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.

Obesity increases the likelihood of various diseases, particularly, heart disease, type 2 diabetes, obstructive sleep apnea, and certain types of cancer, osteoarthritis and asthmas. Obesity is most commonly caused by a combination of excessive food allergy intake, lack of physical activity, and genetic susceptibility, although primarily genes, endocrine disorders, medications or psychiatric illness cause a few cases. 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.

Healthy eating and physical exercise are the mainstays of treatment 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. Anti-obesity drugs may be taken to reduce appetite or inhibit fat absorption together with a suitable diet. 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 earlier satiation and reduced ability to absorb nutrients from food. Obesity is a leading preventable cause of death worldwide.