It is clear that the development of obesity cannot be adequately explained as just a lasting enforced positive energy balance. Much more complex interacting mechanisms are operating making predictions based on energy balance difficult if at all possible: appetite (hunger and satiety), energy metabolism, physical activity, body fat distribution (abdominal versus lower body), development of adipose tissue, regulation of fatty acids deposition and release, and synthesis and secretion of regulatory substances from this tissue. This study hypothesizes, that inter-individual differences on body weight gain (including resistance to weight loss and risk of weight regain after weight loss), and in the responses to dietary interventions may originate in genes in which variants lead to different susceptibility to various dietary factors.