The genetics of obesity: what have genetic studies told us about the environment.

Genetic studies have shown that both childhood and adult body mass index are substantially heritable. The evidence for shared family environmental influences is largely absent, even though there are clear indications that secular changes in energy expenditure have brought about a significant increase in the prevalence of obesity. This apparent inconsistency may be explained by the dual phenomena of the near-universality of access to environments that facilitate reductions in energy expenditure (e.g., TV as a recreational pastime), together with heritable individual differences in the response to or utilization of these environments. The impact of changes in nonshared environments on body weight can be estimated from biometrical genetical studies and is found to be both small and relatively short-lived. Genetic and environmental results from longitudinal studies are consistent with what is known about the changing distribution of adiposity during adulthood and clinical experience of the difficulty of maintaining behavioral-induced weight loss.