|Classification and external resources| Silhouettes and waist
circumferences representing normal, overweight, and obese
Obesity is a medical condition in which excess body fat has
accumulated to the extent that it may have an adverse effect on
health, leading to reduced life expectancy and/or increased
health problems. People are considered obese when their body
mass index (BMI), a measurement obtained by dividing a person's
weight in kilograms by the square of the person's height in
metres, exceeds 30 kg/m2. Obesity increases the likelihood of
various diseases, particularly heart disease, type 2 diabetes,
obstructive sleep apnea, certain types of cancer, and
osteoarthritis. Obesity is most commonly caused by a combination
of excessive food energy intake, lack of physical activity, and
genetic susceptibility, although a few cases are caused
primarily by genes, endocrine disorders, medications or
psychiatric illness. Evidence to support the view that some
obese people eat little yet gain weight due to a slow m