact on being overweight of self reported behaviours of eating quickly and eating until full : cross sectional survey |journal = BMJ|date = 2008-10-21| url = http://www.bmj.com/cgi/content/abstract/337/oct21_2/a2002}}</ref> and cultural changes in perceptions of overweight<ref name="pmid18617488">{{cite journal |author=Johnson F ''et al.'' |title=Changing perceptions of weight in Great Britain: comparison of two population surveys |journal=BMJ |volume=337|pages=a494 |year=2008 |pmid=18617488}}</ref> Smoking cessation has a well known effect to increase caloric intake.


'''Pharmaceutical iatrogenesis'''
===&nbsp;&nbsp;Evolutionary perspectives of obesity===
To fully understand the causes and prevalence of obesity, evolutionary factors may  need integration into the mix of environmental and genetic proximate causes of obesity. [[Evolutionary medicine]] suggests we get fat because of built-in encouragements to eat heartily when we have plenty to eat and to restrict energy expenditures in preparation for inevitable food shortages. It may also suggest we consider the effect of the types of food we eat compared to those evolution adapted us to eat.  We’ve only recently, on an evolutionary timescale, begun to eat readily absorbable carbohydrates in disproportionate amounts. Our hunter-gatherer ancestors had little access to such food items, with the exception of a bit of honey.  Now we have so-called refined carbohydrates readily available and much consumed. Those include granulated sugar and sucrose dissolved in soft drinks; syrups and candies; milled cereal grain flours and their host pastries, pastas and breads; and many other processed ‘high glycemic’ foods. Those foods stimulate the secretion of insulin as control for glucose homeostasis, and induce other hormonal changes that influence appetite and efficiency of energy utilization. Science writer Gary Taubes summarizes the argument:


Many modern drugs widely used today cause weight gain.
<blockquote>“There is considerable evidence that the obesity epidemic is caused by a hormonal phenomenon, specifically by the consumption of refined carbohydrates, starches and sugars, all of which prompt (sooner or later) excessive insulin secretion. Insulin is the primary regulator of fat storage. When insulin levels are elevated, fat accumulates in our body tissue; when they fall, fat is released and we use it for fuel. By stimulating insulin secretion, carbohydrates make us fat; by driving us to accumulate fat, they increase hunger and decrease the energy we expend in metabolism and physical activity. In short, obesity is caused not by overeating or sedentary behaviour, but by hormonal malfunctioning triggered by the consumption of particular types of carbohydrate-containing foods.”<ref name=taubesns08>Taubes G. (2008) The great diet delusion: It is time for nutrition researchers and health authorities to wake up to the fact that people do not get fat simply because they overeat. ''New Scientist'' 19 January 2008, page 17</ref></blockquote>
 
'''Changes in distribution of ethnicity and age'''
 
Some age and ethnic groups where obesity is more common have grown in number)
 
'''Increasing gravida age'''
 
Giving birth at an older age, which is a worldwide trend, is a risk factor for obesity in the offspring.
 
'''Intrauterine and intergenerational effects'''
 
Trends in obesity incidence may reflect (probably epigenetic) changes that occurred a generation or more before)
 
'''Reproductive fitness'''
 
High BMI leads to reproductive fitness (reproducing at a higher rate)
 
'''Assortative mating and floor effects'''
 
A tendency to search for mates with comparable phenotypes (physical appearance), coupled to a floor effect (a loss of reproductive fitness with increasing leanness), would lead, over time, in a snowball effect to epidemic proportions of overweight.
 
These explanations neither compete with each other, nor with the "Big Two", but demand more depth to the explanations coming out of interventions and researches that are focusing solely on caloric intake and expenditure (diet and exercise).  
 
Nevertheless, any consideration of the role of increased caloric intake and decreased physical energy expenditure must also take into consideration the factors causing them. Some if not many of the above ten 'additional' contributions to the obesity epidemic, plausibly operate proximately to increase caloric intake and/or reduce physical energy expenditure. Sleep debt, for example, produces endocrine/metabolic changes in the body that increase appetite, as Keith ''et al.'' point out.<ref name="pmid16801930" /> One might not find it surprising that people suffering from sleep deprivation reduce their physical energy energy expenditure because of tiredness.  No need to expend much physical energy to keep warm or cool in a thermoneutral environment.  Smoking cessation has a well known effect to increase caloric intake. The role of endocrine disruptors and pharmaceuticals requires further investigation as to the mechanisms of interruption of body weight regulation. Noting greater proportions of ethnic groups that have a propensity to obesity may help explain the rising obesity prevalence but in itself does provide causal mechanisms or exclude the proximate role of the Big Two. Keith ''et al.'' make an important contribution with their study in that their findings indicate that treatment aimed at reversing the "Big Two" will require consideration of the role of a number of factors potentially underpinning them.
 
The role of fetal programming,<ref name="pmid11738796">{{cite journal| author=Breier BH, Vickers MH, Ikenasio BA, Chan KY, Wong WP| title=Fetal programming of appetite and obesity. | journal=Mol Cell Endocrinol | year= 2001 | volume= 185 | issue= 1-2 | pages= 73-9 | pmid=11738796
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=11738796 }} <!--Formatted by http://sumsearch.uthscsa.edu/cite/--></ref><ref name="pmid11479129">{{cite journal| author=Vickers MH, Reddy S, Ikenasio BA, Breier BH| title=Dysregulation of the adipoinsular axis -- a mechanism for the pathogenesis of hyperleptinemia and adipogenic diabetes induced by fetal programming. | journal=J Endocrinol | year= 2001 | volume= 170 | issue= 2 | pages= 323-32 | pmid=11479129
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=11479129 }} <!--Formatted by http://sumsearch.uthscsa.edu/cite/--></ref><ref name="pmid10893326">{{cite journal| author=Vickers MH, Breier BH, Cutfield WS, Hofman PL, Gluckman PD| title=Fetal origins of hyperphagia, obesity, and hypertension and postnatal amplification by hypercaloric nutrition. | journal=Am J Physiol Endocrinol Metab | year= 2000 | volume= 279 | issue= 1 | pages= E83-7 | pmid=10893326
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&email=badgett@uthscdsa.edu&retmode=ref&cmd=prlinks&id=10893326 }} <!--Formatted by http://sumsearch.uthscsa.edu/cite/--></ref>
perhaps operative in the higher risk of obesity in offspring of older and/or very lean women, emerges as an intriguing result of the analysis by Keith et al.<ref name="pmid16801930" />


== Pathophysiology ==
== Pathophysiology ==
'''Appetite: a cause and an effect'''
Obesity is associated with a state of [[leptin]] resistance, analogous to the insulin resistance seen in type 2 [[diabetes]]. Leptin (from the greek'' leptos'', "thin"), being secreted by fat tissues, is high in obese individuals. Nevertheless, the [[hypothalamus]] does not respond proportionately to these concentrations. Leptin is traditionally viewed as a major satiety signal. Indeed, leptin administration suppresses appetite. However, animals who are fed amounts of food comparable to those eaten by animals submitted to the anorexigenic (appetite-suppressing) effects of leptin do not lose weight as fast as their leptin-treated counterparts. <ref name="pmid10712302">{{cite journal |author=Rafael J, Herling AW |title=Leptin effect in ob/ob mice under thermoneutral conditions depends not necessarily on central satiation |journal=Am. J. Physiol. Regul. Integr. Comp. Physiol. |volume=278 |issue=3 |pages=R790–5 |year=2000 |month=March |pmid=10712302 |url=http://ajpregu.physiology.org/cgi/content/full/278/3/R790#Top}}"Reduction of body mass in leptin-treated ob/ob mice was faster than in pair-fed ob/ob controls" (Free full text)</ref> Going a step further, Rafael and colleagues observed that the satiety effect caused by leptin itself could be a ''consequence'' of the "dramatic" increase in fat combustion (lipolysis) elicited by leptin. In other words, leptin would cut appetite because it causes weight loss (by causing fat combustion) rather than, or in addition to, the opposite (for an exploration of the range of possible appetite-independent functions of leptin, see "Perspectives", in the Discussion section of Rafael & al.<ref name="pmid10712302"/>).
A similar change occurred in our understanding of ghrelin, away from hunger signalling, and towards metabolic fine-tuning of energy utilization. [[Ghrelin]] is a hormone secreted by the stomach which is often viewed as the appetite stimulant that counteracts leptin's anorexigenic effect. Again, it appears that this hormone does not act directly as an appetite stimulant, but rather modifies the way in which the body uses fat (versus carbohydrates): it increases fat storage. Concluding their study of mutants unable to secrete ghrelin (and, as a result, less "able" to gain weight when fed a high fat diet), Wortley & al. hypothesise:
<blockquote>''The ability to efficiently build fat reserves in times of nutritional abundance appears to have resulted from evolutionary pressure to protect against subsequent periods of food scarcity. The tendency to efficiently store fat in times of caloric excess appears to have become paradoxically maladaptive in settings of continuous food availability, as indicated by the present epidemic of obesity in Western societies.''<ref name="pmid15148384">{{cite journal |author=Wortley KE, Anderson KD, Garcia K, ''et al'' |title=Genetic deletion of ghrelin does not decrease food intake but influences metabolic fuel preference |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=101 |issue=21 |pages=8227–32 |year=2004 |month=May |pmid=15148384 |doi=10.1073/pnas.0402763101 |url=http://www.pnas.org/cgi/content/full/101/21/8227}}(Free full text)</ref></blockquote>
[[Rimonabant]], a recently developped antagonist of [[endocannabinoid receptor]]s (receptors of endogenous [[cannabis]]-like signalling), is also often thought to induce weight loss (see Treatment, below) by decreasing appetite, as it is called an [[anorectic drug]]. The weight loss, however, extends well beyond the transient decrease in appetite. Studying candy-fed animals, researchers found that rimonabant actually increased the amount of fat available for combustion after a meal, and that this increase in availability was not an indirect, compensatory, consequence of food deprivation, but a direct neuroendocrine effect in its own right.<ref name="pmid18276749">{{cite journal |author=Herling AW, Kilp S, Elvert R, Haschke G, Kramer W |title=Increased energy expenditure contributes more to the body weight-reducing effect of rimonabant than reduced food intake in candy-fed wistar rats |journal=Endocrinology |volume=149 |issue=5 |pages=2557–66 |year=2008 |month=May |pmid=18276749 |doi=10.1210/en.2007-1515 |url=http://endo.endojournals.org/cgi/content/abstract/en.2007-1515v1}} (Free full text)</ref> It is now known that blocking type 1 cannabinoid receptors triggers the birth of new mitochondria (the fat-burning power plants of the cells) in fat cells,<ref name="pmid18477809">{{cite journal |author=Tedesco L, Valerio A, Cervino C, ''et al'' |title=Cannabinoid type 1 receptor blockade promotes mitochondrial biogenesis through eNOS expression in white adipocytes |journal=Diabetes |volume= |issue= |pages= |year=2008 |month=May |pmid=18477809 |doi=10.2337/db07-1623 |url=}}</ref> obviously a beneficial effect for weight loss (also see below, end of section).
'''The response to a meal in obesity: the insulin paradox'''
'''The response to a meal in obesity: the insulin paradox'''


Indeed, all consumers of refined starches, soft drinks, high-fructose corn syrups and other energy-replete products are not born equal. Obese persons, after a meal, appear to burn less efficiently carbohydrates and even more poorly fat.<ref name="pmid11771681">{{cite journal |author=Lopes IM, Forga L, Martínez JA |title=Effects of leptin resistance on acute fuel metabolism after a high carbohydrate load in lean and overweight young men |journal=J Am Coll Nutr |volume=20 |issue=6 |pages=643–8 |year=2001 |month=December |pmid=11771681 |url=http://www.jacn.org/cgi/content/full/20/6/643}} (Free full text)</ref> A contribution of leptin resistance was suggested, since leptin was higher in the obese men that were the least efficient metabolisers of fat. However, the arrow of causality may actually be oriented in the other direction. In persons with a stronger family history of obesity, the earliest obesogenic changes are not related to leptin, but to metabolic efficiency and to insulin status and responsiveness: subjects who are at increased risk of obesity oxidize carbohydrates more quickly, oxidize fat more slowly, and have lower insulin, consistent with a greater than usual insulin sensitivity.<ref name="pmid14970841">{{cite journal |author=Giacco R, Clemente G, Busiello L, ''et al'' |title=Insulin sensitivity is increased and fat oxidation after a high-fat meal is reduced in normal-weight healthy men with strong familial predisposition to overweight |journal=Int. J. Obes. Relat. Metab. Disord. |volume=28 |issue=2 |pages=342–8 |year=2004 |month=February |pmid=14970841 |url=http://www.nature.com/ijo/journal/v28/n2/abs/0802589a.html}} (Free full text)</ref> These findings are in sharp contrast with those implicating obesity with the development, over the long term, of the opposite of insulin sensitivity, i.e. insulin resistance.
All consumers of refined starches, soft drinks, high-fructose corn syrups and other energy-replete products are not born equal. Obese persons, after a meal, appear to burn carbohydrates less efficiently and fat even more poorly.<ref name="pmid11771681">{{cite journal |author=Lopes IM ''et al.''|title=Effects of leptin resistance on acute fuel metabolism after a high carbohydrate load in lean and overweight young men |journal=J Am Coll Nutr |volume=20 |pages=643–8 |year=2001 |pmid=11771681 |url=http://www.jacn.org/cgi/content/full/20/6/643}}</ref> A contribution of leptin resistance was suggested, as circulating concentrations of leptin were higher in the obese men that were the least efficient metabolisers of fat. However, the arrow of causality may be oriented in the other direction. In persons with a family history of obesity, the earliest obesogenic changes are not related to leptin, but to metabolic efficiency and to insulin status and responsiveness: subjects at increased risk of obesity oxidize carbohydrates more quickly and fat more slowly, and have lower insulin, consistent with a greater insulin sensitivity.<ref name="pmid14970841">{{cite journal |author=Giacco R ''et al.'' |title=Insulin sensitivity is increased and fat oxidation after a high-fat meal is reduced in normal-weight healthy men with strong familial predisposition to overweight |journal=Int J Obes Relat Metab Disord|volume=28|pages=342–8 |year=2004 |pmid=14970841 |url=http://www.nature.com/ijo/journal/v28/n2/abs/0802589a.html}}</ref> These findings contrast with those implicating obesity with the development, over the long term, of the opposite of insulin sensitivity, i.e. insulin resistance.


'''Magnesium'''
'''Magnesium'''
 
Obese subjects, like type II diabetics, are magnesium deficient.<ref name="pmid12701060">{{cite journal |author=Takaya J ''et al.'' |title=Intracellular magnesium of platelets in children with diabetes and obesity |journal=Metab Clin Exp|volume=52 |pages=468–71 |year=2003 |pmid=12701060}}</ref> This deficiency is intracellular, and measuring intracellular magnesium requires techniques not yet available in routine clinical settings. Magnesium is required in more than 300 enzymatic reactions, including several that are rate-limiting in carbohydrate utilization. Insulin action depends on magnesium availability in cells and high glucose exposure leads to magnesium depletion and insulin resistance. In obese children, magnesium deficiency precedes insulin resistance<ref name="pmid12701060"/>, but how the heightened responsivity of cells to insulin, that is characteristic of the pre-obese state,<ref name="pmid14970841"/> relates to magnesium deficiency is not known.
Magnesium is involved early in the development of obesity. Obese subjects, like type II diabetics, are magnesium deficient.<ref name="pmid12701060">{{cite journal |author=Takaya J, Higashino H, Kotera F, Kobayashi Y |title=Intracellular magnesium of platelets in children with diabetes and obesity |journal=Metab. Clin. Exp. |volume=52 |issue=4 |pages=468–71 |year=2003 |month=April |pmid=12701060 }} Note that this deficiency is intracellular, and that most of magnesium is present in cells. Measuring intracellular magnesium requires techniques that are not yet available in routine clinical settings.</ref> Magnesium is required in more than 300 enzymatic reactions, including several that are rate-limiting in carbohydrate utilization. Insulin action is closely dependent on magnesium availability in cells and, conversely, high glucose exposure leads to magnesium depletion and insulin resistance. In obese children, magnesium deficiency precedes insulin resistance<ref name="pmid12701060"/>, but how the heightened responsivity of cells to insulin, that is characteristic of the pre-obese state,<ref name="pmid14970841"/> relates to magnesium deficiency is not known.


'''Oxidative stress and reductant stress'''
'''Oxidative stress and reductant stress'''


At the scale of the fat cells, we are facing a paradox similar to the one involving insulin. Obesity may present associated with a range of abnormalities: insulin resistance, chronic inflammation, oxidative stress and a range of ills aggregating in what has been called the metabolic syndrome. It thus appears reasonable to assume that fat cells, in obesity, are in a state of oxidative stress. However, studying obesity in isolation, it became apparent that obesity at the fat cell level required the opposite of oxidative stress, e.g. a balance between oxidants and reductants tilted in favour of the latter.<ref name="pmid16377639">{{cite journal |author=Galinier A, Carrière A, Fernandez Y, ''et al'' |title=Adipose tissue proadipogenic redox changes in obesity |journal=J. Biol. Chem. |volume=281 |issue=18 |pages=12682–7 |year=2006 |month=May |pmid=16377639 |url=http://www.jbc.org/cgi/content/full/281/18/12682}}(Free full text)</ref>
At the scale of the adipocyte, we are facing a paradox similar to the one involving insulin. Obesity may present associated with a range of abnormalities: insulin resistance, chronic inflammation, oxidative stress and a range of ills aggregating in what has been called the metabolic syndrome. It thus appears reasonable to assume that adipocytes, in obesity, are in a state of oxidative stress. However, studying obesity in isolation, it became apparent that obesity at the adipocyte level required the opposite of oxidative stress, e.g. a balance between oxidants and reductants tilted in favour of the latter.<ref name="pmid16377639">{{cite journal |author=Galinier A ''et al.'' |title=Adipose tissue proadipogenic redox changes in obesity |journal=J Biol Chem|volume=281 |pages=12682–7|year=2006 |pmid=16377639 |url=http://www.jbc.org/cgi/content/full/281/18/12682}}</ref>


'''Omega-6 vs. omega-3 unsaturated fatty acids'''
'''Omega-6 vs. omega-3 unsaturated fatty acids'''


The amount of fat to which fat cells are exposed condition their development. The type of fat also is a determinant of fat cell growth (hypertrophy) and multiplication (hyperplasia), a factor that has been largely disregarded until recently. The amount of omega-6 fatty acids in the diet, in absolute terms as well as relative to the amounts of omega-3 fatty acids, have risen sharply since 1945 due to the invention of novel techniques to extract fat from vegetable sources. Omega-6 fatty acids, as a [[prostacyclin]] precursors, enhance [[cyclic AMP]]-dependent signaling pathways in preadipocytes and promote the development of mature adipocytes. Only by modulating the proportion of omega-6 fatty acids in the diet (without increasing total caloric intake), it is possible to cause in animals a 50% increase in body mass.<ref name="pmid12576509">{{cite journal |author=Massiera F, Saint-Marc P, Seydoux J, ''et al'' |title=Arachidonic acid and prostacyclin signaling promote adipose tissue development: a human health concern? |journal=J. Lipid Res. |volume=44 |issue=2 |pages=271–9 |year=2003 |month=February |pmid=12576509 |url=http://www.jlr.org/cgi/content/full/44/2/271}} (Free full text)</ref>
The amount and type of fat to which adipocytes are exposed conditions their development. The amount of omega-6 fatty acids in the diet, in absolute terms as well as relative to the amounts of omega-3 fatty acids, have risen sharply since 1945 due to novel techniques to extract fat from vegetable sources. Omega-6 fatty acids, as a [[prostacyclin]] precursors, enhance [[cyclic AMP]]-dependent signaling pathways in preadipocytes and promote the development of mature adipocytes. Only by modulating the proportion of omega-6 fatty acids in the diet (without increasing total caloric intake), it is possible to cause in animals a 50% increase in body mass.<ref name="pmid12576509">{{cite journal |author=Massiera F ''et al.'' |title=Arachidonic acid and prostacyclin signaling promote adipose tissue development: a human health concern? |journal=J Lipid Res |volume=44 |pages=271–9 |year=2003 |pmid=12576509 |url=http://www.jlr.org/cgi/content/full/44/2/271}}</ref>
 
'''New insights'''


As research advances, it will be possible to evaluate the relative contributions of various factors and identify the most crucial steps leading to obesity. Until recently, it was exceedingly difficult to differenciate between changes that resulted from obesity and those that led to this pathological change: the failure of leptin therapy is a good illustration of the problem (see [[adipocyte]] for details). New methodologies are developped to track and identify the most crucial obesogenic changes.


'''''Starving in a sea of plenty'''''
'''''Starving in a sea of plenty'''''


In March 2008, the [[Public Library of Sciences]] journal published a [[twin study]] that carefully selected, out of a pool of 2,453 young healthy twin pairs, 14 pairs of twins that were discordant for obesity (one twin being obese, and the other not).<ref name="pmid18336063">{{cite journal |author=Pietiläinen KH, Naukkarinen J, Rissanen A, ''et al'' |title=Global transcript profiles of fat in monozygotic twins discordant for BMI: pathways behind acquired obesity |journal=PLoS Med. |volume=5 |issue=3 |pages=e51 |year=2008 |month=March |pmid=18336063 |url=http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050051&ct=1#toclink5}}</ref> This study design allowed to rule out all genetic factors, as well as intrauterine influences and several environmental factors commonly shared amongst siblings of similar ages. The most significant changes that were found in adipocytes were a sharp decrease in the number of mitochondria, the power plants of the cells that are involved in fat burning, and a specific decrease in their ability to oxidize (burn) three amino acids called [[branched-chain amino acids]], that are the first amino acids to be used as fuel when other sources are unavailable. These amino acids, being poorly catabolized, were higher in the circulation; this signalled the release of higher amounts of more insulin, possibly leading to a vicious cycle. Considering metabolic pathways that were, on the contrary, up-regulated, the Finnish researchers found that numerous known and lesser-known inflammatory cascades were overactive. The sharp decline in the number of mitochondria remains the most important finding, which will help to design therapies addressing the fact that, in the disease of affluent civilisations ''par excellence'', fat cells and their energy-producing organelles, the mitochondria, are "starving in a sea of plenty".
In 2008, a [[twin study]] was published which carefully selected, from 2,453 young healthy twin pairs, 14 pairs that were discordant for obesity (one twin being obese, and the other not).<ref name="pmid18336063">{{cite journal |author=Pietiläinen KH ''et al.''|title=Global transcript profiles of fat in monozygotic twins discordant for BMI: pathways behind acquired obesity |journal=PLoS Med|volume=5|pages=e51 |year=2008 |pmid=18336063 |url=http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050051&ct=1#toclink5}}</ref> This study ruled out all genetic factors, as well as intrauterine influences and several environmental factors commonly shared amongst siblings of similar ages. The most significant changes in adipocytes were a sharp decrease in the number of mitochondria, the power plants of the cells that are involved in fat burning, and a specific decrease in their ability to oxidize (burn) three amino acids called [[branched-chain amino acids]], that are the first amino acids to be used as fuel when other sources are unavailable. These amino acids, being poorly catabolized, were higher in the circulation; this signalled the release of higher amounts of more insulin, possibly leading to a vicious cycle. Considering metabolic pathways that were, on the contrary, up-regulated, the researchers found that numerous inflammatory cascades were overactive. The decline in the number of mitochondria remains the most important finding, which will help to design therapies addressing the fact that, in the disease of affluent civilisations ''par excellence'', adipocytes and their energy-producing organelles, the mitochondria, are "starving in a sea of plenty".


'''The gut flora of the obese: the enemy within'''  
'''The gut flora of the obese: the enemy within'''  


The gut flora, which fulfills an essential symbiotic role in animal metabolism, is probably the first victim of a high-fat diet. Before one becomes obese due to dietary excesses, the trillions of micro-organisms which inhabit our intestines have already transformed into a pro-inflammatory, obesogenic organ.<ref name="pmid18326589">{{cite journal |author=Kalliomäki M, Collado MC, Salminen S, Isolauri E |title=Early differences in fecal microbiota composition in children may predict overweight |journal=Am. J. Clin. Nutr. |volume=87 |issue=3 |pages=534–8 |year=2008 |month=March |pmid=18326589 |doi= |url=http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=18326589}}</ref><ref name="pmid18305141">{{cite journal |author=Cani PD, Bibiloni R, Knauf C, ''et al'' |title=Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice |journal=Diabetes |year=2008 |month=March |pmid=18305141 |doi=10.2337/db07-1403}}</ref><ref name="pmid17456850">{{cite journal |author=Cani PD, Amar J, Iglesias MA, ''et al'' |title=Metabolic endotoxemia initiates obesity and insulin resistance |journal=Diabetes |volume=56 |issue=7 |pages=1761–72 |year=2007 |month=July |pmid=17456850 |doi=10.2337/db06-1491 |url=http://diabetes.diabetesjournals.org/cgi/content/full/56/7/1761}} (Free full text)</ref>
The gut flora, which fulfills an essential symbiotic role in animal metabolism, is probably the first victim of a high-fat diet. Before one becomes obese due to dietary excesses, the trillions of micro-organisms which inhabit our intestines have already transformed into a pro-inflammatory, obesogenic organ.<ref name="pmid18326589">{{cite journal |author=Kalliomäki M ''et al.'' |title=Early differences in fecal microbiota composition in children may predict overweight |journal=Am J Clin Nutr|volume=87|pages=534–8 |year=2008|pmid=18326589}}</ref><ref name="pmid18305141">{{cite journal |author=Cani PD ''et al.'' |title=Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice |journal=Diabetes |year=2008 |pmid=18305141}}</ref><ref name="pmid17456850">{{cite journal|author=Cani PD ''et al.'' |title=Metabolic endotoxemia initiates obesity and insulin resistance|journal=Diabetes|volume=56 |pages=1761–72|year=2007|pmid=17456850 |url=http://diabetes.diabetesjournals.org/cgi/content/full/56/7/1761}}</ref>


==Treatment==
==Treatment==
''See also [[Bariatric surgery]], [[Drug treatments for obesity]] and [[Exercise and body weight]]''
''See also [[Bariatric surgery]], [[Drug treatments for obesity]] and [[Exercise and body weight]]''


The mainstay of treatment for obesity is an energy-limited [[dieting|diet]] and increased [[Physical exercise|exercise]]. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass (excluding study drop-outs). While not all dieters will be satisfied with this outcome, studies have shown that a loss of as little as 5% of body mass can create large health benefits. A more intractable [[Sociotherapy|therapeutic]] problem appears to be weight loss maintenance. Of dieters who manage to lose 10% or more of their [[body mass]] in studies, 80-95% will regain that weight within two to five years, supporting the finding that the body has various mechanisms that maintain weight at a certain set point.
The mainstay of treatment for obesity is an energy-limited [[dieting|diet]] and increased [[Physical exercise|exercise]]. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass (excluding study drop-outs). While not all dieters will be satisfied with this outcome, a loss of as little as 5% of body mass can create large health benefits. A more intractable [[Sociotherapy|therapeutic]] problem appears to be weight loss maintenance. Of dieters who manage to lose 10% or more of their [[body mass]] in studies, 80-95% will regain that weight within two to five years, supporting the finding that the body has various mechanisms that maintain weight at a certain set point.


In a [[clinical practice guideline]] by the [[American College of Physicians]], the following five recommendations are made:<ref name=Snow2005>{{cite journal | author=Snow V, Barry P, Fitterman N, Qaseem A, Weiss K | title=Pharmacologic and surgical management of obesity in primary care: a clinical practice guideline from the American College of Physicians | journal=Ann Intern Med | year=2005 | pages=525-31 | volume=142 | issue=7 | id=PMID 15809464}} [http://www.annals.org/cgi/content/full/142/7/525 Fulltext].</ref>
A [[clinical practice guideline]] issued by the [[American College of Physicians]] in 2005 made five recommendations:<ref name=Snow2005>{{cite journal | author=Snow V ''et al.''| title=Pharmacologic and surgical management of obesity in primary care: a clinical practice guideline from the American College of Physicians| journal=Ann Intern Med | year=2005| pages=525-31| volume=142|id=PMID 15809464}} [http://www.annals.org/cgi/content/full/142/7/525].</ref>
# People with a BMI of over 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss.
# People with a BMI above 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss.
# If these goals are not achieved, pharmacotherapy can be offered. The patient needs to be informed of the possibility of [[Adverse effect (medicine)|side-effects]] and the unavailability of long-term safety and efficacy data.
# If these goals are not achieved, pharmacotherapy can be offered. The patient needs to be informed of the possibility of [[Adverse effect (medicine)|side-effects]] and the unavailability of long-term safety and efficacy data.
# Drug therapy may consist of [[sibutramine]], [[orlistat]], [[phentermine]], [[diethylpropion]], [[fluoxetine]], and [[bupropion]]. For more severe cases of obesity, stronger drugs such as [[amphetamine]] and [[methamphetamine]] may be used on a selective basis.  Evidence is not sufficient to recommend [[sertraline]], [[topiramate]], or [[zonisamide]].
# Drug therapy may consist of [[sibutramine]], [[orlistat]], [[phentermine]], [[diethylpropion]], [[fluoxetine]], and [[bupropion]]. For more severe cases of obesity, stronger drugs such as [[amphetamine]] and [[methamphetamine]] may be used on a selective basis.  Evidence is not sufficient to recommend [[sertraline]], [[topiramate]], or [[zonisamide]].
Line 148: Line 80:
# Those requiring bariatric surgery should be referred to high-volume referral centers, as the evidence suggests that surgeons who frequently perform these procedures have fewer complications.
# Those requiring bariatric surgery should be referred to high-volume referral centers, as the evidence suggests that surgeons who frequently perform these procedures have fewer complications.


A [[clinical practice guideline]] by the [[US Preventive Services Task Force]] (USPSTF) concluded that the evidence is insufficient to recommend for or against routine behavioral counseling to promote a healthy diet in unselected patients in primary care settings, but that intensive behavioral dietary counseling is recommended in those with [[hyperlipidemia]] and other known risk factors for cardiovascular and diet-related chronic disease. Intensive counseling can be delivered by primary care clinicians or by referral to other specialists, such as nutritionists or dietitians.<ref>{{cite web |url=http://www.ngc.gov/summary/summary.aspx?ss=15&doc_id=3494 |title=Behavioral counseling in primary care to promote a healthy diet: recommendations and rationale. |accessdate=2007-05-22 |format= |work=}}</ref><ref name="pmid12554027">{{cite journal |author=Pignone MP, Ammerman A, Fernandez L, ''et al'' |title=Counseling to promote a healthy diet in adults: a summary of the evidence for the U.S. Preventive Services Task Force |journal=American journal of preventive medicine |volume=24 |issue=1 |pages=75-92 |year=2003 |pmid=12554027 |doi=}}</ref>
A [[clinical practice guideline]] by the [[U.S. Preventive Services Task Force]] (USPSTF) concluded that the evidence is insufficient to recommend for or against routine behavioral counseling to promote a healthy diet in unselected patients in primary care settings, but that intensive behavioral dietary counseling is recommended in those with [[hyperlipidemia]] and other known risk factors for cardiovascular and diet-related chronic disease. Intensive counseling can be delivered by primary care clinicians or by referral to other specialists, such as nutritionists or dietitians.<ref>{{cite web |url=http://www.ngc.gov/summary/summary.aspx?ss=15&doc_id=3494 |title=Behavioral counseling in primary care to promote a healthy diet: recommendations and rationale. |accessdate=2007-05-22}}</ref><ref name="pmid12554027">{{cite journal |author=Pignone MP ''et al.'' |title=Counseling to promote a healthy diet in adults: a summary of the evidence for the U.S. Preventive Services Task Force|journal=Am J Prev Med|volume=24|pages=75-92|year=2003|pmid=12554027}}</ref>


===Counseling===
===Counseling===
A [[meta-analysis]] of [[randomized controlled trial]]s concluded that "compared with usual care, dietary counseling interventions produce modest weight losses that diminish over time."<ref name="pmid17606960">{{cite journal |author=Dansinger ML ''et al.'' |title=Meta-analysis: the effect of dietary counseling for weight loss |journal=Ann Intern Med |volume=147 |pages=41-50 |year=2007 |pmid=17606960 |doi=|url=http://www.annals.org/cgi/content/full/147/1/41}}</ref>
A [[meta-analysis]] of [[randomized controlled trial]]s concluded that "compared with usual care, dietary counseling interventions produce modest weight losses that diminish over time."<ref name="pmid17606960">{{cite journal |author=Dansinger ML ''et al.'' |title=Meta-analysis: the effect of dietary counseling for weight loss|journal=Ann Intern Med |volume=147|pages=41-50 |year=2007 |pmid=17606960}}</ref>
 
The role of genetic counseling is unclear<ref name="pmid15216550">{{cite journal|author=Marteau T ''et al.'' |title=Psychological impact of genetic testing for familial hypercholesterolemia within a previously aware population: a randomized controlled trial |journal=Am J Med Genet A|volume=128  |pages=285–93 |year=2004 |pmid=15216550 }}</ref>; but based on a study done of hypercholesterolemia, it is possible that genetic counseling might lead to patients preferring medication over diet therapy.<ref name="pmid17879121">{{cite journal |author=Rief W ''et al.''|title=Is information on genetic determinants of obesity helpful or harmful for obese people?-A randomized clinical trial |journal=J Gen Intern Med|volume=22|pages=1553–9|year=2007|pmid=17879121}}</ref>


The role of genetic counseling is unclear<ref name="pmid15216550">{{cite journal |author=Marteau T ''et al.'' |title=Psychological impact of genetic testing for familial hypercholesterolemia within a previously aware population: a randomized controlled trial |journal=Am J Med Genet A |volume=128  |pages=285–93 |year=2004 |pmid=15216550 |doi=10.1002/ajmg.a.30102}}</ref>; however, based on a study done of hypercholesterolemia, it is possible that genetic counseling might lead to patients preferring medication over diet therapy.<ref name="pmid17879121">{{cite journal |author=Rief W ''et al.'' |title=Is information on genetic determinants of obesity helpful or harmful for obese people?--A randomized clinical trial |journal=J Gen Intern Med |volume=22  |pages=1553–9 |year=2007 |pmid=17879121 |doi=10.1007/s11606-007-0353-7}}</ref>
====Delivery method for counseling====
* Personal contact may better sustain weight loss<ref name="pmid18334689">{{cite journal| author=Svetkey LP, Stevens VJ, Brantley PJ, Appel LJ, Hollis JF, Loria CM et al.| title=Comparison of strategies for sustaining weight loss: the weight loss maintenance randomized controlled trial. | journal=JAMA | year= 2008 | volume= 299 | issue= 10 | pages= 1139-48 | pmid=18334689 | doi=10.1001/jama.299.10.1139 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18334689  }} [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18667668 Review in: Evid Based Med. 2008 Aug;13(4):109]  [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18624372 Review in: ACP J Club. 2008 Jul;149(1):4] </ref>
* The [[Internet]] may increase [[patient participation]] in their health care.<ref name="pmid12684363">{{cite journal| author=Tate DF, Jackvony EH, Wing RR| title=Effects of Internet behavioral counseling on weight loss in adults at risk for type 2 diabetes: a randomized trial. | journal=JAMA | year= 2003 | volume= 289 | issue= 14 | pages= 1833-6 | pmid=12684363 | doi=10.1001/jama.289.14.1833 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12684363  }} </ref><ref name="pmid18201641">{{cite journal|author=Hunter CM ''et al.''|title=Weight management using the internet a randomized controlled trial|journal=Am J Prev Med|volume=34|pages=119–26|year=2008 |pmid=18201641}}</ref>
* High-frequency [[telephone]] contact may help.<ref name="pmid19221377">{{cite journal| author=Digenio AG, Mancuso JP, Gerber RA, Dvorak RV| title=Comparison of methods for delivering a lifestyle modification program for obese patients: a randomized trial. | journal=Ann Intern Med | year= 2009 | volume= 150 | issue= 4 | pages= 255-62 | pmid=19221377 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19221377  }} </ref>


The [[Internet]] offer a method to increase [[patient participation]] in their health care. A randomized controlled trial showed some benefit in a weight loss program that used the Internet.<ref name="pmid18201641">{{cite journal |author=Hunter CM ''et al'' |title=Weight management using the internet a randomized controlled trial |journal=Am J Prev Med |volume=34 |pages=119–26 |year=2008 |pmid=18201641 |doi=10.1016/j.amepre.2007.09.026}}</ref>
===Diets===
{{main|Diet (weight loss)}}


====Portion control plate====
====Portion control====
A randomized controlled trial found that patients using portion control plates and log books had more weight loss and less use of hypoglycemic drugs.<ref name="pmid17592101">{{cite journal |author=Pedersen SD ''et al.''|title=Portion control plate for weight loss in obese patients with type 2 diabetes mellitus: a controlled clinical trial |journal=Arch Intern Med|volume=167 |pages=1277–83 |year=2007 |pmid=17592101 |doi=10.1001/archinte.167.12.1277 |issn=}} [http://www.acpjc.org/Content/147/3/issue/ACPJC-2007-147-3-068.htm ACP Journal Club review]</ref>
A randomized controlled trial found that patients using portion control plates and log books had more weight loss and less use of hypoglycemic drugs.<ref name="pmid17592101">{{cite journal |author=Pedersen SD ''et al.''|title=Portion control plate for weight loss in obese patients with type 2 diabetes mellitus: a controlled clinical trial |journal=Arch Intern Med|volume=167|pages=1277–83 |year=2007|pmid=17592101}}[http://www.acpjc.org/Content/147/3/issue/ACPJC-2007-147-3-068.htm ACP Journal Club review]</ref>


====Drink more water====
====Drink more water====
Encouraging more water drinking may help.<ref name="pmid19336356">{{cite journal |author=Muckelbauer R ''et al.'' |title=Promotion and provision of drinking water in schools for overweight prevention: randomized, controlled cluster trial |journal=Pediatrics |volume=123|pages=e661–7 |year=2009|pmid=19336356 |doi=10.1542/peds.2008-2186 |url=http://pediatrics.aappublications.org/cgi/pmidlookup?view=long&pmid=19336356 |issn=}}</ref>
Encouraging more water drinking may help.<ref name="pmid19336356">{{cite journal|author=Muckelbauer R ''et al.''|title=Promotion and provision of drinking water in schools for overweight prevention: randomized, controlled cluster trial|journal=Pediatrics|volume=123|pages=e661–7|year=2009|pmid=19336356|url=http://pediatrics.aappublications.org/cgi/pmidlookup?view=long&pmid=19336356}}</ref>


====Financial incentives====
====Financial incentives====
Financial incentives may help.<ref name="pmid19066383">{{cite journal |author=Volpp KG ''et al.''|title=Financial incentive-based approaches for weight loss: a randomized trial |journal=JAMA |volume=300 |pages=2631–7 |year=2008 |month=December |pmid=19066383 |doi=10.1001/jama.2008.804 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=19066383 |issn=}}</ref> A website names [http://www.stickk.com/ stickK] uses financial contracts to motivate people to loose weight and change other behaviors.
Financial incentives may help.<ref name="pmid19066383">{{cite journal |author=Volpp KG ''et al.''|title=Financial incentive-based approaches for weight loss: a randomized trial|journal=JAMA |volume=300 |pages=2631–7|year=2008 |pmid=19066383|url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=19066383}}</ref>
 
===Diets===
{|align="right" class="wikitable"
|+ Descriptions of common diets
! Diet!! Description
|-
| [[American Heart Association]] diet<ref name="pmid11056107">{{cite journal |author=Krauss RM, Eckel RH, Howard B, ''et al'' |title=AHA Dietary Guidelines: revision 2000: A statement for healthcare professionals from the Nutrition Committee of the American Heart Association |journal=Circulation |volume=102 |issue=18 |pages=2284–99 |year=2000 |month=October |pmid=11056107 |doi= |url=http://circ.ahajournals.org/cgi/pmidlookup?view=long&pmid=11056107 |issn=}}</ref> || low fat
|-
| [[Atkins diet|Dr Atkins' diet]] || Carbohydrate-restricted<br> initially < 20 g of carbohydrate daily, subsequently  50 g/day
|-
| [[LEARN diet]] || low fat
|-
| [[Mediterranean diet]]<ref name="isbn0-7432-6642-0">{{cite book |author= |authorlink= |editor= |others= |title=Eat, Drink, and Be Healthy : The Harvard Medical School Guide to Healthy Eating |edition= |language= |publisher=Free Press |location=New York |year=2005 |origyear= |pages= |quote= |isbn=0-7432-6642-0 |oclc= |doi= |url= |accessdate=|id={{LCC| RA784 .W635}}}}</ref> || moderate-fat (<35% of calories) emphasizing monounsaturated fats
|-
| [[Ornish diet]] || vegetarian, low fat
|-
| [[Rosemary Conley]] || low-fat and social support
|-
| [[Slim-Fast]] plan || low glycemic index
|-
| [[SouthBeach diet]] plan || Carbohydrate-restricted; meal replacement
|-
| [[Weight Watchers]] || balanced diet with social support
|-
| [[Zone diet]] || low-carbohydrate diet<br> carbohydrates, proteins, and fats in 40:30:30 ratio
|}
 
The [[United States]] [[Department of Health and Human Services]] and [[Department of Agriculture]] jointly recommend:<ref>{{cite web |url=http://www.health.gov/dietaryguidelines/dga2005/recommendations.htm |title=Key Recommendations for the General Population, Dietary Guidelines for Americans 2005 |author= |authorlink= |coauthors= |date=2005 |format= |work= |publisher=United States Department of Agriculture |pages= |language= |archiveurl= |archivedate= |quote= |accessdate=2008-07-01}}</ref>
* "Keep total fat intake between 20 to 35 percent of calories."
** "Consume less than 10 percent of calories from saturated fatty acids"
** "Less  than 300 mg/day of cholesterol"
** "Keep trans fatty acid consumption as low as  possible"
* "The Average Macronutrient Distribution Range (AMDR) for carbohydrates is 45  to 65 percent of total calories."
** "The recommended [[dietary fiber]] intake is 14 grams per 1,000 calories consumed."
 
MyPyramid.gov offer online dietary support at http://www.mypyramidtracker.gov/.
 
Various alternative dietary approaches have been proposed, some of which have been compared by [[randomized controlled trial]]s:
* A comparison of varying fat and protein levels found no difference on weight loss.<ref name="pmid19246357">Sacks et al. Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates. N Engl J Med 2009. PMID 19246357</ref> The lowest-carbohydrate group had a slightly better improvement in the HDL.
* A comparison of [[Atkins diet|Dr Atkins' diet]], [[Slim-Fast]] plan, [[Weight Watchers]] "pure points programme", and [[Rosemary Conley]]'s found no significant differences.<ref name="pmid16720619">{{cite journal |author=Truby H ''et al.'' |title=Randomised controlled trial of four commercial weight loss programmes in the UK: initial findings from the BBC "diet trials" |journal=BMJ |volume=332 |pages=1309-14 |year=2006 |pmid=16720619 |doi=10.1136/bmj.38833.411204.80}}</ref>
* A comparison of Atkins, [[Zone diet]], [[Ornish diet]], and [[LEARN diet]] in ''premenopausal women'' found the greatest benefit from the [[Atkins diet]].<ref name="pmid17341711">{{cite journal |author=Gardner CD ''et al'' |title=Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial |journal=JAMA |volume=297  |pages=969-77 |year=2007 |pmid=17341711 |doi=10.1001/jama.297.9.969}}</ref>
* A comparison of [[Atkins diet]], [[Zone diet]], [[Weight Watchers]], and [[Ornish diet]] noted:<ref name="pmid15632335">{{cite journal |author=Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ |title=Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial |journal=JAMA |volume=293 |issue=1 |pages=43-53 |year=2005 |pmid=15632335 |doi=10.1001/jama.293.1.43}}</ref>
: "all 4 diets resulted in modest statistically significant weight loss at 1 year, with no statistically significant differences between diets"
: "The higher discontinuation rates for the Atkins and Ornish diet groups suggest many individuals found these diets to be too extreme"
* A comparison of three diets: 1) low-fat, restricted-calorie; 2) Mediterranean, restricted-calorie; or 3) low-carbohydrate, non-restricted-calorie found:<ref name="pmid18635428">{{cite journal |author=Shai I, Schwarzfuchs D, Henkin Y, ''et al'' |title=Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet |journal=N. Engl. J. Med. |volume=359 |issue=3 |pages=229–41 |year=2008 |month=July |pmid=18635428 |doi=10.1056/NEJMoa0708681 |url=http://content.nejm.org/cgi/pmidlookup?view=short&pmid=18635428&promo=ONFLNS19 |issn=}}</ref>
** ''Least weight'' loss occurred in the low-fat, restricted-calorie group
** More favorable effects on lipids with the low-carbohydrate diet
** More favorable effects on glycemic control with the Mediterranean diet
 
====Carbohydrate-restricted (low carbohydrate) versus fat-restricted (low fat) diets====
Many studies have focused on diets that reduce calories via a low-carbohydrate ([[Atkins diet]], [[South Beach diet]],  [[Zone diet]]) diet (< 20-30 grams/day of carbohydrate) versus a low-fat diet ([[LEARN diet]], [[Ornish diet]]). The [[Nurses' Health Study]], an observational [[cohort study]], found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less [[coronary heart disease]].<ref name="pmid17093250">{{cite journal |author=Halton TL ''et al.'' |title=Low-carbohydrate-diet score and the risk of coronary heart disease in women |journal=N Engl J Med |volume=355 |pages=1991-2002 |year=2006 |pmid=17093250 |doi=10.1056/NEJMoa055317}}</ref>
 
* A comparison of three diets: 1) low-fat, restricted-calorie; 2) Mediterranean, restricted-calorie; or 3) low-carbohydrate, non-restricted-calorie found:<ref name="pmid18635428">{{cite journal |author=Shai I, Schwarzfuchs D, Henkin Y, ''et al'' |title=Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet |journal=N. Engl. J. Med. |volume=359 |issue=3 |pages=229–41 |year=2008 |month=July |pmid=18635428 |doi=10.1056/NEJMoa0708681 |url=http://content.nejm.org/cgi/pmidlookup?view=short&pmid=18635428&promo=ONFLNS19 |issn=}}</ref>
** ''Least weight'' loss occurred in the low-fat, restricted-calorie group
** More favorable effects on lipids with the low-carbohydrate diet
** More favorable effects on glycemic control with the Mediterranean diet
 
A [[meta-analysis]] that included older [[randomized controlled trial]]s<ref name="pmid12761364">{{cite journal |author=Samaha FF, Iqbal N, Seshadri P, ''et al'' |title=A low-carbohydrate as compared with a low-fat diet in severe obesity |journal=N. Engl. J. Med. |volume=348 |issue=21 |pages=2074–81 |year=2003 |pmid=12761364 |doi=10.1056/NEJMoa022637}}</ref><ref name="pmid12761365">{{cite journal |author=Foster GD ''et al.'' |title=A randomized trial of a low-carbohydrate diet for obesity |journal=N Engl J Med |volume=348  |pages=2082–90 |year=2003 |pmid=12761365 |doi=10.1056/NEJMoa022207}}</ref><ref name="pmid15632335"/> (but not the two more recent studies above) found:<ref name="pmid16476868">{{cite journal |author=Nordmann AJ ''et al.'' |title=Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials |journal=Arch. Intern. Med. |volume=166  |pages=285-93 |year=2006 |pmid=16476868 |doi=10.1001/archinte.166.3.285}}</ref>
:"low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."


An older [[meta-analysis]] of [[randomized controlled trial]]s by the [[Cochrane Collaboration]] in 2002 concluded<ref name="pmid12076496">{{cite journal |author=Pirozzo S ''et al.'' |title=Advice on low-fat diets for obesity |journal=Cochrane database of systematic reviews (Online) |volume=  |pages=CD003640 |year=2002 |pmid=12076496 |doi=}}</ref> that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people.
===Food labeling===
The Nutrition Labeling and Education Act (NLEA) of 1990 went into effect in 1994 to require labeling on on packaged foods.


The [[Women's Health Initiative]] Randomized Controlled Dietary Modification Trial<ref name="pmid16391215">{{cite journal |author=Howard BV ''et al.'' |title=Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial |journal=JAMA |volume=295 |pages=39-49 |year=2006 |pmid=16391215 |doi=10.1001/jama.295.1.39}}</ref> found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily:
New York City required labeling by restaurants with 15 or more outlets to post caloric content starting July, 2008.<ref name="pmid20375399">{{cite journal| author=Nestle M| title=Health care reform in action--calorie labeling goes national. | journal=N Engl J Med | year= 2010 | volume= 362 | issue= 25 | pages= 2343-5 | pmid=20375399 | doi=10.1056/NEJMp1003814 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20375399  }} </ref> The New York law may increase awareness of calories.<ref name="pmid19808705">{{cite journal| author=Elbel B, Kersh R, Brescoll VL, Dixon LB| title=Calorie labeling and food choices: a first look at the effects on low-income people in New York City. | journal=Health Aff (Millwood) | year= 2009 | volume= 28 | issue= 6 | pages= w1110-21 | pmid=19808705 | doi=10.1377/hlthaff.28.6.w1110 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19808705  }} </ref><ref name="pmid20966367">{{cite journal| author=Dumanovsky T, Huang CY, Bassett MT, Silver LD| title=Consumer awareness of fast-food calorie information in New York City after implementation of a menu labeling regulation. | journal=Am J Public Health | year= 2010 | volume= 100 | issue= 12 | pages= 2520-5 | pmid=20966367 | doi=10.2105/AJPH.2010.191908 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20966367  }} </ref>
* no reduction in cardiovascular disease<ref name="pmid16467234">{{cite journal |author=Howard BV ''et al.'' |title=Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial |journal=JAMA |volume=295  |pages=655-66 |year=2006 |pmid=16467234 |doi=10.1001/jama.295.6.655}}</ref>
* an insignificant reduction in invasive breast cancer<ref name="pmid16467232">{{cite journal |author=Prentice RL, Caan B, Chlebowski RT, ''et al'' |title=Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial |journal=JAMA |volume=295 |issue=6 |pages=629-42 |year=2006 |pmid=16467232 |doi=10.1001/jama.295.6.629}}</ref>
* no reductions in colorectal cancer<ref name="pmid16467233">{{cite journal |author=Beresford SA ''et al.'' |title=Low-fat dietary pattern and risk of colorectal cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial |journal=JAMA |volume=295  |pages=643-54 |year=2006 |pmid=16467233 |doi=10.1001/jama.295.6.643}}</ref>


Other [[randomized controlled trial]]s have found that:
Public Law 111-147, the Patient Protection and Affordable Care Act, mandates that restaurants with 20 or more outlets nationwide post caloric information “in a clear and conspicuous manner.”<ref name="pmid20375399">{{cite journal| author=Nestle M| title=Health care reform in action--calorie labeling goes national. | journal=N Engl J Med | year= 2010 | volume= 362 | issue= 25 | pages= 2343-5 | pmid=20375399 | doi=10.1056/NEJMp1003814 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20375399  }} </ref>
* A comparison of Atkins, [[Zone diet]], [[Ornish diet]], and [[LEARN diet]] in ''premenopausal women'' found the greatest benefit from the [[Atkins diet]].<ref name="pmid17341711">{{cite journal |author=Gardner CD ''et al'' |title=Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial |journal=JAMA |volume=297  |pages=969-77 |year=2007 |pmid=17341711 |doi=10.1001/jama.297.9.969}}</ref>


* The choice of diet for a specific person may be influenced by measuring the invididual's insulin secretion:
===Medications===
:In [[young adults]] "Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion."<ref name="pmid17507345">{{cite journal |author=Ebbeling CB ''et al.''|title=Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial |journal=JAMA |volume=297  |pages=2092-102 |year=2007 |pmid=17507345 |doi=10.1001/jama.297.19.2092}}</ref> This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.<ref name="pmid15148064">{{cite journal |author=Stern ''et al.'' |title=The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial |journal=Ann Intern Med |volume=140|pages=778–85 |year=2004 |pmid=15148064 |doi=}}</ref><ref name="pmid7848401">{{cite journal |author=Garg A ''et al.'' |title=Effects of varying carbohydrate content of diet in patients with non-insulin-dependent diabetes mellitus |journal=JAMA |volume=271 |pages=1421–8 |year=1994 |pmid=7848401 |doi=}}</ref>
{{main|Drug treatments for obesity}}
 
====Low glycemic index and low glycemic load diets====
{{main|glycemic index}}
A [[meta-analysis]] by the [[Cochrane Collaboration]] concluded that low [[glycemic index]] or low glycemic load diets led to more weight loss and better lipid profiles. ''However'', the [[Cochrane Collaboration]] grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.<ref name="pmid17636786">{{cite journal |author=Thomas DE, Elliott E, Baur L |title=Low glycaemic index or low glycaemic load diets for overweight and obesity |journal=Cochrane database of systematic reviews (Online) |volume=  |pages=CD005105 |year=2007 |pmid=17636786 |doi=10.1002/14651858.CD005105.pub2}}</ref>
 
A [[randomized controlled trial]] that compared four diets that varied in carbohydrate amount and glycemic index found complicated results<ref name="pmid16864756">{{cite journal |author=McMillan-Price J ''et al.'' |title=Comparison of 4 diets of varying glycemic load on weight loss and cardiovascular risk reduction in overweight and obese young adults: a randomized controlled trial |journal=Arch Intern Med |volume=166  |pages=1466-75 |year=2006 |pmid=16864756 |doi=10.1001/archinte.166.14.1466}}</ref>:
* Diet 1 and 2 were high carbohydrate (55% of total energy intake)
** Diet 1 was high-glycemic index
** Diet 2 was low-glycemic index
* Diet 3 and 4 were high protein (25% of total energy intake)
** Diet 3 was high-glycemic index
** Diet 4 was low-glycemic index
 
Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index  diet was the most favorable.
 
====High versus standard protein====
There was no difference from amount of [[protein]] according to a [[randomized controlled trial]].<ref name="pmid18752682">{{cite journal |author=Treyzon L, Chen S, Hong K, ''et al'' |title=A controlled trial of protein enrichment of meal replacements for weight reduction with retention of lean body mass |journal=Nutr J |volume=7 |issue=1 |pages=23 |year=2008 |month=August |pmid=18752682 |doi=10.1186/1475-2891-7-23 |url=http://www.nutritionj.com/content/7/1/23 |issn=}}</ref>
 
===Exercise===
''See [[Exercise and body weight]]
 
===Reduction of ambient temperature===
When ambient temperatures decrease below certain levels, the body must make homeostatic and adaptive adjustments to maintain optimal body temperature. Those adjustments entail increased body heat production that add to total energy expenditure. Thus, it has been hypothesized that lowering ambient temperatures in homes and workplaces will contribute to mitigation of obesogenesis.<ref name=hansen2010>Hansen JC, Gilman AP, Odland JO. (2010) [http://dx.doi.org/10.1016/j.mehy.2010.02.033 Is thermogenesis a significant causal factor in preventing the ‘‘globesity” epidemic?]. ''Med Hypotheses''. In press as of 16 May 2010.</ref>
 
===Drugs===
''See [[Drug treatments for obesity]]''
 
Many drugs reduce appetite by activating [[serotonin]] 5-HT<sub>2C</sub> receptor. This may occur via:
* Nonselective activation of multiple [[biogenic monoamine]]s by reuptake inhibition. [[Sibutramine]] and [[tesofensine]]<ref name="pmid18950853">{{cite journal |author=Astrup A ''et al.''|title=Effect of tesofensine on bodyweight loss, body composition, and quality of life in obese patients: a randomised, double-blind, placebo-controlled trial |journal=Lancet |volume=372 |pages=1906–13 |year=2008 |month=November |pmid=18950853 |doi=10.1016/S0140-6736(08)61525-1 |url=http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(08)61525-1 |issn=}}</ref> have this mechanism.
* Non-selective agonism of [[serotonin]] 5-HT<sub>2B</sub> receptorr as well as the 5-HT<sub>2C</sub> receptors by [[fenfluramine]] and [[dexfenfluramine]] may damage [[heart valve]]s via agonism of 5-HT<sub>2B</sub> receptors on [[heart valve]]s.
* Selective agonism of [[serotonin]] 5-HT<sub>2C</sub> receptors by drugs such as [[lorcaserin]] decreases appetite via the [[proopiomelanocortin]] system.<ref name="10.1056/NEJMoa0909809">{{Cite journal | doi = 10.1056/NEJMoa0909809 | volume = 363  | pages = 245-56 | last = Smith | first = SR | coauthors = ''et al.''| title = Multicenter, placebo-controlled trial of Lorcaserin for weight management | journal = N Engl J Med | accessdate = 2010-07-15 | date = 2010-07-15 | url = http://content.nejm.org/cgi/content/abstract/363/3/245 }}</ref>
 
[[Orlistat]] is an inhibitor of gastrointestinal [[lipase]].
 
For patients with [[diabetes mellitus type 2]], [[metformin]] can assist in weight loss—rather than [[sulfonylurea]] derivatives and [[insulin]], which often lead to further weight gain.  The [[thiazolidinedione]]s ([[rosiglitazone]] or [[pioglitazone]]) can cause slight weight gain, but decrease the "pathologic" form of abdominal fat, and so may help obese diabetics.
 
====Effectiveness====
A [[systematic review]] found that the average weight loss after at least one year was:<ref name="pmid18006966">{{cite journal |author=Rucker D ''et al.''|title=Long term pharmacotherapy for obesity and overweight: updated meta-analysis |journal=BMJ |volume=  |pages= |year=2007 |pmid=18006966 |doi=10.1136/bmj.39385.413113.25}}</ref>
* [[Orlistat]]:  2.9 kg, but with gastrointestinal side effects.
* [[Sibutramine]]: 4.2 kg, but with raised blood pressure and pulse.
* [[Rimonabant]]: 4.7-kg, but associated with increased  psychiatric disorders. About a third of patients discontinued treatment.<ref name="pmid18022033">{{cite journal |author=Christensen R ''et al.'' |title=Efficacy and safety of the weight-loss drug rimonabant: a meta-analysis of randomised trials |journal=Lancet |volume=370 |pages=1706–13 |year=2007 |pmid=18022033 |doi=10.1016/S0140-6736(07)61721-8 |issn=}}</ref><ref name="pmid18006966"/>
 
Subsequent trials show:
*[[Tesofensine]] may be effective<ref name="pmid18950853">{{cite journal |author=Astrup A ''et al.'' |title=Effect of tesofensine on bodyweight loss, body composition, and quality of life in obese patients: a randomised, double-blind, placebo-controlled trial |journal=Lancet |volume=372 |issue=9653 |pages=1906–13 |year=2008 |month=November |pmid=18950853 |doi=10.1016/S0140-6736(08)61525-1 |url=http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(08)61525-1 |issn=}}</ref>
* [[Lorcaserin]] may be effective<ref name="10.1056/NEJMoa0909809">{{Cite journal | doi = 10.1056/NEJMoa0909809  | volume = 363 | pages = 245-256 | last = Smith | first =  SR| coauthors = ''et al.''| title = Multicenter, placebo-controlled trial of Lorcaserin for weight management | journal = N Engl J Med |  accessdate = 2010-07-15 | date = 2010-07-15 | url = http://content.nejm.org/cgi/content/abstract/363/3/245  }}</ref>


===Bariatric surgery===
===Bariatric surgery===
{{main|Bariatric surgery}}
''[[Bariatric surgery]]'' (or "weight loss surgery") is the use of surgical interventions in the treatment of obesity. As every surgical intervention may lead to complications, it is regarded as a last resort when dietary modification and pharmacological treatment have proven to be unsuccessful.
''[[Bariatric surgery]]'' (or "weight loss surgery") is the use of surgical interventions in the treatment of obesity. As every surgical intervention may lead to complications, it is regarded as a last resort when dietary modification and pharmacological treatment have proven to be unsuccessful.
 
In the U.S.A.,[[Medicare]] will only only pay for procedures performed at approved facilities.<ref name="urlBariatric Surgery">{{cite web |url=http://www.cms.hhs.gov/MedicareApprovedFacilitie/BSF/|title=Bariatric Surgery |publisher=Centers for Medicare & Medicaid Services|accessdate=2008-06-26}}</ref>
In the [[United States]], [[Medicare]] will only only pay for procedures performed at approved facilities.<ref name="urlBariatric Surgery">{{cite web |url=http://www.cms.hhs.gov/MedicareApprovedFacilitie/BSF/ |title=Bariatric Surgery |publisher=Centers for Medicare & Medicaid Services|format= |work= |accessdate=2008-06-26}}</ref>
 
====Types of surgery====
Weight loss surgery relies on various principles.  Band surgery is reversible, while bowel shortening operations are not. Some procedures can be performed [[laparoscopic surgery|laparoscopically]].
 
* '''Predominantly restrictive procedures'''. The most common approaches are reducing the volume of the stomach, producing an earlier sense of satiation (e.g. by [[adjustable gastric band]]ing and [[Vertical banded gastroplasty surgery|vertical banded gastroplasty]]).
* '''Predominantly restrictive procedures'''. The most common approaches are reducing the volume of the stomach, producing an earlier sense of satiation (e.g. by [[adjustable gastric band]]ing and [[Vertical banded gastroplasty surgery|vertical banded gastroplasty]]).
* '''Predominantly malabsorptive procedures''' Others procedures also reduce the length of bowel that food will be in contact with, directly reducing absorption ([[gastric bypass surgery]]).
* '''Predominantly malabsorptive procedures''' Others procedures also reduce the length of bowel that food will be in contact with, directly reducing absorption ([[gastric bypass surgery]]).


In general, the malabsorptive procedures lead to more weight loss than the restrictive procedures. A [[meta-analysis]] by the [[American College of Physicians]] reports the following weight loss at 36 months:<ref name="pmid15809466">{{cite journal |author=Maggard MA ''et al.'' |title=Meta-analysis: surgical treatment of obesity |journal=Ann. Intern. Med. |volume=142 |pages=547–59 |year=2005 |pmid=15809466 |doi=}}</ref>
Band surgery is reversible, while gastric bypass surgery is not. In general, gastric bypass surgery leads to more weight loss than band surgery. A [[meta-analysis]] by the [[American College of Physicians]] reports the following weight loss at 36 months:<ref name="pmid15809466">{{cite journal |author=Maggard MA ''et al.''|title=Meta-analysis: surgical treatment of obesity|journal=Ann Intern Med|volume=142|pages=547–59|year=2005|pmid=15809466}}</ref>
* Biliopancreatic diversion - 53 kg
* Biliopancreatic diversion - 53 kg
* Roux-en-Y gastric bypass (RYGB) - 41 kg
* Roux-en-Y gastric bypass - 41 kg (Open - 42 kg; Laparoscopic - 38 kg)
** Open - 42 kg
** Laparoscopic - 38 kg
* Adjustable gastric banding - 35 kg
* Adjustable gastric banding - 35 kg
* Vertical banded gastroplasty - 32 kg
* Vertical banded gastroplasty - 32 kg


This meta-analysis does not include a more recent [[randomized controlled trial]].<ref>Nguyen, Ninh T et al. [http://journals.lww.com/annalsofsurgery/Abstract/2009/10000/A_Prospective_Randomized_Trial_of_Laparoscopic.14.aspx A prospective randomized trial of laparoscopic gastric bypass versus laparoscopic adjustable gastric banding for the treatment of morbid obesity: Outcomes, quality of life, and costs]. Annals of Surgery. 2009;250(4):631-641. {{doi|10.1097/SLA.0b013e3181b92480}}</ref>
This analysis does not include a more recent [[randomized controlled trial]].<ref>Nguyen NT ''et al.'' (2009)[http://journals.lww.com/annalsofsurgery/Abstract/2009/10000/A_Prospective_Randomized_Trial_of_Laparoscopic.14.aspx A prospective randomized trial of laparoscopic gastric bypass versus laparoscopic adjustable gastric banding for the treatment of morbid obesity: Outcomes, quality of life, and costs] ''Ann Surg'' 250:631-41}}</ref>


=====Mortality=====
Two studies report decreases in mortality from bariatric surgery.<ref name="pmid17715408">{{cite journal|author=Sjöström L ''et al.''|title=Effects of bariatric surgery on mortality in Swedish obese subjects |journal=N Engl J Med|volume=357|pages=741-52|year=2007|pmid=17715408 |doi=10.1056/NEJMoa066254}}</ref><ref name="pmid17715409">{{cite journal |author=Adams TD ''et al.'' |title=Long-term mortality after gastric bypass surgery |journal=N Engl J Med |volume=357|pages=753-61 |year=2007 |pmid=17715409 }}</ref> In the Swedish [[randomized controlled trial]], patients with a BMI of 34 or more for men and 38 or more for women underwent various types of bariatric surgery and were followed for a mean of 11 years. Surgery patients had 5% mortality while control patients had 6.3% mortality. <ref name="pmid17715408"/> In a Utah retrospective [[cohort study]] that followed patients for a mean of 7 years after various types of gastric bypass, surgery patients had 0.4% mortality while control patients had 0.6% mortality.<ref name="pmid17715409"/>
Two studies report decrease in mortality from bariatric surgery.<ref name="pmid17715408">{{cite journal |author=Sjöström L ''et al.'' |title=Effects of bariatric surgery on mortality in Swedish obese subjects |journal=N Engl J Med |volume=357 |pages=741-52 |year=2007 |pmid=17715408 |doi=10.1056/NEJMoa066254}}</ref><ref name="pmid17715409">{{cite journal |author=Adams TD ''et al.'' |title=Long-term mortality after gastric bypass surgery |journal=N Engl J Med |volume=357 |pages=753-61 |year=2007 |pmid=17715409 |doi=10.1056/NEJMoa066603}}</ref> In the Swedish [[randomized controlled trial]], patients with a [[body mass index]] of 34 or more for men and 38 or more for women underwent various types of bariatric surgery and were followed for a mean of 11 years. Surgery patients had 5.0% mortality while control patients had 6.3% mortality. This means 75 patients must be treated to avoid one death after 11 years ([[number needed to treat]] is 77).<ref name="pmid17715408"/> In a Utah retrospective [[cohort study]] that followed patients for a mean of 7 years after various types of gastric bypass, surgery patients had 0.4% mortality while control patients had 0.6% mortality.<ref name="pmid17715409"/>


=====Remission of diabetes=====
Bariatric surgery remits [[diabetes mellitus type 2]] in more than 1 of every two people after 2 years if they are similar to the patients in the [[randomized controlled trial]] by Dixon ''et al.''.<ref name="pmid18212316">{{cite journal |author=Dixon JB ''et al.'' |title=Adjustable gastric banding and conventional therapy for type 2 diabetes: a randomized controlled trial |journal=JAMA |volume=299 |pages=316–23 |year=2008 |pmid=18212316 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=18212316}}</ref>  In this trial, 73% of the patients remitted their diabetes versus 13% of the patients in the control group.
Bariatric surgery remits [[diabetes mellitus type 2]] in more than 1 of every two people after 2 years if they are similar to the patients in the [[randomized controlled trial]] / [[meta-analysis]] by Dixon ''et al.'' ([[Number needed to treat]] is 1.7).<ref name="pmid18212316">{{cite journal |author=Dixon JB, O'Brien PE, Playfair J, ''et al'' |title=Adjustable gastric banding and conventional therapy for type 2 diabetes: a randomized controlled trial |journal=JAMA |volume=299 |issue=3 |pages=316–23 |year=2008 |month=January |pmid=18212316 |doi=10.1001/jama.299.3.316 |url=http://jama.ama-assn.org/cgi/pmidlookup?view=long&pmid=18212316 |issn=}}</ref>  In this trial 73% of the patients who remitted their diabetes versus 13% of the patients in the control group.


==Prevention==
==Prevention==
Display of calorie information on the menus or menu boards of restaurants has been proposed by the city of New York.<ref name="nyt">Rivera R. (2007) “New York City Reintroduces Calorie Rule,” The New York Times, October 25, 2007, http://www.nytimes.com/2007/10/25/nyregion/25calories.html (accessed October 26, 2007).</ref>
Display of calorie information on the menus or menu boards of restaurants has been proposed by the city of New York.<ref name="nyt">Rivera R (2007) “New York City Reintroduces Calorie Rule,” The New York Times, October 25, 2007, http://www.nytimes.com/2007/10/25/nyregion/25calories.html (accessed October 26, 2007)</ref>


Eating breakfast may reduce weight gain by adolescents<ref name="pmid18310183">{{cite journal |author=Timlin MT, Pereira MA, Story M, Neumark-Sztainer D |title=Breakfast eating and weight change in a 5-year prospective analysis of adolescents: Project EAT (Eating Among Teens) |journal=Pediatrics |volume=121 |issue=3 |pages=e638-45 |year=2008 |pmid=18310183 |doi=10.1542/peds.2007-1035 |url=http://pediatrics.aappublications.org/cgi/pmidlookup?view=long&pmid=18310183}}</ref>
Eating breakfast may reduce weight gain by adolescents<ref name="pmid18310183">{{cite journal |author=Timlin MT ''et al.'' |title=Breakfast eating and weight change in a 5-year prospective analysis of adolescents: Project EAT (Eating Among Teens) |journal=Pediatrics |volume=121 |pages=e638-45 |year=2008 |pmid=18310183 |url=http://pediatrics.aappublications.org/cgi/pmidlookup?view=long&pmid=18310183}}</ref>


==References==
==References==
{{Reflist|2}}
{{Reflist|2}}[[Category:Suggestion Bot Tag]]

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Obesity is the medical condition associated with excessive stores of body fat, to the extent that it causes serious health risks. Physical problems include high blood pressure, heart disease, some cancers and Diabetes mellitus type 2; emotional problems include low self esteem, and depression. More than a billion people are classed as obese worldwide, and by 2025, 300 million people are expected to suffer from obesity-related diabetes.

There are many ways of measuring body fat, but the most common measures the relationship between weight and height by the body mass index (BMI). A BMI of 30 or more puts you in the category of obese. This method is simple, but imprecise; people with well-developed muscle may have a high BMI yet a low proportion of body fat.

Prevalence and epidemiology

Obesity is increasing in Europe.[1] In the U.S.A., obesity is increased through 2004[2] but has been stable since[3]. Among immigrants, the incidence of obesity increases with the duration of living in the U.S.A..[4]

Causes/etiology

See Genetics of obesity

The proximate cause of obesity is a mix of environmental and genetic factors.[5][6] In only very few cases can obesity in humans be attributed to a single gene defect, but many genes have been found that have (usually rare) variants associated with an increased risk of obesity.

Obesity is generally associated with a state of leptin resistance, that is analogous to the insulin resistance seen in diabetes mellitus type 2 . Leptin is a hormone that is secreted into the blood from fat tissues (adipocytes); it acts on the appetite-regulating centres of the hypothalamus to suppress appetite, and it is secreted at high levels in most obese individuals. However, in these obese individuals, the hypothalamus does not respond appropriately to leptin.

The role of fetal programming,[7] [8][9] perhaps operative in the higher risk of obesity in offspring of older and/or very lean women.

Environment and lifestyle

The increase in overweight and obesity that has taken place during the 20th century is likely to be due to environmental changes (in the widest sense), including especially lifestyle changes that affect diet and exercise habits. While a sedentary lifestyle is involved in the development of a wide range of physical and mental ills, and obesity is associated with a more sedentary lifestyle, it is not obvious that lack of exercise is a major factor in the present obesity epidemic. In a 5.6 years follow-up study of 393 middle-aged healthy subjects, Cambridge epidemiologists demonstrated that carrying excess weight predicted a sedentary lifestyle, but that sedentary time did not predict weight gain.[10] Failure of sedentary time to predict weight gain might conceivably reflect insufficient sample size to reveal a significant prediction, as might greater errors in estimating sedentary time than measuring weight change.

Many other changes in environment and lifestyle may be involved in the increasing prevalence of obesity. In one multi-center review of the literature, 10 other factors, including epigenetic changes were found to be equally plausible etiologic factors contributing to the epidemic.[11][12] Stress and depression (and associated disruptions of sleep) can lead to obesity.[13] [14][11]; changes in eating patterns may contribute[15][16][17] and cultural changes in perceptions of overweight[18] Smoking cessation has a well known effect to increase caloric intake.

  Evolutionary perspectives of obesity

To fully understand the causes and prevalence of obesity, evolutionary factors may need integration into the mix of environmental and genetic proximate causes of obesity. Evolutionary medicine suggests we get fat because of built-in encouragements to eat heartily when we have plenty to eat and to restrict energy expenditures in preparation for inevitable food shortages. It may also suggest we consider the effect of the types of food we eat compared to those evolution adapted us to eat. We’ve only recently, on an evolutionary timescale, begun to eat readily absorbable carbohydrates in disproportionate amounts. Our hunter-gatherer ancestors had little access to such food items, with the exception of a bit of honey. Now we have so-called refined carbohydrates readily available and much consumed. Those include granulated sugar and sucrose dissolved in soft drinks; syrups and candies; milled cereal grain flours and their host pastries, pastas and breads; and many other processed ‘high glycemic’ foods. Those foods stimulate the secretion of insulin as control for glucose homeostasis, and induce other hormonal changes that influence appetite and efficiency of energy utilization. Science writer Gary Taubes summarizes the argument:

“There is considerable evidence that the obesity epidemic is caused by a hormonal phenomenon, specifically by the consumption of refined carbohydrates, starches and sugars, all of which prompt (sooner or later) excessive insulin secretion. Insulin is the primary regulator of fat storage. When insulin levels are elevated, fat accumulates in our body tissue; when they fall, fat is released and we use it for fuel. By stimulating insulin secretion, carbohydrates make us fat; by driving us to accumulate fat, they increase hunger and decrease the energy we expend in metabolism and physical activity. In short, obesity is caused not by overeating or sedentary behaviour, but by hormonal malfunctioning triggered by the consumption of particular types of carbohydrate-containing foods.”[19]

Pathophysiology

The response to a meal in obesity: the insulin paradox

All consumers of refined starches, soft drinks, high-fructose corn syrups and other energy-replete products are not born equal. Obese persons, after a meal, appear to burn carbohydrates less efficiently and fat even more poorly.[20] A contribution of leptin resistance was suggested, as circulating concentrations of leptin were higher in the obese men that were the least efficient metabolisers of fat. However, the arrow of causality may be oriented in the other direction. In persons with a family history of obesity, the earliest obesogenic changes are not related to leptin, but to metabolic efficiency and to insulin status and responsiveness: subjects at increased risk of obesity oxidize carbohydrates more quickly and fat more slowly, and have lower insulin, consistent with a greater insulin sensitivity.[21] These findings contrast with those implicating obesity with the development, over the long term, of the opposite of insulin sensitivity, i.e. insulin resistance.

Magnesium Obese subjects, like type II diabetics, are magnesium deficient.[22] This deficiency is intracellular, and measuring intracellular magnesium requires techniques not yet available in routine clinical settings. Magnesium is required in more than 300 enzymatic reactions, including several that are rate-limiting in carbohydrate utilization. Insulin action depends on magnesium availability in cells and high glucose exposure leads to magnesium depletion and insulin resistance. In obese children, magnesium deficiency precedes insulin resistance[22], but how the heightened responsivity of cells to insulin, that is characteristic of the pre-obese state,[21] relates to magnesium deficiency is not known.

Oxidative stress and reductant stress

At the scale of the adipocyte, we are facing a paradox similar to the one involving insulin. Obesity may present associated with a range of abnormalities: insulin resistance, chronic inflammation, oxidative stress and a range of ills aggregating in what has been called the metabolic syndrome. It thus appears reasonable to assume that adipocytes, in obesity, are in a state of oxidative stress. However, studying obesity in isolation, it became apparent that obesity at the adipocyte level required the opposite of oxidative stress, e.g. a balance between oxidants and reductants tilted in favour of the latter.[23]

Omega-6 vs. omega-3 unsaturated fatty acids

The amount and type of fat to which adipocytes are exposed conditions their development. The amount of omega-6 fatty acids in the diet, in absolute terms as well as relative to the amounts of omega-3 fatty acids, have risen sharply since 1945 due to novel techniques to extract fat from vegetable sources. Omega-6 fatty acids, as a prostacyclin precursors, enhance cyclic AMP-dependent signaling pathways in preadipocytes and promote the development of mature adipocytes. Only by modulating the proportion of omega-6 fatty acids in the diet (without increasing total caloric intake), it is possible to cause in animals a 50% increase in body mass.[24]


Starving in a sea of plenty

In 2008, a twin study was published which carefully selected, from 2,453 young healthy twin pairs, 14 pairs that were discordant for obesity (one twin being obese, and the other not).[25] This study ruled out all genetic factors, as well as intrauterine influences and several environmental factors commonly shared amongst siblings of similar ages. The most significant changes in adipocytes were a sharp decrease in the number of mitochondria, the power plants of the cells that are involved in fat burning, and a specific decrease in their ability to oxidize (burn) three amino acids called branched-chain amino acids, that are the first amino acids to be used as fuel when other sources are unavailable. These amino acids, being poorly catabolized, were higher in the circulation; this signalled the release of higher amounts of more insulin, possibly leading to a vicious cycle. Considering metabolic pathways that were, on the contrary, up-regulated, the researchers found that numerous inflammatory cascades were overactive. The decline in the number of mitochondria remains the most important finding, which will help to design therapies addressing the fact that, in the disease of affluent civilisations par excellence, adipocytes and their energy-producing organelles, the mitochondria, are "starving in a sea of plenty".

The gut flora of the obese: the enemy within

The gut flora, which fulfills an essential symbiotic role in animal metabolism, is probably the first victim of a high-fat diet. Before one becomes obese due to dietary excesses, the trillions of micro-organisms which inhabit our intestines have already transformed into a pro-inflammatory, obesogenic organ.[26][27][28]

Treatment

See also Bariatric surgery, Drug treatments for obesity and Exercise and body weight

The mainstay of treatment for obesity is an energy-limited diet and increased exercise. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass (excluding study drop-outs). While not all dieters will be satisfied with this outcome, a loss of as little as 5% of body mass can create large health benefits. A more intractable therapeutic problem appears to be weight loss maintenance. Of dieters who manage to lose 10% or more of their body mass in studies, 80-95% will regain that weight within two to five years, supporting the finding that the body has various mechanisms that maintain weight at a certain set point.

A clinical practice guideline issued by the American College of Physicians in 2005 made five recommendations:[29]

  1. People with a BMI above 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss.
  2. If these goals are not achieved, pharmacotherapy can be offered. The patient needs to be informed of the possibility of side-effects and the unavailability of long-term safety and efficacy data.
  3. Drug therapy may consist of sibutramine, orlistat, phentermine, diethylpropion, fluoxetine, and bupropion. For more severe cases of obesity, stronger drugs such as amphetamine and methamphetamine may be used on a selective basis. Evidence is not sufficient to recommend sertraline, topiramate, or zonisamide.
  4. In patients with BMI > 40 who fail to achieve their weight loss goals (with or without medication) and who develop obesity-related complications, referral for bariatric surgery may be indicated. The patient needs to be aware of the potential complications.
  5. Those requiring bariatric surgery should be referred to high-volume referral centers, as the evidence suggests that surgeons who frequently perform these procedures have fewer complications.

A clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF) concluded that the evidence is insufficient to recommend for or against routine behavioral counseling to promote a healthy diet in unselected patients in primary care settings, but that intensive behavioral dietary counseling is recommended in those with hyperlipidemia and other known risk factors for cardiovascular and diet-related chronic disease. Intensive counseling can be delivered by primary care clinicians or by referral to other specialists, such as nutritionists or dietitians.[30][31]

Counseling

A meta-analysis of randomized controlled trials concluded that "compared with usual care, dietary counseling interventions produce modest weight losses that diminish over time."[32]

The role of genetic counseling is unclear[33]; but based on a study done of hypercholesterolemia, it is possible that genetic counseling might lead to patients preferring medication over diet therapy.[34]

Delivery method for counseling

Diets

For more information, see: Diet (weight loss).


Portion control

A randomized controlled trial found that patients using portion control plates and log books had more weight loss and less use of hypoglycemic drugs.[39]

Drink more water

Encouraging more water drinking may help.[40]

Financial incentives

Financial incentives may help.[41]

Food labeling

The Nutrition Labeling and Education Act (NLEA) of 1990 went into effect in 1994 to require labeling on on packaged foods.

New York City required labeling by restaurants with 15 or more outlets to post caloric content starting July, 2008.[42] The New York law may increase awareness of calories.[43][44]

Public Law 111-147, the Patient Protection and Affordable Care Act, mandates that restaurants with 20 or more outlets nationwide post caloric information “in a clear and conspicuous manner.”[42]

Medications

For more information, see: Drug treatments for obesity.


Bariatric surgery

For more information, see: Bariatric surgery.

Bariatric surgery (or "weight loss surgery") is the use of surgical interventions in the treatment of obesity. As every surgical intervention may lead to complications, it is regarded as a last resort when dietary modification and pharmacological treatment have proven to be unsuccessful. In the U.S.A.,Medicare will only only pay for procedures performed at approved facilities.[45]

  • Predominantly restrictive procedures. The most common approaches are reducing the volume of the stomach, producing an earlier sense of satiation (e.g. by adjustable gastric banding and vertical banded gastroplasty).
  • Predominantly malabsorptive procedures Others procedures also reduce the length of bowel that food will be in contact with, directly reducing absorption (gastric bypass surgery).

Band surgery is reversible, while gastric bypass surgery is not. In general, gastric bypass surgery leads to more weight loss than band surgery. A meta-analysis by the American College of Physicians reports the following weight loss at 36 months:[46]

  • Biliopancreatic diversion - 53 kg
  • Roux-en-Y gastric bypass - 41 kg (Open - 42 kg; Laparoscopic - 38 kg)
  • Adjustable gastric banding - 35 kg
  • Vertical banded gastroplasty - 32 kg

This analysis does not include a more recent randomized controlled trial.[47]

Two studies report decreases in mortality from bariatric surgery.[48][49] In the Swedish randomized controlled trial, patients with a BMI of 34 or more for men and 38 or more for women underwent various types of bariatric surgery and were followed for a mean of 11 years. Surgery patients had 5% mortality while control patients had 6.3% mortality. [48] In a Utah retrospective cohort study that followed patients for a mean of 7 years after various types of gastric bypass, surgery patients had 0.4% mortality while control patients had 0.6% mortality.[49]

Bariatric surgery remits diabetes mellitus type 2 in more than 1 of every two people after 2 years if they are similar to the patients in the randomized controlled trial by Dixon et al..[50] In this trial, 73% of the patients remitted their diabetes versus 13% of the patients in the control group.

Prevention

Display of calorie information on the menus or menu boards of restaurants has been proposed by the city of New York.[51]

Eating breakfast may reduce weight gain by adolescents[52]

References

  1. ↑ Kotseva K et al. (2009). "Cardiovascular prevention guidelines in daily practice: a comparison of EUROASPIRE I, II, and III surveys in eight European countries". Lancet 373: 929–40. PMID 19286092.
  2. ↑ Ogden CL et al. (2006). "Prevalence of overweight and obesity in the United States, 1999-2004". JAMA 295: 1549–55. PMID 16595758.
  3. ↑ Ogden CL et al. (2008). "High body mass index for age among US children and adolescents, 2003-2006". JAMA 299: 2401–5. PMID 18505949.
  4. ↑ Goel MS et al. (2004). "Obesity among US immigrant subgroups by duration of residence". JAMA 292: 2860–7. PMID 15598917.
  5. ↑ Stunkard AJ et al. (1990). "The body-mass index of twins who have been reared apart". N Eng J Med 322: 1483–7. PMID 2336075.
  6. ↑ Christakis NA, Fowler JH (2007). "The spread of obesity in a large social network over 32 years". N Engl J Med 357: 370–9. PMID 17652652.
  7. ↑ Breier BH et al. (2001). "Fetal programming of appetite and obesity". Mol Cell Endocrinol 185: 73-9. PMID 11738796.
  8. ↑ Vickers MH et al. (2001). "Dysregulation of the adipoinsular axis - a mechanism for the pathogenesis of hyperleptinemia and adipogenic diabetes induced by fetal programming". J Endocrinol 170: 323-32. PMID 11479129.
  9. ↑ Vickers MH et al. (2000). "Fetal origins of hyperphagia, obesity, and hypertension and postnatal amplification by hypercaloric nutrition". Am J Physiol 279: E83-7. PMID 10893326.
  10. ↑ Ekelund U et al.(2008) Time spent being sedentary and weight gain in healthy adults: reverse or bidirectional causality? Am J Clin Nutr 88:612-7
  11. ↑ 11.0 11.1 Keith SW et al. (2006). "Putative contributors to the secular increase in obesity: exploring the roads less traveled". Int J Obes 30: 1585–94. PMID 16801930.
  12. ↑ Wansink B, Payne CR (2009). "The joy of cooking too much: 70 years of calorie increases in classic recipes.". Ann Intern Med 150 (4): 291-2. PMID 19221391. [e]
  13. ↑ Kivimäki M et al. (2009). "Common mental disorder and obesity: insight from four repeat measures over 19 years: prospective Whitehall II cohort study". BMJ 339: b3765. PMID 19808765.
  14. ↑ Vgontzas AN et al. (2008). "Short sleep duration and obesity: the role of emotional stress and sleep disturbances". Int J Obes 32: 801-9. PMID 18253159.
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  30. ↑ Behavioral counseling in primary care to promote a healthy diet: recommendations and rationale.. Retrieved on 2007-05-22.
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  36. ↑ Tate DF, Jackvony EH, Wing RR (2003). "Effects of Internet behavioral counseling on weight loss in adults at risk for type 2 diabetes: a randomized trial.". JAMA 289 (14): 1833-6. DOI:10.1001/jama.289.14.1833. PMID 12684363. Research Blogging.
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  42. ↑ 42.0 42.1 Nestle M (2010). "Health care reform in action--calorie labeling goes national.". N Engl J Med 362 (25): 2343-5. DOI:10.1056/NEJMp1003814. PMID 20375399. Research Blogging.
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  45. ↑ Bariatric Surgery. Centers for Medicare & Medicaid Services. Retrieved on 2008-06-26.
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  50. ↑ Dixon JB et al. (2008). "Adjustable gastric banding and conventional therapy for type 2 diabetes: a randomized controlled trial". JAMA 299: 316–23. PMID 18212316.
  51. ↑ Rivera R (2007) “New York City Reintroduces Calorie Rule,” The New York Times, October 25, 2007, http://www.nytimes.com/2007/10/25/nyregion/25calories.html (accessed October 26, 2007)
  52. ↑ Timlin MT et al. (2008). "Breakfast eating and weight change in a 5-year prospective analysis of adolescents: Project EAT (Eating Among Teens)". Pediatrics 121: e638-45. PMID 18310183.
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