Obesity/ja

肥満
最適、過体重、肥満を表すシルエットとウエスト周囲径の値
Specialty	内分泌学
Symptoms	Increased fat
Complications	Cardiovascular disease/ja, type 2 diabetes/ja, obstructive sleep apnea/ja, ある種のcancer/ja, osteoarthritis/ja, うつ病
Causes	エネルギー密度の高い食品の過剰摂取、座りがちな仕事とライフスタイル、運動不足、交通手段の変化、都市化、支援政策の欠如、健康的な食事へのアクセス不足、遺伝
Diagnostic method	BMI > 30 kg/m2
Prevention	社会の変化、食品業界の変化、健康的なライフスタイルへのアクセス、個人の選択
Treatment	食事療法、運動療法、薬物療法、手術
Prognosis	平均寿命が短くなる
Frequency	10億人以上 / 12.5% (2022)
Deaths	年間2.8百万人

肥満とは、過剰な体脂肪が健康に悪影響を及ぼす可能性があるほど蓄積している医学的状態であり、時に病気とみなされる。体重を身長の2乗で割った体格指数（BMI）が30 kg/m²を超えると肥満と分類され、25–30 kg/m²の範囲が過体重と定義される。一部の東アジア諸国では、より低い値を用いて肥満を計算している。肥満は身体障害の主な原因であり、特に心血管系疾患、2型糖尿病、閉塞性睡眠時無呼吸症候群、ある種のがん、変形性関節症などさまざまな病気や状態と関連している。

肥満には個人的、社会経済的、環境的原因がある。知られている原因としては、食事、身体活動、自動化、都市化、遺伝的感受性、薬、精神障害、経済政策、内分泌障害、内分泌かく乱化学物質への暴露などがある。

常時、肥満者の大多数が減量を試み、成功することが多いが、減量を長期的に維持することはまれである。肥満を予防するための効果的で明確な、エビデンスに基づいた介入はない。肥満予防には、社会、地域社会、家族、個人レベルでの介入を含む複雑なアプローチが必要である。エクササイズと同様に食事の変更が、医療専門家によって推奨される主な治療法である。食事の質は、脂肪や糖分の多い食品などエネルギー密度の高い食品の摂取を減らし、食物繊維の摂取を増やすことで改善できる。薬物療法は、適切な食事療法とともに、食欲を減退させたり脂肪の吸収を減少させたりするために用いることができる。食事療法、運動療法、薬物療法が効果的でない場合は、胃バルーンや外科手術を行って胃の容積や腸の長さを減らし、早く満腹感を感じたり、食物からの栄養吸収能力を低下させたりすることがある。

肥満は世界的に予防可能な死因のトップであり、成人および小児の割合が増加している。2022年には、世界で10億人以上が肥満であり（成人8億7900万人、小児1億5900万人）、1990年に登録された成人の症例の2倍以上（小児の症例の4倍）であった。肥満は男性よりも女性に多い。今日、肥満は世界のほとんどの地域でスティグマである。逆に、過去も現在も、肥満を富と豊穣の象徴とみなして好意的にとらえている文化もある。世界保健機関、アメリカ、カナダ、日本、ポルトガル、ドイツ、欧州議会、医学会、例えばアメリカ医師会は肥満を病気として分類している。英国のように、そうでない国もある。

分類

詳細は「Classification of obesity/ja」を参照

カテゴリ	BMI (kg/m2)
アンダーウエイト	< 18.5
標準体重	18.5 – 24.9
オーバーウエイト	25.0 – 29.9
肥満 (クラス I)	30.0 – 34.9
肥満 (クラス II)	35.0 – 39.9
肥満 (クラス III)	≥ 40.0

BMI53 kg/m²の"超肥満"男性：体重182 kg (401 lb)、身長185 cm (6 ft 1 in)である。妊娠線と肥大した乳房を呈する。

肥満とは一般的に、健康に影響を及ぼす可能性のある体脂肪の実質的な蓄積として定義される。医療機関では、体格指数（BMI）、つまりキログラム単位の体重とメートル単位の身長の2乗の比率に基づいて、人々を肥満として分類する傾向がある。成人の場合、世界保健機関（WHO）はBMI 25以上を「過体重」、BMI 30以上を「肥満」と定義している。米国疾病管理予防センター（CDC）では、BMIをもとに肥満をさらに細分化しており、BMI30～35をクラス1肥満、35～40をクラス2肥満、40以上をクラス3肥満と呼んでいる。

子どもの場合、肥満の指標は身長と体重とともに年齢を考慮する。5～19歳の子どもについては、WHOはBMIが年齢の中央値を2標準偏差上回ることを肥満と定義している（5歳児のBMIは約18、19歳児は約30）。5歳未満の子どもの場合、WHOは身長の中央値より3標準偏差高い体重を肥満と定義している。

WHOの定義には、特定の団体によっていくつかの修正が加えられている。外科的な文献では、クラスⅡとⅢ、またはクラスⅢのみの肥満を、正確な値がまだ論争されているさらなるカテゴリーに分類している。

• BMIが35以上または40以上の場合は、高度肥満である。
• BMI≧35 kg/m²で、肥満に関連した健康状態を経験しているか、または≧40 kg/m²または≧45 kg/m²は病的肥満である。
• BMIが45以上または50 kg/m²以上は超肥満である。

アジア人集団は白人と比べてより低いBMI値で健康上の悪影響が現れるため、一部の国々では肥満の定義を見直しています。日本では肥満をBMI25kg/m²以上と定義し、中国ではBMI28kg/m²以上を肥満としている。

学者界で好まれている肥満の指標は体脂肪率（BF％）であり、体重に対する脂肪の総重量の割合である。女性は32％、男性は25％を超えると、一般的に肥満を示すと考えられている。

BMIは除脂肪体重、特に筋肉量の個人差を無視している。激しい肉体労働やスポーツに従事している人は、脂肪が少ないにもかかわらずBMI値が高いことがある。例えば、NFL選手の半数以上が「肥満」（BMI≧30）に分類され、BMIの指標によれば4人に1人が「極度の肥満」（BMI≧35）に分類される。しかし、彼らの平均体脂肪率は14％であり、健康的な範囲と考えられている。同様に、相撲力士はBMIでは「重度肥満」または「超重度肥満」に分類されるかもしれないが、代わりに体脂肪率を用いると多くの力士は肥満には分類されない（体脂肪率が25％未満である）。一部の力士は、非力士の比較群と比べて体脂肪がなく、除脂肪体重が多いためにBMI値が高いことが判明した。

健康への影響

肥満は、さまざまな代謝性疾患、心血管疾患、変形性関節症、アルツハイマー病、うつ病、およびある種のがんの発症リスクを高める。肥満の程度や併存疾患の有無にもよるが、肥満は推定2～20年の寿命短縮と関連している。高BMIは、食事や身体活動によって引き起こされる疾患のリスクの指標ではあるが、直接的な原因ではない。

死亡率

肥満は世界的に主要な予防可能な死因の一つである。死亡リスクは、非喫煙者ではBMI20～25kg/m²で最も低く、現在喫煙者ではBMI24～27kg/m²で最も低く、どちらかに変化するとリスクは増加する。これは少なくとも4大陸で当てはまるようである。他の研究によると、BMIおよびウエスト周囲径と死亡率との関連はU字型またはJ字型であるが、ウエスト-ヒップ比およびウエスト-身長比と死亡率との関連はよりポジティブである。アジア人では、健康への悪影響のリスクは22～25kg/m²の間で増加し始める。2021年、世界保健機関（WHO）は、肥満が毎年少なくとも280万人の死亡を引き起こすと推定した。平均して、肥満は平均余命を6～7年縮め、BMIが30～35 kg/m²では平均余命を2～4年縮め、重度の肥満（BMI ≥ 40 kg/m²）では平均余命を10年縮める。

罹患率

詳細は「肥満関連罹患率」を参照

Obesity increases the risk of many physical and mental conditions. These comorbidities are most commonly shown in metabolic syndrome, a combination of medical disorders which includes: diabetes mellitus type 2, high blood pressure, high blood cholesterol, and high triglyceride levels. A study from the RAK Hospital found that obese people are at a greater risk of developing long COVID. The CDC has found that obesity is the single strongest risk factor for severe COVID-19 illness.

Complications are either directly caused by obesity or indirectly related through mechanisms sharing a common cause such as a poor diet or a sedentary lifestyle. The strength of the link between obesity and specific conditions varies. One of the strongest is the link with type 2 diabetes. Excess body fat underlies 64% of cases of diabetes in men and 77% of cases in women.

Health consequences fall into two broad categories: those attributable to the effects of increased fat mass (such as osteoarthritis, obstructive sleep apnea, social stigmatization) and those due to the increased number of fat cells (diabetes, cancer, cardiovascular disease, non-alcoholic fatty liver disease). Increases in body fat alter the body's response to insulin, potentially leading to insulin resistance. Increased fat also creates a proinflammatory state, and a prothrombotic state.

Medical field	Condition	Medical field	Condition
Cardiology	Coronary heart disease: angina and myocardial infarction Congestive heart failure High blood pressure Abnormal cholesterol levels Deep vein thrombosis and pulmonary embolism	Dermatology	Acanthosis nigricans Lymphedema Cellulitis Hirsutism Intertrigo
Endocrinology and reproductive medicine	Diabetes mellitus Polycystic ovarian syndrome Menstrual disorders Infertility Complications during pregnancy Birth defects Intrauterine fetal death	Gastroenterology	Gastroesophageal reflux disease Fatty liver disease Cholelithiasis (gallstones)
Neurology	Stroke Meralgia paresthetica Migraines Carpal tunnel syndrome Dementia Idiopathic intracranial hypertension Multiple sclerosis	Oncology	Esophageal Colorectal Pancreatic Gallbladder Endometrial Kidney Leukemia Hepatocellular carcinoma Malignant melanoma
Psychiatry	Depression in women Social stigmatization	Respirology	Obstructive sleep apnea Obesity hypoventilation syndrome Asthma Increased complications during general anaesthesia increased risk of severe COVID-19
Rheumatology and orthopedics	Gout Poor mobility Osteoarthritis Low back pain	Urology and Nephrology	Erectile dysfunction Urinary incontinence Chronic renal failure Hypogonadism Buried penis

Metrics of health

Main article: Metabolically healthy obesity

Newer research has focused on methods of identifying healthier obese people by clinicians, and not treating obese people as a monolithic group. Obese people who do not experience medical complications from their obesity are sometimes called (metabolically) healthy obese, but the extent to which this group exists (especially among older people) is in dispute. The number of people considered metabolically healthy depends on the definition used, and there is no universally accepted definition. There are numerous obese people who have relatively few metabolic abnormalities, and a minority of obese people have no medical complications. The guidelines of the American Association of Clinical Endocrinologists call for physicians to use risk stratification with obese patients when considering how to assess their risk of developing type 2 diabetes.

In 2014, the BioSHaRE–EU Healthy Obese Project (sponsored by Maelstrom Research, a team under the Research Institute of the McGill University Health Centre) came up with two definitions for healthy obesity, one more strict and one less so:

BioSHaRE Healthy Obese (HOP) Project Criteria (2014)
A patient must have a body mass index ≥ 30, and all of the following:

	Less strict	More strict
Blood pressure measured as follows, with no pharmaceutical help
Overall (mmHg)	≤ 140	≤ 130
Systolic (mmHg)	N/A	≤ 85
Diastolic (mmHg)	≤ 90	N/A
Blood sugar level measured as follows, with no pharmaceutical help
Blood glucose (mmol/L)	≤ 7.0	≤ 6.1
Triglycerides measured as follows, with no pharmaceutical help
Fasting (mmol/L)	≤ 1.7
Non-fasting (mmol/L)	≤ 2.1
High-density lipoprotein measured as follows, with no pharmaceutical help
Men (mmol/L)	> 1.03
Women (mmol/L)	> 1.3
No diagnosis of any cardiovascular disease

To come up with these criteria, BioSHaRE controlled for age and tobacco use, researching how both may effect the metabolic syndrome associated with obesity, but not found to exist in the metabolically healthy obese. Other definitions of metabolically healthy obesity exist, including ones based on waist circumference rather than BMI, which is unreliable in certain individuals.

Another identification metric for health in obese people is calf strength, which is positively correlated with physical fitness in obese people. Body composition in general is hypothesized to help explain the existence of metabolically healthy obesity—the metabolically healthy obese are often found to have low amounts of ectopic fat (fat stored in tissues other than adipose tissue) despite having overall fat mass equivalent in weight to obese people with metabolic syndrome.

Survival paradox

See also: Obesity paradox

Although the negative health consequences of obesity in the general population are well supported by the available research evidence, health outcomes in certain subgroups seem to be improved at an increased BMI, a phenomenon known as the obesity survival paradox. The paradox was first described in 1999 in overweight and obese people undergoing hemodialysis and has subsequently been found in those with heart failure and peripheral artery disease (PAD).

In people with heart failure, those with a BMI between 30.0 and 34.9 had lower mortality than those with a normal weight. This has been attributed to the fact that people often lose weight as they become progressively more ill. Similar findings have been made in other types of heart disease. People with class I obesity and heart disease do not have greater rates of further heart problems than people of normal weight who also have heart disease. In people with greater degrees of obesity, however, the risk of further cardiovascular events is increased. Even after cardiac bypass surgery, no increase in mortality is seen in the overweight and obese. One study found that the improved survival could be explained by the more aggressive treatment obese people receive after a cardiac event. Another study found that if one takes into account chronic obstructive pulmonary disease (COPD) in those with PAD, the benefit of obesity no longer exists.

Causes

The "a calorie is a calorie" model of obesity posits a combination of excessive food energy intake and a lack of physical activity as the cause of most cases of obesity. A limited number of cases are due primarily to genetics, medical reasons, or psychiatric illness. In contrast, increasing rates of obesity at a societal level are felt to be due to an easily accessible and palatable diet, increased reliance on cars, and mechanized manufacturing.

Some other factors have been proposed as causes towards rising rates of obesity worldwide, including insufficient sleep, endocrine disruptors, increased usage of certain medications (such as atypical antipsychotics), increases in ambient temperature, decreased rates of smoking, demographic changes, increasing maternal age of first-time mothers, changes to epigenetic dysregulation from the environment, increased phenotypic variance via assortative mating, social pressure to diet, among others. According to one study, factors like these may play as big of a role as excessive food energy intake and a lack of physical activity; however, the relative magnitudes of the effects of any proposed cause of obesity is varied and uncertain, as there is a general need for randomized controlled trials on humans before definitive statement can be made.

According to the Endocrine Society, there is "growing evidence suggesting that obesity is a disorder of the energy homeostasis system, rather than simply arising from the passive accumulation of excess weight".

Diet

Main article: Diet and obesity

1961

2001–03

Map of dietary energy availability per person per day in 1961 (left) and 2001–2003 (right) Calories per person per day (kilojoules per person per day)

  No data

  <1,600 (<6,700)

  1,600–1,800 (6,700–7,500)

  1,800–2,000 (7,500–8,400)

  2,000–2,200 (8,400–9,200)

  2,200–2,400 (9,200–10,000)

  2,400–2,600 (10,000–10,900)

  2,600–2,800 (10,900–11,700)

  2,800–3,000 (11,700–12,600)

  3,000–3,200 (12,600–13,400)

  3,200–3,400 (13,400–14,200)

  3,400–3,600 (14,200–15,100)

  >3,600 (>15,100)

Average per capita energy consumption of the world from 1961 to 2002

Excess appetite for palatable, high-calorie food (especially fat, sugar, and certain animal proteins) is seen as the primary factor driving obesity worldwide, likely because of imbalances in neurotransmitters affecting the drive to eat. Dietary energy supply per capita varies markedly between different regions and countries. It has also changed significantly over time. From the early 1970s to the late 1990s the average food energy available per person per day (the amount of food bought) increased in all parts of the world except Eastern Europe. The United States had the highest availability with 3,654 calories (15,290 kJ) per person in 1996. This increased further in 2003 to 3,754 calories (15,710 kJ). During the late 1990s, Europeans had 3,394 calories (14,200 kJ) per person, in the developing areas of Asia there were 2,648 calories (11,080 kJ) per person, and in sub-Saharan Africa people had 2,176 calories (9,100 kJ) per person. Total food energy consumption has been found to be related to obesity.

Prevalence of obesity in the adult population by region (2000 - 2016)

The widespread availability of dietary guidelines has done little to address the problems of overeating and poor dietary choice. From 1971 to 2000, obesity rates in the United States increased from 14.5% to 30.9%. During the same period, an increase occurred in the average amount of food energy consumed. For women, the average increase was 335 calories (1,400 kJ) per day (1,542 calories (6,450 kJ) in 1971 and 1,877 calories (7,850 kJ) in 2004), while for men the average increase was 168 calories (700 kJ) per day (2,450 calories (10,300 kJ) in 1971 and 2,618 calories (10,950 kJ) in 2004). Most of this extra food energy came from an increase in carbohydrate consumption rather than fat consumption. The primary sources of these extra carbohydrates are sweetened beverages, which now account for almost 25 percent of daily food energy in young adults in America, and potato chips. Consumption of sweetened beverages such as soft drinks, fruit drinks, and iced tea is believed to be contributing to the rising rates of obesity and to an increased risk of metabolic syndrome and type 2 diabetes. Vitamin D deficiency is related to diseases associated with obesity.

As societies become increasingly reliant on energy-dense, big-portions, and fast-food meals, the association between fast-food consumption and obesity becomes more concerning. In the United States, consumption of fast-food meals tripled and food energy intake from these meals quadrupled between 1977 and 1995.

Agricultural policy and techniques in the United States and Europe have led to lower food prices. In the United States, subsidization of corn, soy, wheat, and rice through the U.S. farm bill has made the main sources of processed food cheap compared to fruits and vegetables. Calorie count laws and nutrition facts labels attempt to steer people toward making healthier food choices, including awareness of how much food energy is being consumed.

Obese people consistently under-report their food consumption as compared to people of normal weight. This is supported both by tests of people carried out in a calorimeter room and by direct observation.

Sedentary lifestyle

See also: Sedentary lifestyle and Exercise trends

A sedentary lifestyle may play a significant role in obesity. Worldwide there has been a large shift towards less physically demanding work, and currently at least 30% of the world's population gets insufficient exercise. This is primarily due to increasing use of mechanized transportation and a greater prevalence of labor-saving technology in the home. In children, there appear to be declines in levels of physical activity (with particularly strong declines in the amount of walking and physical education), likely due to safety concerns, changes in social interaction (such as fewer relationships with neighborhood children), and inadequate urban design (such as too few public spaces for safe physical activity). World trends in active leisure time physical activity are less clear. The World Health Organization indicates people worldwide are taking up less active recreational pursuits, while research from Finland found an increase and research from the United States found leisure-time physical activity has not changed significantly. Physical activity in children may not be a significant contributor.

In both children and adults, there is an association between television viewing time and the risk of obesity. Increased media exposure increases the rate of childhood obesity, with rates increasing proportionally to time spent watching television.

Genetics

Main article: Genetics of obesity

"La Monstrua Desnuda" (The Nude Monster), an 1680 painting by Juan Carreno de Miranda of a girl presumed to have Prader–Willi syndrome

Like many other medical conditions, obesity is the result of an interplay between genetic and environmental factors. Polymorphisms in various genes controlling appetite and metabolism predispose to obesity when sufficient food energy is present. As of 2006, more than 41 of these sites on the human genome have been linked to the development of obesity when a favorable environment is present. People with two copies of the FTO gene (fat mass and obesity associated gene) have been found on average to weigh 3–4 kg more and have a 1.67-fold greater risk of obesity compared with those without the risk allele. The differences in BMI between people that are due to genetics varies depending on the population examined from 6% to 85%.

Obesity is a major feature in several syndromes, such as Prader–Willi syndrome, Bardet–Biedl syndrome, Cohen syndrome, and MOMO syndrome. (The term "non-syndromic obesity" is sometimes used to exclude these conditions.) In people with early-onset severe obesity (defined by an onset before 10 years of age and body mass index over three standard deviations above normal), 7% harbor a single point DNA mutation.

Studies that have focused on inheritance patterns rather than on specific genes have found that 80% of the offspring of two obese parents were also obese, in contrast to less than 10% of the offspring of two parents who were of normal weight. Different people exposed to the same environment have different risks of obesity due to their underlying genetics.

The thrifty gene hypothesis postulates that, due to dietary scarcity during human evolution, people are prone to obesity. Their ability to take advantage of rare periods of abundance by storing energy as fat would be advantageous during times of varying food availability, and individuals with greater adipose reserves would be more likely to survive famine. This tendency to store fat, however, would be maladaptive in societies with stable food supplies. This theory has received various criticisms, and other evolutionarily-based theories such as the drifty gene hypothesis and the thrifty phenotype hypothesis have also been proposed.

Other illnesses

Certain physical and mental illnesses and the pharmaceutical substances used to treat them can increase risk of obesity. Medical illnesses that increase obesity risk include several rare genetic syndromes (listed above) as well as some congenital or acquired conditions: hypothyroidism, Cushing's syndrome, growth hormone deficiency, and some eating disorders such as binge eating disorder and night eating syndrome. However, obesity is not regarded as a psychiatric disorder, and therefore is not listed in the DSM-IVR as a psychiatric illness. The risk of overweight and obesity is higher in patients with psychiatric disorders than in persons without psychiatric disorders. Obesity and depression influence each other mutually, with obesity increasing the risk of clinical depression, and also depression leading to a higher chance of developing obesity.

Drug-induced obesity

Certain medications may cause weight gain or changes in body composition; these include insulin, sulfonylureas, thiazolidinediones, atypical antipsychotics, antidepressants, steroids, certain anticonvulsants (phenytoin and valproate), pizotifen, and some forms of hormonal contraception.

Social determinants

Main article: Social determinants of obesity

The disease scroll (Yamai no soshi, late 12th century) depicts a woman moneylender with obesity, considered a disease of the rich.

Obesity in developed countries is correlated with economic inequality.

While genetic influences are important to understanding obesity, they cannot completely explain the dramatic increase seen within specific countries or globally. Though it is accepted that energy consumption in excess of energy expenditure leads to increases in body weight on an individual basis, the cause of the shifts in these two factors on the societal scale is much debated. There are a number of theories as to the cause but most believe it is a combination of various factors.

The correlation between social class and BMI varies globally. Research in 1989 found that in developed countries women of a high social class were less likely to be obese. No significant differences were seen among men of different social classes. In the developing world, women, men, and children from high social classes had greater rates of obesity. In 2007 repeating the same research found the same relationships, but they were weaker. The decrease in strength of correlation was felt to be due to the effects of globalization. Among developed countries, levels of adult obesity, and percentage of teenage children who are overweight, are correlated with income inequality. A similar relationship is seen among US states: more adults, even in higher social classes, are obese in more unequal states.

Many explanations have been put forth for associations between BMI and social class. It is thought that in developed countries, the wealthy are able to afford more nutritious food, they are under greater social pressure to remain slim, and have more opportunities along with greater expectations for physical fitness. In undeveloped countries the ability to afford food, high energy expenditure with physical labor, and cultural values favoring a larger body size are believed to contribute to the observed patterns. Attitudes toward body weight held by people in one's life may also play a role in obesity. A correlation in BMI changes over time has been found among friends, siblings, and spouses. Stress and perceived low social status appear to increase risk of obesity.

Smoking has a significant effect on an individual's weight. Those who quit smoking gain an average of 4.4 kilograms (9.7 lb) for men and 5.0 kilograms (11.0 lb) for women over ten years. However, changing rates of smoking have had little effect on the overall rates of obesity.

In the United States, the number of children a person has is related to their risk of obesity. A woman's risk increases by 7% per child, while a man's risk increases by 4% per child. This could be partly explained by the fact that having dependent children decreases physical activity in Western parents.

In the developing world urbanization is playing a role in increasing rate of obesity. In China overall rates of obesity are below 5%; however, in some cities rates of obesity are greater than 20%. In part, this may be because of urban design issues (such as inadequate public spaces for physical activity). Time spent in motor vehicles, as opposed to active transportation options such as cycling or walking, is correlated with increased risk of obesity.

Malnutrition in early life is believed to play a role in the rising rates of obesity in the developing world. Endocrine changes that occur during periods of malnutrition may promote the storage of fat once more food energy becomes available.

Gut bacteria

See also: Infectobesity

The study of the effect of infectious agents on metabolism is still in its early stages. Gut flora has been shown to differ between lean and obese people. There is an indication that gut flora can affect the metabolic potential. This apparent alteration is believed to confer a greater capacity to harvest energy contributing to obesity. Whether these differences are the direct cause or the result of obesity has yet to be determined unequivocally. The use of antibiotics among children has also been associated with obesity later in life.

An association between viruses and obesity has been found in humans and several different animal species. The amount that these associations may have contributed to the rising rate of obesity is yet to be determined.

Other factors

Not getting enough sleep is also associated with obesity. Whether one causes the other is unclear. Even if short sleep does increase weight gain, it is unclear if this is to a meaningful degree or if increasing sleep would be of benefit.

Some have proposed that chemical compounds called "obesogens" may play a role in obesity.

Certain aspects of personality are associated with being obese. Loneliness, neuroticism, impulsivity, and sensitivity to reward are more common in people who are obese while conscientiousness and self-control are less common in people who are obese. Because most of the studies on this topic are questionnaire-based, it is possible that these findings overestimate the relationships between personality and obesity: people who are obese might be aware of the social stigma of obesity and their questionnaire responses might be biased accordingly. Similarly, the personalities of people who are obese as children might be influenced by obesity stigma, rather than these personality factors acting as risk factors for obesity.

In relation to globalization, it is known that trade liberalization is linked to obesity; research, based on data from 175 countries during 1975-2016, showed that obesity prevalence was positively correlated with trade openness, and the correlation was stronger in developing countries.

Pathophysiology

Main article: Pathophysiology of obesity

A comparison of a mouse unable to produce leptin thus resulting in obesity (left) and a normal mouse (right)

Two distinct but related processes are considered to be involved in the development of obesity: sustained positive energy balance (energy intake exceeding energy expenditure) and the resetting of the body weight "set point" at an increased value. The second process explains why finding effective obesity treatments has been difficult. While the underlying biology of this process still remains uncertain, research is beginning to clarify the mechanisms.

At a biological level, there are many possible pathophysiological mechanisms involved in the development and maintenance of obesity. This field of research had been almost unapproached until the leptin gene was discovered in 1994 by J. M. Friedman's laboratory. 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. 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.

The arcuate nucleus contains two distinct groups of neurons. 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.

Management

Main article: Management of obesity

The main treatment for obesity consists of weight loss via lifestyle interventions, including prescribed diets and physical exercise. Although it is unclear what diets might support long-term weight loss, and although the effectiveness of low-calorie diets is debated, lifestyle changes that reduce calorie consumption or increase physical exercise over the long term also tend to produce some sustained weight loss, despite slow weight regain over time. Although 87% of participants in the National Weight Control Registry were able to maintain 10% body weight loss for 10 years, the most appropriate dietary approach for long term weight loss maintenance is still unknown. In the US, intensive behavioral interventions combining both dietary changes and exercise are recommended. Intermittent fasting has no additional benefit of weight loss compared to continuous energy restriction. Adherence is a more important factor in weight loss success than whatever kind of diet an individual undertakes.

Several hypo-caloric diets are effective. In the short-term low carbohydrate diets appear better than low fat diets for weight loss. In the long term, however, all types of low-carbohydrate and low-fat diets appear equally beneficial. Heart disease and diabetes risks associated with different diets appear to be similar. Promotion of the Mediterranean diets among the obese may lower the risk of heart disease. Decreased intake of sweet drinks is also related to weight-loss. Success rates of long-term weight loss maintenance with lifestyle changes are low, ranging from 2–20%. Dietary and lifestyle changes are effective in limiting excessive weight gain in pregnancy and improve outcomes for both the mother and the child. Intensive behavioral counseling is recommended in those who are both obese and have other risk factors for heart disease.

Health policy

Prevalence of obesity in the adult population, top countries (2016)

Prevalence of obesity in the adult population in 2016

Obesity is a complex public health and policy problem because of its prevalence, costs, and health effects. As such, managing it requires changes in the wider societal context and effort by communities, local authorities, and governments. Public health efforts seek to understand and correct the environmental factors responsible for the increasing prevalence of obesity in the population. Solutions look at changing the factors that cause excess food energy consumption and inhibit physical activity. Efforts include federally reimbursed meal programs in schools, limiting direct junk food marketing to children, and decreasing access to sugar-sweetened beverages in schools. The World Health Organization recommends the taxing of sugary drinks. When constructing urban environments, efforts have been made to increase access to parks and to develop pedestrian routes.

Mass media campaigns seem to have limited effectiveness in changing behaviors that influence obesity, but may increase knowledge and awareness regarding physical activity and diet, which might lead to changes in the long term. Campaigns might also be able to reduce the amount of time spent sitting or lying down and positively affect the intention to be active physically. Nutritional labelling with energy information on menus might be able to help reducing energy intake while dining in restaurants. Some call for policy against ultra-processed foods.

Medical interventions

Medication

Main article: Anti-obesity medication

Since the introduction of medicines for the management of obesity in the 1930s, many compounds have been tried. Most of them reduce body weight by small amounts, and several of them are no longer marketed for obesity because of their side effects. Out of 25 anti-obesity medications withdrawn from the market between 1964 and 2009, 23 acted by altering the functions of chemical neurotransmitters in the brain. The most common side effects of these drugs that led to withdrawals were mental disturbances, cardiac side effects, and drug abuse or drug dependence. Deaths were reportedly associated with seven products.

Five medications beneficial for long-term use are: orlistat, lorcaserin, liraglutide, phentermine–topiramate, and naltrexone–bupropion. They result in weight loss after one year ranged from 3.0 to 6.7 kg (6.6-14.8 lbs) over placebo. Orlistat, liraglutide, and naltrexone–bupropion are available in both the United States and Europe, phentermine–topiramate is available only in the United States. European regulatory authorities rejected lorcaserin and phentermine-topiramate, in part because of associations of heart valve problems with lorcaserin and more general heart and blood vessel problems with phentermine–topiramate. Lorcaserin was available in the United States and then removed from the market in 2020 due to its association with cancer. Orlistat use is associated with high rates of gastrointestinal side effects and concerns have been raised about negative effects on the kidneys. There is no information on how these drugs affect longer-term complications of obesity such as cardiovascular disease or death; however, liraglutide, when used for type 2 diabetes, does reduce cardiovascular events.

In 2019 a systematic review compared the effects on weight of various doses of fluoxetine (60 mg/d, 40 mg/d, 20 mg/d, 10 mg/d) in obese adults. When compared to placebo, all dosages of fluoxetine appeared to contribute to weight loss but lead to increased risk of experiencing side effects such as dizziness, drowsiness, fatigue, insomnia and nausea during period of treatment. However, these conclusions were from low certainty evidence. When comparing, in the same review, the effects of fluoxetine on weight of obese adults, to other anti-obesity agents, omega-3 gel and not receiving a treatment, the authors could not reach conclusive results due to poor quality of evidence.

Among antipsychotic drugs for treating schizophrenia clozapine is the most effective, but it also has the highest risk of causing the metabolic syndrome, of which obesity is the main feature. For people who gain weight because of clozapine, taking metformin may reportedly improve three of the five components of the metabolic syndrome: waist circumference, fasting glucose, and fasting triglycerides.

Surgery

The most effective treatment for obesity is bariatric surgery. The types of procedures include laparoscopic adjustable gastric banding, Roux-en-Y gastric bypass, vertical-sleeve gastrectomy, and biliopancreatic diversion. Surgery for severe obesity is associated with long-term weight loss, improvement in obesity-related conditions, and decreased overall mortality; however, improved metabolic health results from the weight loss, not the surgery. One study found a weight loss of between 14% and 25% (depending on the type of procedure performed) at 10 years, and a 29% reduction in all cause mortality when compared to standard weight loss measures. Complications occur in about 17% of cases and reoperation is needed in 7% of cases.

Epidemiology

Main article: Epidemiology of obesity

Share of adults with BMIs > 30 (2016)

See or edit source data.

In earlier historical periods obesity was rare and achievable only by a small elite, although already recognised as a problem for health. But as prosperity increased in the Early Modern period, it affected increasingly larger groups of the population. Prior to the 1970s, obesity was a relatively rare condition even in the wealthiest of nations, and when it did exist it tended to occur among the wealthy. Then, a confluence of events started to change the human condition. The average BMI of populations in first-world countries started to increase, and consequently there was a rapid increase in the proportion of people overweight and obese.

In 1997, the WHO formally recognized obesity as a global epidemic. As of 2008, the WHO estimates that at least 500 million adults (greater than 10%) are obese, with higher rates among women than men. The global prevalence of obesity more than doubled between 1980 and 2014. In 2014, more than 600 million adults were obese, equal to about 13 percent of the world's adult population. The percentage of adults affected in the United States as of 2015–2016 is about 39.6% overall (37.9% of males and 41.1% of females). In 2000, the World Health Organization (WHO) stated that overweight and obesity were replacing more traditional public health concerns such as undernutrition and infectious diseases as one of the most significant cause of poor health.

The rate of obesity also increases with age at least up to 50 or 60 years old and severe obesity in the United States, Australia, and Canada is increasing faster than the overall rate of obesity. The OECD has projected an increase in obesity rates until at least 2030, especially in the United States, Mexico and England with rates reaching 47%, 39% and 35%, respectively.

Once considered a problem only of high-income countries, obesity rates are rising worldwide and affecting both the developed and developing world. These increases have been felt most dramatically in urban settings.

Sex- and gender-based differences also influence the prevalence of obesity. Globally there are more obese women than men, but the numbers differ depending on how obesity is measured.

History

Etymology

Obesity is from the Latin obesitas, which means "stout, fat, or plump". Ēsus is the past participle of edere (to eat), with ob (over) added to it. The Oxford English Dictionary documents its first usage in 1611 by Randle Cotgrave.

Historical attitudes

During the Middle Ages and the Renaissance The Tuscan General Alessandro del Borro, attributed to Charles Mellin, 1645

Venus of Willendorf created 24,000–22,000 BC

Ancient Greek medicine recognizes obesity as a medical disorder and records that the Ancient Egyptians saw it in the same way. Hippocrates wrote that "Corpulence is not only a disease itself, but the harbinger of others". The Indian surgeon Sushruta (6th century BCE) related obesity to diabetes and heart disorders. He recommended physical work to help cure it and its side effects. For most of human history, mankind struggled with food scarcity. Obesity has thus historically been viewed as a sign of wealth and prosperity. It was common among high officials in Ancient East Asian civilizations. In the 17th century, English medical author Tobias Venner is credited with being one of the first to refer to the term as a societal disease in a published English language book.

With the onset of the Industrial Revolution, it was realized that the military and economic might of nations were dependent on both the body size and strength of their soldiers and workers. Increasing the average body mass index from what is now considered underweight to what is now the normal range played a significant role in the development of industrialized societies. Height and weight thus both increased through the 19th century in the developed world. During the 20th century, as populations reached their genetic potential for height, weight began increasing much more than height, resulting in obesity. In the 1950s, increasing wealth in the developed world decreased child mortality, but as body weight increased, heart and kidney disease became more common. During this time period, insurance companies realized the connection between weight and life expectancy and increased premiums for the obese.

Many cultures throughout history have viewed obesity as the result of a character flaw. The obesus or fat character in Ancient Greek comedy was a glutton and figure of mockery. During Christian times, food was viewed as a gateway to the sins of sloth and lust. In modern Western culture, excess weight is often regarded as unattractive, and obesity is commonly associated with various negative stereotypes. People of all ages can face social stigmatization and may be targeted by bullies or shunned by their peers.

Public perceptions in Western society regarding healthy body weight differ from those regarding the weight that is considered ideal – and both have changed since the beginning of the 20th century. The weight that is viewed as an ideal has become lower since the 1920s. This is illustrated by the fact that the average height of Miss America pageant winners increased by 2% from 1922 to 1999, while their average weight decreased by 12%. On the other hand, people's views concerning healthy weight have changed in the opposite direction. In Britain, the weight at which people considered themselves to be overweight was significantly higher in 2007 than in 1999. These changes are believed to be due to increasing rates of adiposity leading to increased acceptance of extra body fat as being normal.

Obesity is still seen as a sign of wealth and well-being in many parts of Africa. This has become particularly common since the HIV epidemic began.

The arts

The first sculptural representations of the human body 20,000–35,000 years ago depict obese females. Some attribute the Venus figurines to the tendency to emphasize fertility while others feel they represent "fatness" in the people of the time. Corpulence is, however, absent in both Greek and Roman art, probably in keeping with their ideals regarding moderation. This continued through much of Christian European history, with only those of low socioeconomic status being depicted as obese.

During the Renaissance some of the upper class began flaunting their large size, as can be seen in portraits of Henry VIII of England and Alessandro dal Borro. Rubens (1577–1640) regularly depicted heavyset women in his pictures, from which derives the term Rubenesque. These women, however, still maintained the "hourglass" shape with its relationship to fertility. During the 19th century, views on obesity changed in the Western world. After centuries of obesity being synonymous with wealth and social status, slimness began to be seen as the desirable standard. In his 1819 print, The Belle Alliance, or the Female Reformers of Blackburn!!!, artist George Cruikshank criticised the work of female reformers in Blackburn and used fatness as a means to portray them as unfeminine.

Society and culture

Economic impact

In addition to its health impacts, obesity leads to many problems, including disadvantages in employment and increased business costs. These effects are felt by all levels of society, from individuals, to corporations, to governments.

In 2005, the medical costs attributable to obesity in the US were an estimated $190.2 billion or 20.6% of all medical expenditures, while the cost of obesity in Canada was estimated at CA$2 billion in 1997 (2.4% of total health costs). The total annual direct cost of overweight and obesity in Australia in 2005 was A$21 billion. Overweight and obese Australians also received A$35.6 billion in government subsidies. The estimated range for annual expenditures on diet products is $40 billion to $100 billion in the US alone.

The Lancet Commission on Obesity in 2019 called for a global treaty—modelled on the WHO Framework Convention on Tobacco Control—committing countries to address obesity and undernutrition, explicitly excluding the food industry from policy development. They estimate the global cost of obesity $2 trillion a year, about or 2.8% of world GDP.

Obesity prevention programs have been found to reduce the cost of treating obesity-related disease. However, the longer people live, the more medical costs they incur. Researchers, therefore, conclude that reducing obesity may improve the public's health, but it is unlikely to reduce overall health spending. Sin taxes such as a sugary drink tax have been implemented in certain countries globally to curb dietary and consumer habits, and as an effort to offset the economic tolls.

Services accommodate obese people with specialized equipment such as much wider chairs.

Obesity can lead to social stigmatization and disadvantages in employment. When compared to their normal weight counterparts, obese workers on average have higher rates of absenteeism from work and take more disability leave, thus increasing costs for employers and decreasing productivity. A study examining Duke University employees found that people with a BMI over 40 kg/m² filed twice as many workers' compensation claims as those whose BMI was 18.5–24.9 kg/m². They also had more than 12 times as many lost work days. The most common injuries in this group were due to falls and lifting, thus affecting the lower extremities, wrists or hands, and backs. The Alabama State Employees' Insurance Board approved a controversial plan to charge obese workers $25 a month for health insurance that would otherwise be free unless they take steps to lose weight and improve their health. These measures started in January 2010 and apply to those state workers whose BMI exceeds 35 kg/m² and who fail to make improvements in their health after one year.

Some research shows that obese people are less likely to be hired for a job and are less likely to be promoted. Obese people are also paid less than their non-obese counterparts for an equivalent job; obese women on average make 6% less and obese men make 3% less.

Specific industries, such as the airline, healthcare and food industries, have special concerns. Due to rising rates of obesity, airlines face higher fuel costs and pressures to increase seating width. In 2000, the extra weight of obese passengers cost airlines US$275 million. The healthcare industry has had to invest in special facilities for handling severely obese patients, including special lifting equipment and bariatric ambulances. Costs for restaurants are increased by litigation accusing them of causing obesity. In 2005, the US Congress discussed legislation to prevent civil lawsuits against the food industry in relation to obesity; however, it did not become law.

With the American Medical Association's 2013 classification of obesity as a chronic disease, it is thought that health insurance companies will more likely pay for obesity treatment, counseling and surgery, and the cost of research and development of fat treatment pills or gene therapy treatments should be more affordable if insurers help to subsidize their cost. The AMA classification is not legally binding, however, so health insurers still have the right to reject coverage for a treatment or procedure.

In 2014, The European Court of Justice ruled that morbid obesity is a disability. The Court said that if an employee's obesity prevents them from "full and effective participation of that person in professional life on an equal basis with other workers", then it shall be considered a disability and that firing someone on such grounds is discriminatory.

In low-income countries, obesity can be a signal of wealth. A 2023 experimental study found that obese individuals in Uganda were more likely to access credit.

Size acceptance

See also: Fat acceptance movement, Social stigma of obesity, Health at Every Size, and Fat fetishism

United States President William Howard Taft was often ridiculed for being overweight.

German politician Ricarda Lang is a victim of fat shaming on the internet.

The principal goal of the fat acceptance movement is to decrease discrimination against people who are overweight and obese. However, some in the movement are also attempting to challenge the established relationship between obesity and negative health outcomes.

A number of organizations exist that promote the acceptance of obesity. They have increased in prominence in the latter half of the 20th century. The US-based National Association to Advance Fat Acceptance (NAAFA) was formed in 1969 and describes itself as a civil rights organization dedicated to ending size discrimination.

The International Size Acceptance Association (ISAA) is a non-governmental organization (NGO) which was founded in 1997. It has more of a global orientation and describes its mission as promoting size acceptance and helping to end weight-based discrimination. These groups often argue for the recognition of obesity as a disability under the US Americans With Disabilities Act (ADA). The American legal system, however, has decided that the potential public health costs exceed the benefits of extending this anti-discrimination law to cover obesity.

Industry influence on research

In 2015, the New York Times published an article on the Global Energy Balance Network, a nonprofit founded in 2014 that advocated for people to focus on increasing exercise rather than reducing calorie intake to avoid obesity and to be healthy. The organization was founded with at least $1.5M in funding from the Coca-Cola Company, and the company has provided $4M in research funding to the two founding scientists Gregory A. Hand and Steven N. Blair since 2008.

報告書

多くの団体が肥満に関する報告書を発表している。1998年、「成人の過体重および肥満の同定、評価、治療に関する臨床ガイドライン」と題する米国初の連邦ガイドラインが発表された： "The Evidence Report"と題された。2006年、カナダ肥満ネットワーク（現在は肥満カナダとして知られる）は、"成人および小児の肥満の管理と予防に関するカナダの臨床実践ガイドライン（CPG）"を発表した。これは、成人および小児の過体重と肥満の管理と予防に対処するための包括的なエビデンスに基づくガイドラインである。

In 2004, the United Kingdom Royal College of Physicians, the Faculty of Public Health and the Royal College of Paediatrics and Child Health released the report "Storing up Problems", which highlighted the growing problem of obesity in the UK. The same year, the House of Commons Health Select Committee published its "most comprehensive inquiry [...] ever undertaken" into the impact of obesity on health and society in the UK and possible approaches to the problem. 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. A 2007 report produced by Derek Wanless for the King's Fund warned that unless further action was taken, obesity had the capacity to debilitate the National Health Service financially. In 2022 the National Institute for Health and Care Research (NIHR) published a comprehensive review of research on what local authorities can do to reduce obesity.

The Obesity Policy Action (OPA) framework divides measure into upstream policies, midstream policies, and downstream policies. Upstream policies have to do with changing society, while midstream policies try to alter behaviors believed to contribute to obesity at the individual level, while downstream policies treat currently obese people.

小児肥満

詳細は「Childhood obesity/ja」を参照

健康なBMIの範囲は、子供の年齢と性別によって異なる。小児および青年の肥満は、BMIが95パーセンタイルパーセンタイル以上と定義される。これらのパーセンタイルが基づく基準データは1963年から1994年までのものであるため、最近の肥満率の増加の影響は受けていない。小児肥満は21世紀に入って流行の兆しを見せており、先進国でも発展途上国でも肥満率が上昇している。カナダの男児の肥満率は、1980年代の11％から1990年代には30％以上に増加し、同じ期間にブラジルの子供たちの肥満率は4％から14％に増加した。イギリスでは、1989年と比較して2005年には60％も肥満の子供が増えている。アメリカでは、太りすぎと肥満の子供の割合は2008年には16％に増加し、それ以前の30年間で300％増加した。

成人の肥満と同様、小児肥満の増加にも多くの要因がある。食生活の変化と運動量の減少が、最近の子どもの肥満率増加の2大原因と考えられている。また、子どもへの不健康な食品の広告も、子どもの消費量を増加させるため、寄与している。生後6ヵ月間の抗生物質は、7～12歳時の体重超過と関連している。小児期の肥満はしばしば成人期まで持続し、多くの慢性疾患と関連するため、肥満の子どもはしばしば高血圧、糖尿病、高脂血症、脂肪肝疾患の検査を受ける。

小児に使用される治療法は、主に生活習慣への介入と行動テクニックであるが、小児の活動性を高める努力はほとんど成功していない。米国では、この年齢層に使用する薬剤はFDAに承認されていない。プライマリケアにおける短時間の体重管理介入（例えば、医師またはナースプラクティショナーによる）は、小児の過体重または肥満の減少においてわずかなプラスの効果しかない。食事と身体活動の変更を含む多成分の行動変容介入は、6～11歳の小児において短期的にBMIを低下させる可能性があるが、有益性は小さく、エビデンスの質も低い。

その他の動物

詳細は「Obesity in pets/ja」を参照

ペットの肥満は多くの国で見られる。アメリカでは、犬の23～41％が太りすぎで、約5.1％が肥満である。猫の肥満率は6.4％とやや高い。オーストラリアでは、獣医学的環境における犬の肥満率は7.6％であることが判明している。犬の肥満リスクは飼い主が肥満であるかどうかに関係しているが、猫と飼い主の間には同様の相関関係はない。

こちらも参照

• Portal-visceral hypothesis/ja
• Anti-Obesity Day/ja

さらに読む

Wikipedia's health care articles can be viewed offline with the Medical Wikipedia app.

• "Obesity 2015". The Lancet. 2015. Series from the Lancet journals
• Jebb S, Wells J (2005). "Measuring body composition in adults and children". In Kopelman PG, Caterson ID, Stock MJ, Dietz WH (eds.). Clinical obesity in adults and children: In Adults and Children. Blackwell Publishing. pp. 12–28. ISBN 978-1-4051-1672-5.
• National Heart, Lung, and Blood Institute (NHLBI) (1998). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults (PDF). International Medical Publishing, Inc. ISBN 978-1-58808-002-8.
• "Obesity: guidance on the prevention, identification, assessment and management of overweight and obesity in adults and children" (PDF). National Institute for Health and Clinical Excellence(NICE). National Health Services (NHS). 2006. Retrieved 8 April 2009.
• World Health Organization (WHO) (2000). Technical report series 894: Obesity: Preventing and managing the global epidemic (PDF). Geneva: World Health Organization. ISBN 978-92-4-120894-9. Archived from the original (PDF) on 1 May 2015. Retrieved 10 May 2006.

外部リンク

• Quotations related to Obesity at Wikiquote
• WHO fact sheet on obesity and overweight