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 illness.[5] Evidence to support the view that obese people eat little yet gain weight due to a slow metabolism is not generally supported.[6] On average, obese people have a greater energy expenditure than their thin counterparts due to the energy required to maintain an increased body mass.[6][7]