ABSTRACT
This chapter aims to examine the effects of weight loss and regain, particularly when such cycles occur repeatedly. It reviews figures on the prevalence of dieting and discusses the possible effects on both behavior and metabolism. Basic laws of thermodynamics indicate that energy intake must equal energy expenditure or weight will change. Weight will increase if intake exceeds expenditure and will decrease if expenditure exceeds intake. The chapter provides data from human studies and then from the animal literature. Weight loss would require greater and greater degrees of caloric restriction, perhaps producing the individuals who lose far less weight than predicted, even on strict diets. Lowered metabolic rate appears to be one mechanism for the energy conservation that accompanies dieting. Lipoprotein lipase (LPL) is considered the gatekeeper enzyme responsible for incorporation of lipid into fat cells, so when LPL activity is increased, more fat is stored given available circulating lipid.
