Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health, leading to reduced life expectancy and/or increased health problems.[1][2] In Western countries, people are considered obese when their body mass index (BMI),[3] a measurement obtained by dividing a person’s weight by the square of the person’s height, exceeds 30 kg/m2, with the range 25-30 kg/m2 defined as overweight. Some East Asiancountries use stricter criteria.

Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, obstructive sleep apnea, certain types of cancer, and osteoarthritis.[2] Obesity is most commonly caused by a combination of excessive food energyintake, lack of physical activity, and genetic susceptibility, although a few cases are caused primarily by genes, endocrinedisorders, medications, or psychiatric illness. Evidence to support the view that some obese people eat little yet gain weight due to a slow metabolism is limited. On average, obese people have a greater energy expenditure than their thin counterparts due to the energy required to maintain an increased body mass.[4][5]

Dieting and exercising are the main treatments for obesity. Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat and sugars, and by increasing the intake of dietary fiber. With a suitable diet,anti-obesity drugs may be taken to reduce appetite or decrease fat absorption. If diet, exercise, and medication are not effective, a gastric balloon may assist with weight loss, or surgery may be performed to reduce stomach volume and/or bowel length, leading to feeling full earlier and a reduced ability to absorb nutrients from food.[6][7]

Obesity is a leading preventable cause of death worldwide, with increasing rates in adults and children. Authorities view it as one of the most serious public health problems of the 21st century.[8] Obesity is stigmatized in much of the modern world (particularly in the Western world), though it was widely seen as a symbol of wealth and fertility at other times in history and still is in some parts of the world.[2][9] In 2013, the American Medical Associationclassified obesity as a disease.


At an individual level, a combination of excessive food energy intake and a lack of physical activity is thought to explain most cases of obesity.[68] A limited number of cases are due primarily to genetics, medical reasons, or psychiatric illness.[69] In contrast, increasing rates of obesity at a societal level are felt to be due to an easily accessible and palatable diet,[70] increased reliance on cars, and mechanized manufacturing.[71][72]

A 2006 review identified ten other possible contributors to the recent increase of obesity: (1) insufficient sleep, (2) endocrine disruptors (environmental pollutants that interfere with lipid metabolism), (3) decreased variability in ambient temperature, (4) decreased rates of smoking, because smoking suppresses appetite, (5) increased use of medications that can cause weight gain (e.g., atypical antipsychotics), (6) proportional increases in ethnic and age groups that tend to be heavier, (7) pregnancy at a later age (which may cause susceptibility to obesity in children), (8) epigenetic risk factors passed on generationally, (9) natural selection for higher BMI, and (10)assortative mating leading to increased concentration of obesity risk factors (this would increase the number of obese people by increasing population variance in weight).[73] While there is substantial evidence supporting the influence of these mechanisms on the increased prevalence of obesity, the evidence is still inconclusive, and the authors state that these are probably less influential than the ones discussed in the previous paragraph.

Historical attitudes

A very obese gentleman with a prominent double chin and mustache dressed in black with a sword at his left side.

During the Middle Ages and theRenaissanceobesity was often seen as a sign of wealth, and was relatively common among the elite:The Tuscan General Alessandro del Borro, attributed to Charles Mellin, 1645[176]

A carved stone miniature figurine depicted an obese female.

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.[169]Hippocrates wrote that “Corpulence is not only a disease itself, but the harbinger of others”.[2] The Indian surgeon Sushruta (6th century BCE) related obesity to diabetes and heart disorders.[177] He recommended physical work to help cure it and its side effects.[177] For most of human history mankind struggled with food scarcity.[178] Obesity has thus historically been viewed as a sign of wealth and prosperity. It was common among high officials in Europe in the Middle Ages and the Renaissance[176] as well as in Ancient East Asian civilizations.[179]

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.[81] 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.[81] 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.[81] In the 1950s increasing wealth in the developed world decreased child mortality, but as body weight increased heart and kidney disease became more common.[81][180] During this time period insurance companies realized the connection between weight and life expectancy and increased premiums for the obese.[2]

Many cultures throughout history have viewed obesity as the result of a character flaw. The obesus or fat character in 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.[9] 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. Obesity is once again a reason for discrimination.[181]

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%.[182] 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.[183] These changes are believed to be due to increasing rates of adiposity leading to increased acceptance of extra body fat as being normal.[183]

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.[2]

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.[9] 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.[9]

During the Renaissance some of the upper class began flaunting their large size, as can be seen in portraits of Henry VIII of England andAlessandro del Borro.[9] Rubens (1577–1640) regularly depicted full-bodied women in his pictures, from which derives the term Rubenesque. These women, however, still maintained the “hourglass” shape with its relationship to fertility.[184] 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.[9]

Society and culture

Economic impact

In addition to its health impacts, obesity leads to many problems including disadvantages in employment[185][186] 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,[187][188][189] while the cost of obesity in Canada was estimated at CA$2 billion in 1997 (2.4% of total health costs).[68] 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.[190] The estimate range for annual expenditures on diet products is $40 billion to $100 billion in the US alone.[191]

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.[192]

An extra wide chair beside a number of normal sized chairs.

Services must accommodate obese people with specialist equipment such as much wider chairs.[193]

Obesity can lead to social stigmatization and disadvantages in employment.[185] 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.[194] A study examining Duke University employees found that people with a BMI over 40 kg/m2 filed twice as manyworkers’ 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.[195] 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.[196]

Some research shows that obese people are less likely to be hired for a job and are less likely to be promoted.[181] 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.[197]

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.[198] In 2000, the extra weight of obese passengers cost airlines US$275 million.[199] The healthcare industry has had to invest in special facilities for handling severely obese patients, including special lifting equipment and bariatric ambulances.[200] Costs for restaurants are increased by litigation accusing them of causing obesity.[201] 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.[201]

With the American Medical Association‘s 2013 classification of obesity as chronic disease,[10] 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.[202] The AMA classification is not legally binding, however, so health insurers still have the right to reject coverage for a treatment or procedure.[202]

Size acceptance

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

The principal goal of the fat acceptance movement is to decrease discrimination against people who are overweight and obese.[203][204] However, some in the movement are also attempting to challenge the established relationship between obesity and negative health outcomes.[205]

A number of organizations exist that promote the acceptance of obesity. They have increased in prominence in the latter half of the 20th century.[206] 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.[207]

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.[208] 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.[205]

Childhood obesity

Main article: Childhood obesity

The healthy BMI range varies with the age and sex of the child. Obesity in children and adolescents is defined as a BMI greater than the 95th percentile.[15] The reference data that these percentiles are based on is from 1963 to 1994 and thus has not been affected by the recent increases in rates of obesity.[16] Childhood obesity has reached epidemic proportions in 21st century, with rising rates in both the developed and developing world. Rates of obesity in Canadian boys have increased from 11% in 1980s to over 30% in 1990s, while during this same time period rates increased from 4 to 14% in Brazilian children.[209]

As with obesity in adults, many different factors contribute to the rising rates of childhood obesity. Changing diet and decreasing physical activity are believed to be the two most important in causing the recent increase in the rates.[210] Because childhood obesity often persists into adulthood and is associated with numerous chronic illnesses, children who are obese are often tested for hypertension, diabetes, hyperlipidemia, and fatty liver.[68] Treatments used in children are primarily lifestyle interventions and behavioral techniques, although efforts to increase activity in children have had little success.[211] In the United States, medications are not FDA approved for use in this age group.[209]


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