The determinants of obesity can be divided into the genetic, the environmental, and the regulatory. For example, mutations in the ob gene have led to massive obesity in mice. The existence of leptin supports the idea that body weight is regulated, because leptin serves as a signal between adipose tissue and the areas of the brain that control energy metabolism, which influences body weight. The extent of genetic influences on human obesity has been assessed by twin, adoption, and family studies. This influence is dramatically illustrated by the marked increase in the prevalence of obesity in the past decade.
Socioeconomic status is an important influence on obesity, particularly among women.
The negative correlation between socioeconomic status and obesity reflects an underlying cause. Longitudinal studies have shown that growing up with lower socioeconomic status is a powerful risk factor for obesity. Socioeconomic factors are major influences on both energy intake and energy expenditure. A large food intake is associated with obesity. For many years, it was believed that obscure metabolic disturbances caused obesity and that food intake was normal.