Obesity is a complex disease influenced by genetic and environmental factors and by their interaction. The most quoted theories attribute the current worldwide surge of obesity in both adults and children to the interaction between a genetic predisposition toward efficient energy storage, which is the legacy of the ancestral hunter-gatherer society, and a permissive (obesogenic) environment of readily available food and sedentary behaviors as it is the modern environment. This genetic predisposition, commonly described as “thrifty genotype” (Neel 1962), is nowadays maladaptive, increasing the individual predisposition to obesity and related metabolic disorders.