Nutrition, aging and obesity: a critical review of a complex relationship.

Long-standing beliefs about the ill-effects of mild to moderate obesity have been called into question by recent epidemiological studies and by critical review of older studies. A review of these studies reveals that the effects of obesity on health and longevity is more complex than we had realized. An attempt is made to throw light on this relationship by reviewing the large number of laboratory studies on nutrition, aging and obesity. The first series of such studies showed that restriction of food intake, beginning early in life, greatly increased longevity. A second series of studies revealed that longevity could still be extended even if restriction of food intake did not occur until maturity. The third series of studies showed that dietary constituents as well as total calories influenced longevity. High-fat diets produce obesity and a shortened life span and there are significant differences in the effects of other dietary constituents at different times in the life cycle. The fourth series of studies, on dietary self-selection. are beginning to elucidate the role of food preferences in determining both obesity and longevity. Potential mechanisms of action include both body weight and immunological processes.