Obesity

Obesity
Three silhouettes depicting the outlines of an optimally sized (left), overweight (middle), and obese person (right).
Silhouettes and waist circumferences representing optimal, overweight, and obese
SpecialtyEndocrinology
SymptomsIncreased fat[1]
ComplicationsCardiovascular diseases, type 2 diabetes, obstructive sleep apnea, certain types of cancer, osteoarthritis, depression[2][3]
CausesExcessive food, lack of exercise, genetics[1][4]
Diagnostic methodBMI > 30 kg/m2[1]
PreventionSocietal changes, personal choices[1]
TreatmentDiet, exercise, medications, surgery[1][5][6]
PrognosisReduced life expectancy[2]
Frequency700 million / 12% (2015)[7]

Obesity is a medical condition in which excess body fat has accumulated to an extent that it may have a negative effect on health.[1] People are generally considered obese when their body mass index (BMI), a measurement obtained by dividing a person's weight by the square of the person's height, is over 30 kg/m2; the range 25–30 kg/m2 is defined as overweight.[1] Some East Asian countries use lower values.[8] Obesity increases the likelihood of various diseases and conditions, particularly cardiovascular diseases, type 2 diabetes, obstructive sleep apnea, certain types of cancer, osteoarthritis, and depression.[2][3]

Obesity is most commonly caused by a combination of excessive food intake, lack of physical activity, and genetic susceptibility.[1][4] A few cases are caused primarily by genes, endocrine disorders, medications, or mental disorder.[9] The view that obese people eat little yet gain weight due to a slow metabolism is not medically supported.[10] On average, obese people have a greater energy expenditure than their normal counterparts due to the energy required to maintain an increased body mass.[10][11]

Obesity is mostly preventable through a combination of social changes and personal choices.[1] Changes to diet and exercising are the main treatments.[2] Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat or sugars, and by increasing the intake of dietary fiber.[1] Medications can be used, along with a suitable diet, to reduce appetite or decrease fat absorption.[5] If diet, exercise, and medication are not effective, a gastric balloon or surgery may be performed to reduce stomach volume or length of the intestines, leading to feeling full earlier or a reduced ability to absorb nutrients from food.[6][12]

Obesity is a leading preventable cause of death worldwide, with increasing rates in adults and children.[1][13] In 2015, 600 million adults (12%) and 100 million children were obese in 195 countries.[7] Obesity is more common in women than men.[1] Authorities view it as one of the most serious public health problems of the 21st century.[14] Obesity is stigmatized in much of the modern world (particularly in the Western world), though it was seen as a symbol of wealth and fertility at other times in history and still is in some parts of the world.[2][15] In 2013, several medical societies, including the American Medical Association and the American Heart Association, classified obesity as a disease.[16][17][18]

Classification

BMI (kg/m2) Classification[19]
from up to
18.5 underweight
18.5 25.0 normal weight
25.0 30.0 overweight
30.0 35.0 class I obesity
35.0 40.0 class II obesity
40.0 class III obesity  
A front and side view of a "super obese" male torso. Stretch marks of the skin are visible along with gynecomastia.
A "super obese" male with a BMI of 53 kg/m2: weight 182 kg (400 lb), height 185 cm (6 ft 1 in). He presents with stretch marks and enlarged breasts

Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health.[20] It is defined by body mass index (BMI) and further evaluated in terms of fat distribution via the waist–hip ratio and total cardiovascular risk factors.[21][22] BMI is closely related to both percentage body fat and total body fat.[23] In children, a healthy weight varies with age and sex. Obesity in children and adolescents is defined not as an absolute number but in relation to a historical normal group, such that obesity is a BMI greater than the 95th percentile.[24] The reference data on which these percentiles were based date from 1963 to 1994, and thus have not been affected by the recent increases in weight.[25] BMI is defined as the subject's weight divided by the square of their height and is calculated as follows.

,
where m and h are the subject's weight and height respectively.

BMI is usually expressed in kilograms of weight per metre squared of height. To convert from pounds per inch squared multiply by 703 (kg/m2)/(lb/sq in).[26]

The most commonly used definitions, established by the World Health Organization (WHO) in 1997 and published in 2000, provide the values listed in the table.[27][28]

Some modifications to the WHO definitions have been made by particular organizations.[29] The surgical literature breaks down class II and III obesity into further categories whose exact values are still disputed.[30]

  • Any BMI ≥ 35 or 40 kg/m2 is severe obesity.
  • A BMI of ≥ 35 kg/m2 and experiencing obesity-related health conditions or ≥40–44.9 kg/m2 is morbid obesity.
  • A BMI of ≥ 45 or 50 kg/m2 is super obesity.

As Asian populations develop negative health consequences at a lower BMI than Caucasians, some nations have redefined obesity; Japan has defined obesity as any BMI greater than 25 kg/m2[8] while China uses a BMI of greater than 28 kg/m2.[29]