Obesity
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2008-07-16T14:46:08Z
Jmh649
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/* Exercise */
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{{DiseaseDisorder infobox |
Name = Obesity |
Image = Obesity-waist circumference.PNG |
Caption = Silhouettes representing standard, overweight, and obese. |
DiseasesDB = 9099 |
ICD10 = {{ICD10|E|66| |e|65}} |
ICD9 = {{ICD9|278}} |
MedlinePlus = 003101 |
eMedicineSubj = med |
eMedicineTopic =1653 |
MeshName = Obesity |
MeshNumber = C23.888.144.699.500 |
}}
'''Obesity''' is a [[disease]] in which excess body fat has accumulated to such an extent that health may be negatively affected.<ref name=WHO2000/> It is commonly defined as a [[body mass index]] (weight divided by height squared) of 30 kg/m<sup>2</sup> or higher.<ref name=WHO2000/> This distinguishes it from being [[overweight]] as defined by a BMI of between 25-29.9.<ref name=WHO2000/> Many studies show an association between excessive body weight and various [[diseases]], particularly [[cardiovascular diseases]], [[diabetes mellitus type 2]], [[sleep apnea]], certain types of [[cancer]], and [[osteoarthritis]].<ref name=NHLBI>{{cite book |author=National Heart, Lung, and Blood Institute |title=Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults |publisher=International Medical Publishing, Inc |location= |year= |pages= |isbn=1-58808-002-1 |oclc= |url=http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.pdf}}</ref><ref name=HaslamJames>{{cite journal |author=Haslam DW, James WP |title=Obesity |journal=Lancet |volume=366 |issue=9492 |pages=1197–209 |year=2005 |pmid=16198769 |doi=10.1016/S0140-6736(05)67483-1}}</ref> As a result, obesity has been found to reduce [[life expectancy]].<ref name=HaslamJames/> Although obesity is an individual clinical condition, most authorities view it as a serious and growing [[public health]] problem that needs to be addressed by encouraging healthy dietary choices and physical exercise on a population-wide scale.<ref name=NICECG043/>
==Classification==
Obesity in absolute terms is an increase of body [[adipose tissue|fatty tissue]] mass. In a practical setting it is difficult to measure this directly, and obesity is typically measured by BMI ([[body mass index]]) and in terms of its distribution through waist circumference or waist-hip circumference ratio measurements.<ref>{{cite journal |journal= Nutr J |date=2007 |volume=6 |pages=32 |title= Measurement and definitions of obesity in childhood and adolescence: a field guide for the uninitiated |author= Sweeting HN |doi=10.1186/1475-2891-6-32 |pmid=17963490 |url=http://www.nutritionj.com/content/6/1/32}}</ref> In addition, the presence of obesity needs to be evaluated in the context of other [[risk factor]]s and [[comorbidities]] (other medical conditions that could influence risk of complications).<ref name=NHLBI/>
===BMI===
[[Body mass index]] or BMI is a simple and widely used method for estimating body fat mass.<ref>{{cite journal | author=Mei Z, Grummer-Strawn LM, Pietrobelli A, Goulding A, Goran MI, Dietz WH | title=Validity of body mass index compared with other body-composition screening indexes for the assessment of body fatness in children and adolescents | journal=Am J Clin Nutr | year=2002 | volume=75 | pages=978–85 | pmid=12036802 | url=http://www.ajcn.org/cgi/content/full/75/6/978}}</ref> BMI was developed in the 19th century by the [[Belgium|Belgian]] statistician and [[anthropometry|anthropometrist]] [[Adolphe Quetelet]].<ref>{{cite book | author=Quetelet LAJ | year=1871 | title=Antropométrie ou Mesure des Différences Facultés de l'Homme | location=Brussels | publisher=Musquardt}}</ref> BMI is an accurate reflection of body fat percentage in the majority of the adult population, but is less accurate in situations that affect body composition such as in [[body building|body builders]] and [[pregnancy]].<ref name=NHLBI/>
BMI is calculated by dividing the subject's weight by the square of his/her height, typically expressed either in [[Metric system|metric]] or [[US customary units|US "Customary"]] units:
:Metric: <math>BMI = kg/m^2</math>
Where <math>kg</math> is the subject's weight in kilograms and <math>m</math> is the subject's height in metres.
:US/Customary and [[Imperial System|imperial]]: <math>BMI=lb*703/in^2</math>
Where <math>lb</math> is the subject's weight in [[pound (mass)|pounds]] and <math>in</math> is the subject's height in [[inches]].
The most commonly used definitions, established by the [[World Health Organization|WHO]] in 1997 and published in 2000, provide the following values:<ref name=WHO2000>{{cite book | author=World Health Organization | title=Technical report series 894: "Obesity: preventing and managing the global epidemic." | location=Geneva | publisher=World Health Organization | year=2000 | url=http://whqlibdoc.who.int/trs/WHO_TRS_894_(part1).pdf | format=PDF | isbn=92-4-120894-5}}</ref>
* A BMI less than 18.5 is ''underweight''
* A BMI of 18.5–24.9 is ''normal weight''
* A BMI of 25.0–29.9 is ''overweight''
* A BMI of 30.0–34.9 is ''class I obesity''
* A BMI of 35.0-39.9 is ''class II obesity''
* A BMI of > 40.0 is ''class III obesity or severe / morbidly obese''
* A BMI of 35.0 or higher ''in the presence of at least one other significant comorbidity'' is also classified by some bodies as ''morbid obesity''.<ref>{{cite web|url=http://www.nice.org.uk/page.aspx?o=34790 |title=NICE issues guidance on surgery for morbid obesity |accessdate=2007-03-08 |date=19th July 2002 |publisher=National Institute for Health and Clinical Excellence }}</ref><ref>{{cite web| url=http://www.surgery.usc.edu/divisions/cr/bariatricsurgery.html |title=Bariatric Surgery |accessdate=2007-03-08 |date=2006 |work=USC Center for Colorectal and Pelvic Floor Disorders |publisher=University of Southern California }}</ref>
===Waist circumference and waist hip ratio===
{{main|Central obesity}}
BMI does not take into account differing ratios of [[adipose]] to lean tissue; nor does it distinguish between differing forms of adiposity, some of which may correlate more closely with [[cardiovascular]] risk. Increasing understanding of the biology of different forms of adipose tissue has shown that visceral fat or [[central obesity]] (male-type or apple-type obesity, also known as "belly fat") has a much stronger correlation, particularly with [[cardiovascular disease]], than the BMI alone.<ref name=Yusuf2004>{{cite journal | author=Yusuf S, Hawken S, Ounpuu S, Dans T, Avezum A, Lanas F, McQueen M, Budaj A, Pais P, Varigos J, Lisheng L, INTERHEART Study Investigators. | title=Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study|journal=Lancet | year=2004 | pages=937–52 | volume=364 | pmid=15364185 | doi=10.1016/S0140-6736(04)17018-9}}</ref>
The absolute waist circumference (>102 cm in men and >88 cm in women) or [[waist-hip ratio]] (>0.9 for men and >0.85 for women) are both used as measures of central obesity.<ref name=Yusuf2004/>
In a cohort of almost 15,000 subjects from the [[National Health and Nutrition Examination Survey]] (NHANES) III study, waist circumference explained obesity-related health risk significantly better than BMI when [[metabolic syndrome]] was taken as an outcome measure.<ref>{{cite journal |author=Janssen I, Katzmarzyk PT, Ross R |title=Waist circumference and not body mass index explains obesity-related health risk |journal=Am. J. Clin. Nutr. |volume=79 |issue=3 |pages=379–84 |year=2004 |pmid=14985210 |url=http://www.ajcn.org/cgi/content/abstract/79/3/379 |doi=10.1185/030079906X159489}}</ref>
===Other body fat measurements===
An alternative way to determine obesity is to assess percent [[body fat]]. Doctors and scientists generally agree that men with more than 25% body fat and women with more than 30% body fat are obese. However, it is difficult to measure body fat precisely. The most accepted method has been to weigh a person underwater, but underwater weighing is a procedure limited to laboratories with special equipment. Two simpler methods for measuring body fat are the ''skinfold test'', in which a pinch of skin is precisely measured to determine the thickness of the [[subcutaneous]] fat layer; or [[bioelectrical impedance analysis]], usually only carried out at specialist clinics. Their routine use is discouraged.<ref name=NICECG043>{{NICE|43|Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children|2006}}</ref>
Other measurements of body fat include [[computed tomography]] (CT/CAT scan), [[magnetic resonance imaging]] (MRI/NMR), and [[dual energy X-ray absorptiometry]] (DXA). They are mainly used for research purposes.{{fact|date=July 2008}}
===Risk factors and comorbidities===
The presence of risk factors and diseases associated with obesity are also used to establish a clinical diagnosis. [[Coronary heart disease]], [[Diabetes mellitus type 2|type 2 diabetes]], and [[sleep apnea]] are possible life-threatening risk factors that would indicate clinical treatment of obesity.<ref name=NHLBI/> Smoking, hypertension, age and family history are other risk factors that may indicate treatment.<ref name=NHLBI/>
==Effects on health==
===Mortality===
Mortality risk varies with BMI. The lowest risk is found at a BMI of 22-24 kg/m<sup>2</sup> and increases with changes in either direction.<ref>{{cite journal |author=Calle EE, Thun MJ, Petrelli JM, Rodriguez C, Heath CW |title=Body-mass index and mortality in a prospective cohort of U.S. adults |journal=N. Engl. J. Med. |volume=341 |issue=15 |pages=1097–105 |year=1999 |month=October |pmid=10511607 |doi= |url=http://content.nejm.org/cgi/content/full/341/15/1097}}</ref> A BMI of over 32 is associated with a doubling of risk of death.<ref>{{cite journal |author=Manson JE, Willett WC, Stampfer MJ, ''et al'' |title=Body weight and mortality among women |journal=N. Engl. J. Med. |volume=333 |issue=11 |pages=677–85 |year=1995 |pmid=7637744| doi = 10.1056/NEJM199509143331101 <!--Retrieved from CrossRef by DOI bot-->}}</ref>
===Morbidity===
A large number of medical conditions have been associated with obesity. Health consequences are categorised as being the result of either increased fat mass ([[osteoarthritis]], [[obstructive sleep apnea]], social stigma) or increased number of fat cells ([[diabetes mellitus|diabetes]], some forms of [[cancer]], [[cardiovascular disease]], [[non-alcoholic fatty liver disease]]).<ref name=HaslamJames/><ref name=Bray2004>{{cite journal |author=Bray GA |title=Medical consequences of obesity |journal=J. Clin. Endocrinol. Metab. |volume=89 |issue=6 |pages=2583–9 |year=2004 |pmid=15181027 |doi=10.1210/jc.2004-0535}}</ref> There are alterations in the body's response to insulin ([[insulin resistance]]), a [[inflammation|proinflammatory state]] and an increased tendency to [[thrombosis]] (prothrombotic state).<ref name=Bray2004/>
Disease associations may be dependent or independent of the distribution of adipose tissue. [[Central obesity]] (male-type or waist-predominant obesity, characterised by a high waist-hip ratio), is an important risk factor for the ''[[metabolic syndrome]]'', the clustering of a number of diseases and risk factors that heavily predispose for cardiovascular disease. These are [[diabetes mellitus type 2]], [[hypertension|high blood pressure]], [[hypercholesterolemia|high blood cholesterol]], and [[hypertriglyceridemia|triglyceride levels]] ([[combined hyperlipidemia]]).<ref>{{cite journal |author=Grundy SM |title=Obesity, metabolic syndrome, and cardiovascular disease |journal=J. Clin. Endocrinol. Metab. |volume=89 |issue=6 |pages=2595–600 |year=2004 |pmid=15181029 |doi=10.1210/jc.2004-0372}}</ref>
Apart from metabolic syndrome, obesity is related to a variety of other complications. Some are directly caused by obesity, while others are more indirectly related, such as sharing a common cause like poor diet or sedentary lifestyle.
* ''[[Cardiovascular]]'': [[congestive heart failure]], [[cardiomegaly|enlarged heart]] and its associated [[arrhythmia]]s and dizziness, [[varicose veins]], and [[pulmonary embolism]]
*''[[Endocrine]]'': [[polycystic ovarian syndrome]] (PCOS), [[menstruation|menstrual]] disorders, and [[infertility]]<ref name="pmid18077317">{{cite journal |author=van der Steeg JW, Steures P, Eijkemans MJ, ''et al'' |title=Obesity affects spontaneous pregnancy chances in subfertile, ovulatory women |journal=Hum. Reprod. |volume=23 |issue=2 |pages=324–8 |year=2008 |pmid=18077317 |doi=10.1093/humrep/dem371}}</ref>
* ''[[Gastrointestinal]]'': [[gastroesophageal reflux disease]] (GERD), [[non-alcoholic fatty liver disease|fatty liver disease]], [[cholelithiasis]] (gallstones), [[hernia]], and [[colorectal cancer]]
* ''Renal and [[genitourinary]]'': [[erectile dysfunction]],<ref>{{cite journal |author=Esposito K, Giugliano F, Di Palo C, Giugliano G, Marfella R, D'Andrea F, D'Armiento M, Giugliano D |title=Effect of lifestyle changes on erectile dysfunction in obese men: a randomized controlled trial |journal=JAMA |volume=291 |issue=24 |pages=2978–84 |year=2004 |pmid=15213209 |doi=10.1001/jama.291.24.2978}}</ref> [[urinary incontinence]], [[chronic renal failure]],<ref>{{cite journal |author=Ejerblad E, Fored CM, Lindblad P, Fryzek J, McLaughlin JK, Nyrén O |title=Obesity and risk for chronic renal failure |journal=J. Am. Soc. Nephrol. |volume=17 |issue=6 |pages=1695–702 |year=2006 |pmid=16641153 |doi=10.1681/ASN.2005060638}}</ref> [[hypogonadism]] (male), [[breast cancer]] (female), [[endometrial cancer|uterine cancer]] (female), [[stillbirth]]
* ''[[Integument]]'' (skin and appendages): [[stretch mark]]s, [[acanthosis nigricans]], [[lymphedema]], [[cellulitis]], [[carbuncle]]s, [[intertrigo]]
* ''Musculoskeletal'': [[hyperuricemia]] (which predisposes to [[gout]]), immobility, [[osteoarthritis]], [[low back pain]]
* ''Neurologic'': [[stroke]], [[meralgia paresthetica]], [[headache]], [[carpal tunnel syndrome]], [[dementia]],<ref>{{cite journal | author=Whitmer RA, Gunderson EP, Barrett-Connor E, Quesenberry CP Jr, Yaffe K | title=Obesity in middle age and future risk of dementia: a 27 year longitudinal population based study | journal=BMJ | year=2005 | pages=1360 | volume=330 | issue=7504 | pmid=15863436 | doi = 10.1136/bmj.38446.466238.E0 <!--Retrieved from CrossRef by DOI bot-->}}</ref> [[idiopathic intracranial hypertension]]
* ''[[Respiratory system|Respiratory]]'': [[sleep apnea|obstructive sleep apnea]], [[obesity hypoventilation syndrome]], [[asthma]]
* ''[[Psychological]]'': [[Clinical depression|Depression]], low [[self esteem]], [[body dysmorphic disorder]], social stigmatization
* ''[[Cancer]]'': esophageal, colorectal, liver, gallbladder, pancreatic, kidney, non-Hodgkin's lymphoma, multiple myeloma, stomach, prostate cancer, breast, uterus, cervix, and ovary <ref>{{cite journal |author=Calle EE, Rodriguez C, Walker-Thurmond K, Thun MJ |title=Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults |journal=N. Engl. J. Med. |volume=348 |issue=17 |pages=1625–38 |year=2003 |month=April |pmid=12711737 |doi=10.1056/NEJMoa021423 |url=}}</ref>
===Obesity survival paradox===
Although the negative health consequences of obesity in the general population are well support by the available evidence, health outcomes in certain subgroups seem to be improved at an increased BMI, thus leading to the obesity survival paradox.<ref name=Schmidt2007>{{cite journal |author=Schmidt DS, Salahudeen AK |title=Obesity-survival paradox-still a controversy? |journal=Semin Dial |volume=20 |issue=6 |pages=486–92 |year=2007 |pmid=17991192 |doi=10.1111/j.1525-139X.2007.00349.x}}</ref> The paradox was first described in 1999 in overweight and obese patients undergoing [[hemodialysis]]. Since then it has been found in a few other subgroups and explanations for its occurrence have been put forwards.<ref name=Schmidt2007/>
In people with [[heart failure]], those with a BMI between 30.0-34.9 had lower mortality then those with a normal weight. One explanation for this is that people often lose weight as they become progressively more ill.<ref>{{cite journal |author=Habbu A, Lakkis NM, Dokainish H |title=The obesity paradox: fact or fiction? |journal=Am. J. Cardiol. |volume=98 |issue=7 |pages=944–8 |year=2006 |month=October |pmid=16996880 |doi=10.1016/j.amjcard.2006.04.039 |url=}}</ref> This is also seen in those with other types of preexisting heart disease. People with class I obesity do not have greater rates of further cardiac problems over people who have heart disease and are of normal weight. In people with greater degrees of obesity, however, increased rates of heart disease are observed.<ref>{{cite journal |author=Romero-Corral A, Montori VM, Somers VK, ''et al'' |title=Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: a systematic review of cohort studies |journal=Lancet |volume=368 |issue=9536 |pages=666–78 |year=2006 |pmid=16920472 |doi=10.1016/S0140-6736(06)69251-9}}</ref><ref>{{cite journal |author=Oreopoulos A, Padwal R, Kalantar-Zadeh K, Fonarow GC, Norris CM, McAlister FA |title=Body mass index and mortality in heart failure: a meta-analysis |journal=Am. Heart J. |volume=156 |issue=1 |pages=13–22 |year=2008 |month=July |pmid=18585492 |doi=10.1016/j.ahj.2008.02.014 |url=}}</ref> Even after coronary artery bypass graphs ([[CABG]]) no increase in mortality is seen in the overweight and obese. <ref>{{cite journal |author=Oreopoulos A, Padwal R, Norris CM, Mullen JC, Pretorius V, Kalantar-Zadeh K |title=Effect of obesity on short- and long-term mortality postcoronary revascularization: a meta-analysis |journal=Obesity (Silver Spring) |volume=16 |issue=2 |pages=442–50 |year=2008 |month=February |pmid=18239657 |doi=10.1038/oby.2007.36 |url=}}</ref>
==Causes==
Most researchers agree that a combination of excessive calorie consumption and a [[sedentary lifestyle]] are the primary causes of obesity in the majority of the population.<ref>{{cite book | author=Sara Bleich, David Cutler, Christopher Murray, Alyce Adams | title=Working paper 12954: Why is the developed world obese? | publisher=National Bureau of Economic Research | year=2007 | month=March | url=http://www.nber.org/papers/w12954}}</ref> Other less well established or minor influences include genetic causes, medical and psychiatric illnesses, and microbiological causes. A 2006 review identifies ten other possibly underinvestigated causes for recently increasing rates of obesity: (1) insufficient [[sleep]], (2) [[endocrine disruptor]]s - food substances that interfere with lipid metabolism, (3) decreased variability in ambient temperature, (4) decreased rates of [[tobacco smoking|smoking]], which suppresses appetite, (5) increased use of medication that leads to weight gain, (6) increased distribution of ethnic and age groups that tend to be heavier, (7) pregnancy at a later age, (8) intrauterine and intergenerational effects, (9) positive [[natural selection]] of people with a higher BMI, (10) [[assortative mating]], heavier people tending to form relationships with each other.<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 |issue=11 |pages=1585–94 |year=2006 |pmid=16801930 |doi=10.1038/sj.ijo.0803326 |url=http://www.nature.com/ijo/journal/v30/n11/full/0803326a.html}}</ref>
===Dietary===
Despite the widespread availability of nutritional information in schools, doctors' offices, on the internet and on product packaging,<ref>{{cite web | author=National Control for Health Statistics | title=Nutrition For Everyone | publisher=Centers for Disease Control and Prevention | url=http://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_everyone | accesdate=2008-07-09}}</ref> it is evident that overeating remains a substantial problem. In the period of 1971-2000, obesity rates in the United States increased from 14.5% to 30.9% of the population.<ref name=Flegal2002>{{cite journal | author=Flegal KM, Carroll MD, Ogden CL, Johnson CL | title=Prevalence and trends in obesity among US adults, 1999-2000 | journal=JAMA | year=2002 | month=October | volume=288| pages=1723-1727 | url=http://jama.ama-assn.org/cgi/content/full/288/14/1723}}</ref> During the same time, an increase occurred in the average amount of calories consumed. For women, the average increase was 335 calories per day (1542 calories in 1971 and 1877 calories in 2004), while for men the average increase was 168 calories per day (2450 calories in 1971 and 2618 calories in 2004). Most of these extra calories came from an increase in carbohydrate consumption rather than an increase in fat consumption.<ref>{{cite journal | author=Wright JD, Kennedy-Stephenson J, Wang CY, McDowell MA, Johnson CL | title=Trends in intake of energy and macronutrients--United States, 1971-2000 | journal=MMWR Morb Mortal Wkly Rep | year=2004 | month=Feb | volume=53 | issue=4 | pages=80-2 | url=http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5304a3.htm}}</ref> Dietary trends have also change with reliance on [[food energy|energy-dense]] fast-food meals tripling between 1977 and 1995, and calorie intake from fast food quadrupling over the same period.<ref>{{cite book |author=Lin BH, Guthrie J and Frazao E |editor=Frazão E |title=Agriculture Information Bulletin No. 750: America's Eating Habits: Changes and Consequences | url=http://www.ers.usda.gov/publications/aib750/ |year=1999 |publisher=US Department of Agriculture, Economic Research Service |location=Washington, DC |pages=213–239 |chapter=Nutrient contribution of food away from home}}</ref>
===Sedentary lifestyle===
An increasingly [[sedentary lifestyle]] plays a significant role in obesity. There has been a trend toward decreased physical activity due in part to increasingly mechanized forms of work, changing modes of transportation, and increasing urbanization. Studies in children and adults have found a association between the number of hours of television watched and the [[prevalence]] of obesity.<ref>{{cite journal |author=Gortmaker SL, Must A, Sobol AM, Peterson K, Colditz GA, Dietz WH |title=Television viewing as a cause of increasing obesity among children in the United States, 1986-1990 |journal=Arch Pediatr Adolesc Med |volume=150 |issue=4 |pages=356–62 |year=1996 |month=April |pmid=8634729}}</ref><ref>{{cite journal |author=Vioque J, Torres A, Quiles J |title=Time spent watching television, sleep duration and obesity in adults living in Valencia, Spain |journal=Int. J. Obes. Relat. Metab. Disord. |volume=24 |issue=12 |pages=1683–8 |year=2000 |month=December |pmid=11126224 |doi= |url=}}</ref><ref>{{cite journal |author=Tucker LA, Bagwell M |title=Television viewing and obesity in adult females |journal=Am J Public Health |volume=81 |issue=7 |pages=908–11 |year=1991 |month=July |pmid=2053671 |pmc=1405200 |doi= |url=http://www.ajph.org/cgi/reprint/81/7/908 | format=PDF}}</ref> [[school run|Driving one's children to school]] also decreases the amount of exercise that these children get and has led to calls for reduced car use around schools.<ref>{{cite web |author=Caroline Bennett |url=http://www.guardian.co.uk/society/2007/aug/13/health.schools |title=Call to ban cars nears schools to tackle obesity |publication=The Guardian|date=August 13, 2007|accessdate=2008-03-24}}</ref> An association between leasure time activity and obesity has been found. For example in [[Canada]], 27.0% of sedentary men are obese as opposed to 19.6% of active men.<ref name=Tjepkema2005>{{cite book | author=Tjepkema M | chapter=Measured Obesity–Adult obesity in Canada: Measured height and weight | title=Nutrition: Findings from the Canadian Community Health Survey | publisher=Statistics Canada | date=2005-07-06 | location=Ottawa, Ontario | url=http://www.statcan.ca/english/research/82-620-MIE/2005001/articles/adults/aobesity.htm}}</ref>
===Genetics===
Like many other medical conditions, obesity is the result of an interplay between genetic and environmental factors. [[Polymorphism (biology)|Polymorphism]]s in various [[gene]]s controlling [[appetite]], [[metabolism]], and [[adipokine]] release may predispose to obesity when sufficient calories are present. Obesity is a major feature in a number of rare genetic conditions: [[Prader-Willi syndrome]], [[Bardet-Biedl syndrome]], [[MOMO syndrome]], [[leptin receptor]] mutations, [[melanocortin receptor]] mutations. In a people with early-onset severe obesity (defined by an onset before ten years of age and body mass index over three [[standard deviation]]s above normal), 7% harbor a single locus mutation.<ref>{{cite journal |author=Farooqi S, O'Rahilly S |title=Genetics of obesity in humans |journal=Endocr. Rev. |volume=27 |issue=7 |pages=710–18 |year=2006 |month=December |pmid=17122358 |doi=10.1210/er.2006-0040 |url=http://edrv.endojournals.org/cgi/content/full/27/7/710}}</ref> Apart from the above syndromes, an association has been found between an [[FTO gene|''FTO'' gene]] polymorphism and weight. The 16% of adults in the study who were [[homozygous]] for this allele weighed about 3 kilograms more then those who had not inheireted this trait and subsequently had a 1.6 fold greater rate of obesity.<ref>{{cite journal |author=Frayling TM, Timpson NJ, Weedon MN, ''et al'' |title=A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity |journal=Science |volume=316 |issue=5826 |pages=889–94 |year=2007 |pmid=17434869 |doi=10.1126/science.1141634}}</ref> A study of 5092 [[twin|identical twins]] found that childhood obesity has a strong (77%) [[heritability |inherited component]], suggesting that many genetic influences underpinning the development of obesity are yet to be discovered.<ref name="pmid18258631">{{cite journal |author=Wardle J, Carnell S, Haworth CM, Plomin R |title=Evidence for a strong genetic influence on childhood adiposity despite the force of the obesogenic environment |journal=Am. J. Clin. Nutr. |volume=87 |issue=2 |pages=398–404 |year=2008 |pmid=18258631|url=http://www.ajcn.org/cgi/content/full/87/2/398}}</ref>
On a population level, the ''[[thrifty gene hypothesis]]'' postulates that certain ethnic groups may be more prone to obesity when exposed to an equivalent environment. Their ability to take advantage of rare periods of abundance by storing energy as fat would be advantagious during times of varing food availiablity. Individuals with greater adipose reserves would be more likely survive famine. This tendency to store fat however would be maladaptive in societies with stable food supplies.<ref>{{cite journal |author=Chakravarthy MV, Booth FW |title=Eating, exercise, and "thrifty" genotypes: connecting the dots toward an evolutionary understanding of modern chronic diseases |journal=J. Appl. Physiol. |volume=96 |issue=1 |pages=3–10 |year=2004 |pmid=14660491 |doi=10.1152/japplphysiol.00757.2003}}</ref>
===Medical illness===
Certain physical and mental illnesses and the pharmaceutical substances used to treat them can increase one's risk of obesity. Medical illnesses that increase obesity risk include several rare genetic syndromes (listed above) as well as some congenital or acquired conditions: (1) [[hypothyroidism]], (2) [[Cushing's syndrome]], (3) [[growth hormone deficiency]],<ref>{{cite journal |author=Rosén T, Bosaeus I, Tölli J, Lindstedt G, Bengtsson BA |title=Increased body fat mass and decreased extracellular fluid volume in adults with growth hormone deficiency |journal=Clin. Endocrinol. (Oxf) |volume=38 |issue=1 |pages=63–71 |year=1993 |pmid=8435887| doi = 10.1111/j.1365-2265.1993.tb00974.x <!--Retrieved from CrossRef by DOI bot-->}}</ref> and (4) [[eating disorder]]s such [[bulimia nervosa]], [[binge eating disorder]] and [[compulsive overeating]].
Certain medications may cause weight gain and or negative changes in body composition, such as [[glucocorticoids|steroids]], [[atypical antipsychotic]]s, some [[fertility medication]], [[insulin]] and [[sulfonylurea]]s.
===Microbiological===
The role of [[bacteria]] colonizing the digestive tract in the development of obesity has recently become the subject of investigation. Bacteria participate in digestion (especially of [[fatty acid]]s and [[polysaccharide]]s), and alterations in the proportion of particular strains of bacteria may explain why certain people are more prone to weight gain than others. Human digestive tract bacteria are generally either members of the phyla of [[bacteroidetes]] or of [[firmicutes]]. In obese people, there is a relative abundance of firmicutes (which cause relatively high energy absorption), which is restored by weight loss. From these results it cannot be concluded whether this imbalance is the cause or effect of obesity.<ref>{{cite journal |author=Ley RE, Turnbaugh PJ, Klein S, Gordon JI |title=Microbial ecology: human gut microbes associated with obesity |journal=Nature |volume=444 |issue=7122 |pages=1022–3 |year=2006 |pmid=17183309 |doi=10.1038/4441022a}}</ref>
===Social determinants===
The correlation between [[social class|social class]] and BMI is inconsistent. Comparing net worth with BMI shows that obese Americans are approximately half as wealthy as thin ones. When income differentials are factored out, the inequity persisted. A tendency to rely on [[fast food]] is seen as one of the reasons why this result occured.<ref>{{cite journal | author=Zagorsky JL | title=Is obesity as dangerous to your wealth as to your health? | journal=Res Aging | year=2004 | volume=26 | pages=130-152 | doi=10.1177/0164027503258519}}<!--No PMID--></ref>Another study found women who married into a higher social class are thinner than women who married into a lower social class.{{fact | date=July 2008}} In contrast, the 2004 Canadian Community Health Survey found the exact oposite: men from lower middle income households were less likely to be obese than were those in the highest income households and women from middle income households had the highest rates of obesity.<ref name=Tjepkema2005/>
A study of 12,067 people followed for 32 years found a correlation in BMI change between friends, siblings, and spouses. This was irrespective of geographical distance. The authors concluded that acceptance of body mass by people in one's life plays an important role in changes in body size.<ref>{{cite journal |author=Christakis NA, [[James H. Fowler|Fowler JH]] |title=The Spread of Obesity in a Large Social Network over 32 Years |journal= New England Journal of Medicine|volume=357 |issue=4 |pages=370–379 |year=2007 |pmid=17652652 |doi=10.1056/NEJMsa066082}}</ref>
Cessation of smoking verse continued smoking can leads to weight gain. A study found that those who quit smoking gained 4-5 kilograms over ten years. One sixth of the rise in obesity in North Americans can be attributed to falling rates of smoking . <ref>{{cite journal |author=Flegal KM, Troiano RP, Pamuk ER, Kuczmarski RJ, Campbell SM |title=The influence of smoking cessation on the prevalence of overweight in the United States |journal=N. Engl. J. Med. |volume=333 |issue=18 |pages=1165–70 |year=1995 |month=November |pmid=7565970 |doi= |url=http://content.nejm.org/cgi/content/full/333/18/1165}}</ref>
==Neurobiological mechanisms==
[[Image:Fatmouse.jpg|thumb|350px|Scientists investigating the mechanisms and treatment of obesity may use [[animal model]]s such as [[mouse|mice]] to conduct experiments.]]
Flier<ref name="flier">{{cite journal | author=Flier JS | title=Obesity wars: molecular progress confronts an expanding epidemic | journal=Cell | year=2004 | pages=337–50 | volume=116 | issue=2 | pmid=14744442 | doi = 10.1016/S0092-8674(03)01081-X <!--Retrieved from CrossRef by DOI bot-->}}</ref> summarizes the many possible [[pathophysiology|pathophysiological]] mechanisms involved in the development and maintenance of obesity. This field of research had been almost unapproached until [[leptin]] was discovered in 1994. Since this discovery, many other hormonal mechanisms have been elucidated that participate in the regulation of [[appetite]] and food intake, storage patterns of [[adipose tissue]], and development of [[insulin resistance]]. Since leptin's discovery, [[ghrelin]], [[orexin]], [[PYY 3-36]], [[cholecystokinin]], [[adiponectin]], and many other mediators have been studied. The [[adipokine]]s are mediators produced by adipose tissue; their action is thought to modify many obesity-related diseases.
Leptin and ghrelin are considered to be complementary in their influence on appetite, with ghrelin produced by the [[stomach]] modulating short-term appetitive control (i.e. to eat when the stomach is empty and to stop when the stomach is stretched). Leptin is produced by adipose tissue to signal fat storage reserves in the body, and mediates long-term appetitive controls (i.e. to eat more when fat storages are low and less when fat storages are high). Although administration of leptin may be effective in a small subset of obese individuals who are leptin deficient, most obese individuals are thought to be leptin resistant and have been found to have high levels of leptin.<ref>{{cite journal |author=Hamann A, Matthaei S |title=Regulation of energy balance by leptin |journal=Exp. Clin. Endocrinol. Diabetes |volume=104 |issue=4 |pages=293–300 |year=1996 |pmid=8886745 |doi= |url=}}</ref>. This resistance is thought to explain in part why administration of leptin has not been shown to be effective in suppressing appetite in most obese subjects.<ref name="flier"/>
While leptin and ghrelin are produced peripherally, they control appetite through their actions on the [[central nervous system]]. In particular, they and other appetite-related hormones act on the [[hypothalamus]], a region of the brain central to the regulation of food intake and energy expenditure. There are several circuits within the hypothalamus that contribute to its role in integrating appetite, the [[melanocortin]] pathway being the most well understood.<ref name="flier"/> The circuit begins with an area of the hypothalamus, the [[arcuate nucleus]], that has outputs to the [[lateral hypothalamus]] (LH) and [[ventromedial hypothalamus]] (VMH), the brain's feeding and satiety centers, respectively.<ref>{{cite book |author=Boulpaep, Emile L.; Boron, Walter F. |title=Medical physiology: a cellular and molecular approach |publisher=Saunders |location=Philadelphia |year=2003 |pages= |isbn=0-7216-3256-4 |oclc= |doi=}}</ref>
The arcuate nucleus contains two distinct groups of [[neuron]]s.<ref name="flier"/> The first group coexpresses [[neuropeptide Y]] (NPY) and [[agouti-related peptide]] (AgRP) and has stimulatory inputs to the LH and inhibitory inputs to the VMH. The second group coexpresses [[pro-opiomelanocortin]] (POMC) and [[cocaine- and amphetamine-regulated transcript]] (CART) and has stimulatory inputs to the VMH and inhibitory inputs to the LH. Consequently, NPY/AgRP neurons stimulate feeding and inhibit satiety, while POMC/CART neurons stimulate satiety and inhibit feeding. Both groups of arcuate nucleus neurons are regulated in part by leptin. Leptin inhibits the NPY/AgRP group while stimulating the POMC/CART group. Thus a deficiency in leptin signaling, either via leptin deficiency or leptin resistance, leads to overfeeding and may account for some genetic and acquired forms of obesity.<ref name="flier"/>
== Treatment ==
{{Main|Weight loss#Intentional weight loss|l1=Weight loss}}
The main treatment for obesity consists of [[dieting|eating less]] and [[Physical exercise|exercising]] more. Diet programs may produce weight loss over the short term,<ref name=Strychar>{{cite journal |author=Strychar I |title=Diet in the management of weight loss |journal=CMAJ |volume=174 |issue=1 |pages=56–63 |year=2006 |month=January |pmid=16389240 |pmc=1319349 |doi=10.1503/cmaj.045037 |url=http://www.cmaj.ca/cgi/content/full/174/1/56}}</ref> but keeping this weight off can be a problem. It often requires making [[Physical exercise|exercise]] and a [[Healthy diet|lower calorie diet]] a permanent part of a person's lifestyle.<ref>{{cite journal |author=Shick SM, Wing RR, Klem ML, McGuire MT, Hill JO, Seagle H |title=Persons successful at long-term weight loss and maintenance continue to consume a low-energy, low-fat diet |journal=J Am Diet Assoc |volume=98 |issue=4 |pages=408–13 |year=1998 |month=April |pmid=9550162 |doi=10.1016/S0002-8223(98)00093-5}}</ref><ref>{{cite journal |author=Tate DF, Jeffery RW, Sherwood NE, Wing RR |title=Long-term weight losses associated with prescription of higher physical activity goals. Are higher levels of physical activity protective against weight regain? |journal=Am. J. Clin. Nutr. |volume=85 |issue=4 |pages=954–9 |year=2007 |month=April |pmid=17413092 |url=http://www.ajcn.org/cgi/content/full/85/4/954}}</ref>In the general population only 20% are successful at long-term weight loss maintenance.<ref>{{cite journal |author= |title=Science-Based Solutions to Obesity: What are the Roles of Academia, Government, Industry, and Health Care? Proceedings of a symposium, Boston, Massachusetts, USA, March 10-11, 2004 and Anaheim, California, USA, October 2, 2004 |journal=Am. J. Clin. Nutr. |volume=82 |issue=1 Suppl |pages=207S–273S |year=2005 |month=July |pmid=16106572 |url=http://www.ajcn.org/cgi/content/full/82/1/222S}}</ref> In a more structured setting, however, 67% of people who lost greater then 10% of their body mass maintained or continued to lose weight one year later.<ref>{{cite journal |author=Weiss EC, Galuska DA, Kettel Khan L, Gillespie C, Serdula MK |title=Weight regain in U.S. adults who experienced substantial weight loss, 1999-2002 |journal=Am J Prev Med |volume=33 |issue=1 |pages=34–40 |year=2007 |month=July |pmid=17572309 |doi=10.1016/j.amepre.2007.02.040 |url=}}</ref> An average maintained weight lose of more then 3 kg or 3% of total body mass could be sustained for five years.<ref>{{cite journal |author=Anderson JW, Konz EC, Frederich RC, Wood CL |title=Long-term weight-loss maintenance: a meta-analysis of US studies |journal=Am. J. Clin. Nutr. |volume=74 |issue=5 |pages=579–84 |year=2001 |month=November |pmid=11684524 |url=http://www.ajcn.org/cgi/content/full/74/5/579}}</ref> There are significant benefits to weight loss. In a [[prospective]] study, intentional weight loss of any amount was associated with a 20% reduction in all-cause mortality.<ref>{{cite journal |author=Williamson DF, Pamuk E, Thun M, Flanders D, Byers T, Heath C |title=Prospective study of intentional weight loss and mortality in never-smoking overweight US white women aged 40-64 years |journal=Am. J. Epidemiol. |volume=141 |issue=12 |pages=1128–41 |year=1995 |month=June |pmid=7771451}}</ref>
=== Diet ===
{{main|Dieting}}
Diets to promote weight lose are general divided into four categories low-calorie, low-fat, low-carbohydrate, and very low calorie.<ref name=Strychar/>
Low calorie diets usually produce an energy deficit of 500 - 1000 calories per day, which can result in a 0.5 kilogram weight loss per week. They include the [[DASH diet]] and [[Weight Watchers]] among others. The National Institutes of Health reviewed 34 randomized controlled trials to determine the effectiveness of low-calorie diets. They found that these diet lowered total body mass by 8% over 3-12 months.<ref name=Strychar/>
Low fat diets involve the reduction of the percentage of fat in ones diet. Calorie consumption is reduced but not purposely so. Diets of this type include NCEP Step I and II. A meta-analysis of 16 trials of 2–12 months duration found that low-fat diets resulted in weight loss of 3.2 kg over eating as normal.<ref name=Strychar/>
Low carbohydrate diets are relatively high in fat and protein. They are very popular in the press however are not recommenced by the American Heart Association. Diets of this type include Atkins and Protein Power. A review of 94 trials found that weight loss was associated with decreased calorie consumption rather then any special properties of reduced carbohydrate consumption. No adverse affect from low carbohydrate diets were detected.<ref>{{cite journal |author=Bravata DM, Sanders L, Huang J, ''et al'' |title=Efficacy and safety of low-carbohydrate diets: a systematic review |journal=JAMA |volume=289 |issue=14 |pages=1837–50 |year=2003 |month=April |pmid=12684364 |doi=10.1001/jama.289.14.1837 |url=}}</ref>
A further meta-analysis of 6 randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies.<ref name=Strychar/>
Very low calorie diets maintain protein intake well limiting calories from both fat and carbohydrates. They subject the body to starvation and produce average weekly weight loss of 1.5–2.5 kilograms. These diets are not recommended for general use as they are associated with adverse side effect such as lose of lean muscle mass, increased risks of gout, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications. <ref name=Strychar/>
=== Exercise ===
{{Main|Physical exercise}}
With use, muscles consume energy derived from both fat and glycogen. Due to the large size of leg muscles walking, running, and cycling are the most effective means of exercise to reduce body fat.{{fact|date=July 2008}}
A [[meta-analysis]] of 43 [[randomized controlled trials]] by the [[Cochrane Collaboration]] found that exercising alone led to limited weight loss. In combination with diet, however, it resulted in a 1 kilogram weight loss over dieting alone. A 1.5 kilograms loss was observed with a greater degree of exercise.<ref name="pmid17054187">{{cite journal |author=Shaw K, Gennat H, O'Rourke P, Del Mar C |title=Exercise for overweight or obesity |journal=Cochrane database of systematic reviews (Online) |volume= |issue=4 |pages=CD003817 |year=2006 |pmid=17054187 |doi=10.1002/14651858.CD003817.pub3}}</ref> Even though exercise as carried out in the general population has only modest effects a dose response curve is found and very intense exercise can lead to substantial weight lose. During 20 weeks of basic military training with no dietary restriction obese military recruit lost 12.5 kg.<ref>{{cite journal |author=Lee L, Kumar S, Leong LC |title=The impact of five-month basic military training on the body weight and body fat of 197 moderately to severely obese Singaporean males aged 17 to 19 years |journal=Int. J. Obes. Relat. Metab. Disord. |volume=18 |issue=2 |pages=105–9 |year=1994 |month=February |pmid=8148923 |doi= |url=}}</ref><ref>http://www.uptodate.com/online/content/topic.do?topicKey=obesity/6876&selectedTitle=9~150&source=search_result#8</ref>
===Drugs===
{{main|Anti-obesity drug}}
Medication most commonly prescribed for diet/exercise-resistant obesity is [[orlistat]] (Xenical, which reduces intestinal fat absorption by inhibiting [[pancreas|pancreatic]] [[lipase]]) and [[sibutramine]] (Reductil, Meridia, an [[anorectic]]). Weight loss with these drugs is modest, and over the longer term average weight loss on orlistat is 2.9 kg, sibutramine 4.2 kg and rimonabant 4.7 kg. Orlistat and rimonabant lead to a reduced incidence of diabetes, and all drugs have some effect on [[lipoprotein]]s (different forms of [[cholesterol]]). There is little data, however, on longer-term complications of obesity such as [[myocardial infarction|heart attacks]]. All drugs have side-effects and potential contraindications.<ref>{{cite journal |author=Rucker D, Padwal R, Li SK, Curioni C, Lau DC |title=Long term pharmacotherapy for obesity and overweight: updated meta-analysis |journal=BMJ |volume=335 |issue=7631 |pages=1194–9 |year=2007 |pmid=18006966 |doi=10.1136/bmj.39385.413113.25 |unused_data=|http://www.bmj.com/cgi/content/full/335/7631/1194}}</ref> It is common for weight loss drugs to be tried for a period of time (e.g. 3 months), and to discontinue them or change to another agent if no benefit is achieved, such as weight loss less than 5% the total body weight.<ref name=NICECG043/>
A [[meta-analysis]] of [[randomized controlled trials]] by the international [[Cochrane Collaboration]] concluded that in ''diabetic'' patients fluoxetine, orlistat and sibutramine could achieve significant but modest weight loss over 12-57 weeks, with long-term health benefits being unclear.<ref name="pmid15674929">{{cite journal |author=Norris SL, Zhang X, Avenell A, Gregg E, Schmid CH, Lau J |title=Pharmacotherapy for weight loss in adults with type 2 diabetes mellitus |journal=Cochrane database of systematic reviews (Online) |volume= |issue=1 |pages=CD004096 |year=2005 |pmid=15674929 |doi=10.1002/14651858.CD004096.pub2}}</ref>
Obesity may also influence the choice of drug treatment for diabetes. [[Metformin]] may lead to mild weight reduction (as opposed to [[sulfonylurea]]s and [[insulin]]), and has been demonstrated to reduce the risk of [[cardiovascular disease]] in type 2 diabetics who are obese.<ref name = UKPDS>{{cite journal | author =UK Prospective Diabetes Study (UKPDS) Group | title = Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34) | journal = Lancet | volume = 352 | issue = 9131 | pages = 854–65 | year = 1998 | pmid=9742977 |doi=10.1016/S0140-6736(98)07037-8}}</ref> The [[thiazolidinedione]]s may cause slight weight gain, but decrease the "pathologic" form of abdominal fat and may therefore be used in diabetics with central obesity.<ref>{{cite journal |author=Fonseca V |title=Effect of thiazolidinediones on body weight in patients with diabetes mellitus |journal=Am. J. Med. |volume=115 Suppl 8A |issue= |pages=42S–48S |year=2003 |pmid=14678865 |doi=10.1016/j.amjmed.2003.09.005}}</ref>
===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. Weight loss surgery relies on various principles; 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]]) while others also reduce the length of bowel that food will be in contact with, directly reducing absorption ([[gastric bypass surgery]]). Band surgery is reversible, while bowel shortening operations are not. Some procedures can be performed [[laparoscopic surgery|laparoscopically]]. Complications from weight loss surgery are frequent.<ref name="pmid16862031">{{cite journal |author=Encinosa WE, Bernard DM, Chen CC, Steiner CA |title=Healthcare utilization and outcomes after bariatric surgery |journal=Medical care |volume=44 |issue=8 |pages=706–12 |year=2006 |pmid=16862031 |doi=10.1097/01.mlr.0000220833.89050.ed}}</ref>
Two large studies have demonstrated a mortality benefit from bariatric surgery. A marked decrease in the risk of [[diabetes mellitus]], [[cardiovascular disease]] and [[cancer]] has been found.<ref name="pmid17715408">{{cite journal |author=Sjöström L, Narbro K, Sjöström CD, ''et al'' |title=Effects of bariatric surgery on mortality in Swedish obese subjects |journal=N. Engl. J. Med. |volume=357 |issue=8 |pages=741–52 |year=2007 |pmid=17715408 |doi=10.1056/NEJMoa066254}}</ref><ref name="pmid17715409">{{cite journal |author=Adams TD, Gress RE, Smith SC, ''et al'' |title=Long-term mortality after gastric bypass surgery |journal=N. Engl. J. Med. |volume=357 |issue=8 |pages=753–61 |year=2007 |pmid=17715409 |doi=10.1056/NEJMoa066603}}</ref> Weight loss was most marked in the first few months after surgery, but the benefit was sustained in the longer term. In one study there was an unexplained increase in deaths from accidents and suicide that did not outweigh the benefit in terms of disease prevention. Gastric bypass surgery was about twice as effective as banding procedures.<ref name="pmid17715409"/>
=== Clinical protocols ===
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 | pmid=15809464}} [http://www.annals.org/cgi/content/full/142/7/525 Fulltext].</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.
# 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]].
# 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.
# 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 = 10.1016/S0749-3797(02)00580-9}}</ref>
== Prevalence ==
{{worldwide}}
[[Image:bmi30chart.png|thumb|250px|Comparison of obesity as a percentages of total population in [[Organisation for Economic Co-operation and Development|OECD]] member countries.]]
As of 2005 the World Health Organization estimates that globally at least 400 million adults are obese.<ref name=WHO2000/> Once considered only a problem in high-income countries, rate of obesity are rising world wide. These increases have been felt most dramatically in urban settings.<ref name=WHO2000/>
;[[Australia]]
Studies conducted in 2006 found that close to 52% of Australian women and up to 67% of Australian men aged 25 or over are [[overweight]] or obese. <ref>{{cite web |url=http://www.health.nsw.gov.au/obesity/adult/about.html |title=Childhood Obesity |accessdate=2008-06-22 |date=2006-08-03 |publisher=[[Government of New South Wales]] }}</ref>
;[[Canada]]
The number of Canadians who are obese has risen dramatically in recent years. In 2004, direct measurements of height and weight found 23.1% of Canadians older then 18 had a BMI greater then 30. When broken down into degrees of obesity 15.2% were Class I (BMI 30–34.9), 5.1% were Class II (BMI 35–39.9), and 2.7%, Class III (BMI > 40). This is in contrast to self reported data the year previous of 15.2% and in 1978/1979 of 13.8%. The greatest increases occurred among the more severe degrees of obesity, Class III obesity increased from 0.9% to 2.7% from 1978/1979 to 2004. Obesity in Canada varies by ethnicity with people of Aboriginal origin having a significantly higher rate of obesity rate (37.6%) then the national average.<ref name=Tjepkema2005/>
;[[People's Republic of China|China]]
Because of the booming economy increasing average incomes, the population of [[China]] has recently begun a more sedentary lifestyle and at the same time begun consuming more calorie-rich foods. From 1991 to 2004 the percentage of adults who are overweight or obese increased from 12.9% to 27.3%.<ref>{{cite news |first=Barry |last= Popkin |authorlink= |coauthors= |title= The World Is Fat |url= |id= {{ISSN|0036-8733}} |pages= 94 |publisher= Scientific American |accessdate= |date=September, 2007}}</ref>
;[[United Kingdom]]
The Health Survey for England predicts that more than 12 million adults and 1 million children will be obese by 2010 if no action is taken.<ref>BBC [http://news.bbc.co.uk/1/hi/health/5282446.stm England to have 13 m obese by 2010] [[25 August]] [[2006]]</ref><ref>[http://www.dh.gov.uk/PublicationsAndStatistics/Publications/PublicationsStatistics/PublicationsStatisticsArticle/fs/en?CONTENT_ID=4138630&chk=XVZ/60 Forecasting obesity to 2010]</ref>
;[[United States]]
The prevalence of overweight and obesity in the United States makes obesity a leading public health problem. The United States has the highest rates of obesity in the [[developed world]].<ref>According to circa 2005 [[OECD]] data. See [http://titania.sourceoecd.org/vl=13245990/cl=31/nw=1/rpsv/health2007/3-3.htm §3.3, Overweight and obesity, ''Health at a Glance 2007: OECD Indicators''], SourceOECD (accessed on line [[January 12]], [[2008]].)</ref> From 1980 to 2002, obesity has doubled in adults and overweight prevalence has tripled in children and adolescents.<ref name="pmid16595758">{{cite journal |author=Ogden CL, Carroll MD, Curtin LR, McDowell MA, Tabak CJ, Flegal KM |title=Prevalence of overweight and obesity in the United States, 1999-2004 |journal=JAMA |volume=295 |issue=13 |pages=1549–55 |year=2006 |pmid=16595758 |doi=10.1001/jama.295.13.1549}}</ref> From 2003-2004, "children and adolescents aged 2 to 19 years, 17.1% were overweight... and 32.2% of adults aged 20 years or older were obese."<ref name="pmid16595758"/> In 2005 it was reported that currently, about 119 million, or 64.5%, of US adults are either overweight or obese.<ref name = "BBC-health">{{cite web |url=http://news.bbc.co.uk/1/hi/health/4183086.stm |title=US people getting fatter, fast |work=BBC NEWS, Health | date=2005-08-25 |accessdate=2008-07-16}}</ref>
Obesity is a public health and policy problem because of its prevalence, costs and burdens.<ref>{{cite book | author=Satcher D | title=The Surgeon General's Call to Action to Prevent and Decrease Overweight and Obesity | year=2001 | publisher=U.S. Dept. of Health and Human Services, Public Health Service, Office of Surgeon General | url=http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hstat5.chapter.2 | isbn=0-16051-005-8}}</ref> The prevalence of obesity has been continually rising for two decades.<ref>Centers for Disease Control and Prevention, U.S. Obesity Trends 1984 - 2002 [http://www.cdc.gov/nccdphp/dnpa/obesity/trend/maps/index.htm].</ref> This sudden rise in obesity prevalence is attributed to environmental and population factors rather than individual behavior and biology because of the rapid and continual rise in the number of overweight and obese individuals.<ref>{{cite journal |author=Morrill AC, Chinn CD |title=The obesity epidemic in the United States |journal=J Public Health Policy |volume=25 |issue=3-4 |pages=353–66 |year=2004 |pmid=15683071}}</ref>
==Historical and cultural perspectives==
{{Wikinewscat|Obesity}}
===Etymology===
''Obesity'' is the nominal form of ''obese'' which comes from the [[Latin]] ''obēsus'', which means "stout, fat, or plump." ''Ēsus'' is the past participle of ''edere'' (to eat), with ''ob'' added to it. In [[Classical Latin]], this verb is seen only in past participial form. Its first attested usage in [[English language|English]] was in 1651, in [[Noah Biggs]]'s ''Matæotechnia Medicinæ Praxeos''.<ref>''[[The Oxford English Dictionary]]'' (website)</ref>
===History===
{{Cleanup|date=October 2007}}
[[Image:Italienischer Maler des 17. Jahrhunderts 001.jpg|110px|thumb|Obesity was a status symbol in European culture: "The Tuscan General" by Alessandro del Borro, 17th century.]]
In several human cultures, obesity was associated with [[physical attractiveness]], [[physical strength|strength]], and [[fertility]]. Some of the earliest known cultural [[artifact (archaeology)|artifact]]s, known as [[Venus figurines]], are pocket-sized [[statue]]ttes representing an obese female figure. Although their cultural significance is unrecorded, their widespread use throughout pre-historic Mediterranean and European cultures suggests a central role for the obese female form in [[magic and religion|magical]] rituals, and suggests cultural approval of (and perhaps reverence for) this body form. This is most likely due to their perceived ability to easily bear children and survive [[famine]].{{fact|date=July 2008}}
This was especially the case in the visual arts, such as the paintings of [[Peter Paul Rubens|Rubens]] (1577–1640), whose regular depiction of fat women gives us the description ''Rubenesque''. Obesity can also be seen as a symbol within a system of prestige. "The kind of food, the quantity, and the manner in which it is served are among the important criteria of social class. In most tribal societies, even those with a highly stratified social system, everyone – royalty and the commoners – ate the same kind of food, and if there was famine everyone was hungry. With the ever increasing diversity of foods, food has become not only a matter of social status, but also a mark of one's personality and taste."<ref>{{cite book | author=Powdermaker H | chapter=An anthropological approach to the problem of obesity | title=Food and Culture: A Reader | editor=Penny van Esterik and Carole Counihan | location=New York | publisher=Routledge | year=1997 | pages=206 | isbn=0-415-91710-7}}</ref>
As [[food security]] was realized, obesity came to serve more as a visible signifier of "lust for life", appetite, and immersion in the realm of the [[eroticism|erotic]].{{fact|date=July 2008}}
===Contemporary culture===
In modern Western culture, the obese body shape is widely regarded as unattractive and many negative stereotypes are commonly associated with obese people. Obese children, teenagers and adults can also face a heavy social stigma. Obese children are frequently the targets of bullies and are often shunned by their peers. Although obesity rates are rising amongst all social classes in the West, obesity is often seen as a sign of lower [[socio-economic status]].<ref>{{cite book |author=Critser, Greg |title=Fat Land |publisher=Penguin Books Ltd |location=London, England |year=2004 |pages= |isbn=0-14-101540-3}}</ref> Most obese people have experienced negative thoughts about their body image, and some take drastic steps to try to change their shape including the use of stimulants and [[bariatrics|surgery]].{{fact | date=July 2008}}
Not all contemporary cultures disapprove of obesity. There are many cultures which are traditionally more approving (to varying degrees) of obesity, including some African, Arabic, Indian, and Pacific Island cultures. Especially in recent decades, obesity has come to be seen more as a medical condition in modern Western culture even being referred to as an epidemic.<ref>{{cite news | last = Phillips | first = Stone | coauthors = | title = Who's to blame for the U.S. obesity epidemic? | work = | pages = | language = [[English language|English]] | publisher = [[MSNBC]] | date = [[2006-08-18]] | url = http://www.msnbc.msn.com/id/14415766/ | accessdate = 2007-06-03 }}</ref>
A small but vocal [[fat acceptance movement]] seeks to challenge the established relationship between obesity and health outcomes. Obesity advocacy groups have initiated litigation to defend the rights of obese people. Some notable figures within this movement, such as [[Paul Campos]], argue that the social stigma surrounding obesity is the problem and that health risks associated with obesity are a conspiracy.<ref>{{cite book |author=Campos, Paul F. |title=The Diet Myth |publisher=Gotham |location= |year=2005 |pages= |isbn=1-59240-135-X}}</ref>
===Popular culture===
[[Image:Idiocracy movie poster.jpg|thumb|150|The theatrical poster for the film ''[[Idiocracy]]'', a movie set in the distant future, features an obese version of Da Vinci's [[Vitruvian Man]].]]
{{Original research|section|date=December 2007}}
Various [[stereotype]]s of obese people have found their way into expressions of [[popular culture]]. A common stereotype is the obese character who has a warm and dependable personality, or a jolly fat man like [[Santa Claus]]. Equally common is the obese vicious bully (such as [[Dursley Family#Dudley Dursley|Dudley Dursley]] from the [[Harry Potter]] book series, [[Eric Cartman]] from ''[[South Park]]'', [[Nelson Muntz]] from ''[[The Simpsons]]'').{{fact | date=July 2008}}
[[Gluttony]] and obesity are commonly depicted together in works of fiction.{{fact | date=July 2008}}
In cartoons, obesity is often used to comedic effect, with fat animal characters (such as [[Piggy (Merrie Melodies)|Piggy]], [[Porky Pig]], [[Disney's Adventures of the Gummi Bears#Main characters|Tummi Gummi]], and [[Rupert (TV series)#Voice actors and their characters|Podgy Pig]]) having to squeeze through narrow spaces, frequently getting stuck or even exploding.{{fact | date=July 2008}}
A more unusual example of obesity-related humour is [[Bustopher Jones]], from [[T. S. Eliot]]'s poem "Bustopher Jones: The Cat About Town" featured in ''[[Old Possum's Book of Practical Cats]]'', and the musical ''[[Cats (musical)|Cats]]'' derived from the poem. Bustopher's claim to fame is that he is a regular visitor to many [[gentlemen's clubs]] including [[Drones]], Blimp's and the Tomb. Due to his constant lunching at these clubs, he is remarkably fat, being described by others as "a twenty-five pounder... And he's putting on weight everyday." Another popular character, [[Garfield]], a cartoon cat, is also obese for humor. When his owner, Jon, puts him on diets, rather than losing weight, Garfield slows down his weight gain.{{fact | date=July 2008}}
It can be argued that depiction in popular culture adds to and maintains commonly perceived stereotypes, in turn harming the [[self esteem]] of obese people {{weasel-inline}}. On the other hand, obesity is often associated with positive characteristics such as good humor. In addition, some people are [[sexual attraction|sexually attracted]] to obese people (see [[chubby culture]] and [[fat admirer]]).{{fact | date=July 2008}}
==Public health and policy==
===Environmental factors===
While it may often appear obvious why a certain individual gets fat, it is far more difficult to understand why the average weight of certain societies have recently been growing. While genetic causes are central to understanding obesity, they cannot fully explain why one culture grows fatter than another.{{fact | date=July 2008}}
This is most notable in the [[United States]]. In the years from just after the [[Second World War]] until 1960 the average person's weight increased, but few were obese. In the two and a half decades since 1980 the growth in the rate of obesity has accelerated markedly and is increasingly becoming a [[public health]] concern.<ref name = "BBC-health"/>
There are a number of theories as to the cause of this change since 1980. Most believe it is a combination of various factors.
*''Lack of activity'': obese people are less active in general than lean people, and not just because of their obesity. A controlled increase in calorie intake of lean people did not make them less active; correspondingly when obese people lost weight they did not become more active. Weight change does not affect activity levels, but the converse seems to be the case.<ref>{{cite journal | author=Levine JA, Lanningham-Foster LM, McCrady SK, Krizan AC, Olson LR, Kane PH, Jensen MD, Clark MM | title=Interindividual variation in posture allocation: possible role in human obesity | journal=Science | year=2005 | pages=584–6 | volume=307 | issue=5709 | pmid=15681386 | doi=10.1126/science.1106561}}</ref>
*''Lower relative cost of foodstuffs'': massive changes in agricultural policy in the United States and Europe have led to food prices for consumers being lower than at any point in history. This can raise costs for consumers in some areas but greatly lower it in others. Current debates into trade policy highlight disagreements on the effects of subsidies. In the United States, production of [[corn]], [[soy]], [[wheat]] and [[rice]] is [[subsidy|subsidized]] through the [[U.S. farm bill]]. Corn and soy, which are main sources of the sugars and fats in processed food, are thus cheap compared to fruits and vegetables.<ref>{{cite news|author=Pollan, Michael|title=You Are What You Grow|work=New York Times|url=http://www.nytimes.com/2007/04/22/magazine/22wwlnlede.t.html?ex=1186027200&en=bbe0f6a2c10e3b3c&ei=5070|date= April 22, 2007|accessdate= 2007-07-30}}</ref>
*''Increased marketing'' has also played a role. In the early 1980s in America the [[Ronald Reagan|Reagan]] administration lifted most regulations pertaining to sweets and [[fast food advertising]] to children. As a result, the number of advertisements seen by the average child increased greatly, and a large proportion of these were for [[fast food]] and [[sweets]].<ref> [[Brian Wansink]] and [[Mike Huckabee]] (2005), “De-Marketing Obesity,” California Management Review, 47:4 (Summer), 6-18.</ref>
*The ''changing workforce'' as each year a greater percent of the population spends their entire workday behind a desk or [[computer]], seeing virtually no exercise. In the [[kitchen]] the [[microwave oven]] has seen sales of calorie-dense [[frozen food|frozen convenience foods]] skyrocket and has encouraged more elaborate [[snack]]ing{{Fact|date=August 2007}}.
*A social cause that is believed by many to play a role is the increasing number of ''two income households'' in which one parent no longer remains home to look after the house. This increases the number of [[restaurant]] and [[take-out]] meals{{Fact|date=August 2007}}.
*''[[Urban sprawl]]'' may be a factor: obesity rates increase as urban sprawl increases, possibly due to less walking and less time for cooking.<ref>{{cite journal | author=Lopez R | title=Urban sprawl and risk for being overweight or obese | journal=Am J Public Health | year=2004 | pages=1574–9 | volume=94 | issue=9 | pmid=15333317}}</ref>
*Since 1980 ''[[fast food]] [[restaurant]]s'' have seen dramatic growth in terms of the number of outlets and customers served. Low food costs, and intense competition for market share, led to increased portion sizes—for example, [[McDonalds]] [[french fries]] portions rose from 200 calories (840 [[joule|kilojoules]]) in 1960 to over 600 calories (2,500 kJ) today{{Fact|date=August 2007}}.
===Public health and policy responses===
[[Image:Wide Chair.jpg|thumb|250px|Some [[United States|U.S.]] [[Kaiser Permanente]] facilities now provide oversized chairs such as this one at [[Richmond Medical Center]] for obese patients.]]
Public health and policy responses to obesity seek to understand and correct the environmental factors responsible for shifts in the prevalence of overweight and obesity in a population. Obesity and overweight are, currently, primarily policy problems in the United States.{{Fact|date=August 2007}} Policy and public health solutions look to change the environmental factors that promote calorie dense, low nutrient food consumption and that inhibit physical activity.{{Fact|date=August 2007}}
In the United States, policy has focused primarily on controlling [[childhood obesity]] which has the most serious long-term public health implication. Efforts have been underway to target schools. There are efforts underway to reform federally-reimbursed meal programs, limit food marketing to children, and ban or limit access to sugar sweetened beverages. In Europe, policy has focused on limiting marketing to children. There has been international focus on sugar policy and the role of agriculture policy in producing food environments that produce overweight and obesity in a population. To confront physical activity, efforts have examined zoning and access parks and safe routes in cities.{{Fact|date=August 2007}}
In the [[United Kingdom]], a 2004 report by the [[Royal College of Physicians]], the [[Faculty of Public Health]] and the [[Royal College of Paediatrics and Child Health]], titled "Storing up Problems",<ref>{{cite book |title=Storing up problems; the medical case for a slimmer nation |url=http://www.rcplondon.ac.uk/pubs/contents/ca4032bf-7b10-4e2f-8701-b24874f84514.pdf |format=PDF |date=2004-02-11 |publisher=Royal College of Physicians |location= London|isbn=1-86016-200-2}}</ref> was followed by a report by the [[British House of Commons]] [[Health Select Committee]] - the "the most comprehensive inquiry" ever by that body - on the impact of obesity on health and society in the UK and possible approaches to the problem.<ref>{{cite book |author=Great Britain Parliament House of Commons Health Committee |title=Obesity - Volume 1 - HCP 23-I, Third Report of session 2003-04. Report, together with formal minutes |url=http://www.publications.parliament.uk/pa/cm200304/cmselect/cmhealth/23/2302.htm |accessdate=2007-12-17|year=2004 |month= May|publisher=TSO (The Stationery Office) |location=London, UK |isbn=0-21501-737-4}}</ref> In 2006, the [[National Institute for Health and Clinical Excellence]] (NICE) issued a guideline on the diagnosis and management of obesity, as well as policy implications for non-healthcare organizations such as local councils.<ref name=NICECG043/> A 2007 report produced by Sir [[Derek Wanless]] for the [[King's Fund]] warned that unless further action was taken, obesity had the capacity to cripple the [[National Health Service]] financially.<ref>{{cite book |last=Wanless |first=Sir Derek |coauthors=John Appleby, Anthony Harrison, Darshan Patel |title=Our Future Health Secured? A review of NHS funding and performance |url=http://www.kingsfund.org.uk/publications/kings_fund_publications/our_future.html|accessdate=2007-12-17 |year=2007 |publisher=The King's Fund |location=London, UK |isbn=185717562X}}</ref>
===Non-medical consequences===
Besides increases in disease and mortality there are other implications of the present world trend in obesity. Among these are:
* Increased pressure on airline revenues (or increased fares) due to lobbying efforts to increase seating width on commercial airplanes, and due to higher fuel costs: in 2000, extra weight of obese passengers cost airlines and consumers US$275,000,000.<ref>{{cite journal |author=Dannenberg AL, Burton DC, Jackson RJ |title=Economic and environmental costs of obesity: the impact on airlines |journal=American journal of preventive medicine |volume=27 |issue=3 |pages=264 |year=2004 |pmid=15450642 |doi=10.1016/j.amepre.2004.06.004}}</ref>
* Increased litigation by obese persons suing restaurants (for causing obesity)<ref>109th U.S. Congress (2005-2006) H.R. 554: 109th U.S. Congress (2005-2006) H.R. 554: Personal Responsibility in Food Consumption Act of 2005</ref> and airlines (over airline seating width)[http://www.forbes.com/2002/10/24/cx_ld_1024obese.html] [http://www.cbc.ca/story/news/national/2000/12/12/Consumers/airlines_lawsuit001212.html]. The ''[[Personal Responsibility in Food Consumption Act]] of 2005'' was motivated by a need to reduce litigation from obesity activists.
* Sizable societal economic costs attributable to obesity, with medical costs attributable to obesity rising to 78.5 billion dollars or 9.1 percent of all medical expenditures in the U.S. as of 1998<ref>{{cite journal |author=Finkelstein EA, Fiebelkorn IA, Wang G |title=National medical spending attributable to overweight and obesity: how much, and who’s paying |journal=National medical spending attributable to overweight and obesity: how much, and who's paying |volume=Online |issue=May |pages=|year=2003 | url=http://content.healthaffairs.org/cgi/content/full/hlthaff.w3.219v1/DC1}}</ref><ref>{{cite web |url=http://www.cdc.gov/nccdphp/dnpa/obesity/economic_consequences.htm |title=Obesity and Overweight: Economic Consequences | publisher=CDC | pubdate=22 May 2007 | accessdate=2007-09-05}}</ref> One recent study, however, found that while obesity prevention programs reduce the cost of treating diseases related to obesity, those reductions are offset by medical costs during the additional years of life gained. The authors conclude that reducing obesity may improve public health, but is unlikely to reduce overall health spending.<ref>{{cite journal |author=van Baal PH, Polder JJ, de Wit GA, ''et al'' |title=Lifetime medical costs of obesity: prevention no cure for increasing health expenditure |journal=PLoS Med. |volume=5 |issue=2 |pages=e29 |year=2008 |month=February |pmid=18254654 |pmc=2225430 |doi=10.1371/journal.pmed.0050029 |url=http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050029}}</ref>
* Decreased worker productivity as measured by usage of disability leave and absenteeism at work.<ref>[http://www.dhs.ca.gov/ps/cdic/cpns/press/downloads/CostofObesityToplineReport.pdf The Economic Costs of Physical Inactivity, Obesity, and Overweight in California Adults], report by Chenoweth & Associates Inc. for the Cancer Prevention and Nutrition Section, California Center for Physical Activity, California Department of Health Services, Sacramento, CA, 2005.</ref>
* A study examining Duke University employees found that those with a BMI>40 filed twice as many workers compensation claims as workers whose BMI was 18.5-24.9, and had more than 12 times as many lost work days. The most common injuries were due to falls and lifting, and affected the lower extremities, wrists or hands, and backs.<ref>{{cite journal |author=Ostbye T, Dement JM, Krause KM |title=Obesity and workers' compensation: results from the Duke Health and Safety Surveillance System |journal=Arch. Intern. Med. |volume=167 |issue=8 |pages=766–73 |year=2007 |pmid=17452538 |doi=10.1001/archinte.167.8.766}}</ref>
==See also==
*[[Body image]]
*[[Chubby culture]]
*[[Feeder (fetish)|Feederism]]
*[[Healthy diet]]
*[[Human weight]]
*[[Junk food]]
*[[List of the most obese humans]]
*[[National Weight Control Registry]]
*[[Physical exercise]]
*[[Pickwickian syndrome]]
*[[Obesity in the United States]]
*[[Obesity in India]]
*[[Overeaters Anonymous]]
==References==
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==External links==
{{commonscat|Obesity}}
{{Wikinewscat|Obesity}}
{{Wiktionary}}
* [http://www.who.int/topics/obesity/en/ World Health Organization] - Obesity pages
* [http://www.who.int/nutrition/topics/dietnutrition_and_chronicdiseases/en/ Diet, Nutrition and the prevention of chronic diseases] (including obesity) by a Joint [[WHO]]/[[FAO]] Expert consultation (2003).
* [http://www.endotext.org/obesity/index.htm Obesity at Endotext.org]
* [http://www.iotf.org/ International Task Force on Obesity]
* [http://www.naaso.org The Obesity Society] (USA)
* [http://www.nationalobesityforum.org.uk/ National Obesity Forum] (UK)
* [http://www.asso.org.au Australasian Society for the Study of Obesity]
{{Nutritional pathology}}
[[Category:Obesity| ]]
[[Category:Metabolic disorders]]
[[Category:Health risks]]
[[Category:Nutrition]]
[[Category:Bariatrics]]
[[Category:Body shape]]
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