Body fat phenotypes are determined by the “genetic lottery of life” and socioenvironmental factors.

A complex interplay between random genetic and epigenetic factors and social and environmental factors determines human fatness. In restrictive environments, i.e., environments where high energy expenditure is required to obtain few calorie-poor foods, variation in body weight is low simply because a subchronic negative energy balance prevents obesity-prone individuals from putting on weight. Conversely, obesogenic environments are characterized by high availability of hyperpalatable foods, and minimal physical efforts are required to obtain the next calorie-dense meal. Such environments reveal (1) parts of the population that are genetically predisposed to obesity (obesity prone), (2) individuals that only put on a moderate amount of fat mass (intermediate), and (3) individuals who have inherited a genetic “advantage” that allows them to stay lean (obesity resistant).