This term derives from the Latin (obesus, meaning "to eat up"), and it came into use in English in the early 1600s to mean a condition characterized by excessive bodily fat. Excess body weight is associated with the increased storage of energy in the form of adipose tissue. Standard criteria for obesity are (1) greater than 20 percent above ideal body weight (IDW) for a given height, as determined from actuarial tables, or (2) body mass index (BMI), defined as weight in kilograms divided by height in meters squared (kg ÷ m² = BMI), greater than 27 for men and greater than 25 for women.

Obesity represents the upper end of a bodyweight continuum, rather than a qualitatively different state. Obesity can derive from a variety of causes, but a significant genetic contribution has been demonstrated.

Being overweight to a statistically significant above-average degree or having proportionately more body fat than average is believed to...