Modern concepts of obesity

Recent advances in the classification, etiology, treatment, and theoretical approaches to obesity are reviewed. Human and animal studies are summarized, as they relate to these categories of obesity research. Special attention is given to the possible multiple etiologies of obesity and the roles of diet and exercise in weight control. Possible mechanisms underlying inevitable weight regain in reduced obese individuals are discussed relative to cellular and metabolic processes that function in adipose tissue. An hypothesis (termed "the ratchet effect") is offered which suggests than an irreversible increase in adipocytes in some obese subjects may produce increasingly elevated body fat stores that provide a resistance to significant weight reduction. Inferences are drawn for future therapeutic approaches and research directions for obesity attenuation. (wz)