Energy expenditure in rats with diet-induced obesity.

Effects of a diet high in fat on body weight, adiposity, and energy expenditure were investigated. Male rats were fed 8% (control) or 50% fat (by weight) for 6 mo. The high-fat group increased body weight (+26%), adipocyte size (+61%), and adipocyte number (+48%). However, food intake and resting oxygen consumption, although higher in absolute amount, were normal in that both were commensurate with the greater body mass the rats maintained. When body weight and adipocyte size were reduced by caloric restriction, the high-fat group displayed the same adaptive adjustments in resting oxygen consumption as controls. We conclude that rats fed high-fat diets for prolonged periods 1) have energy intakes and expenditures appropriate for the greater tissue mass and adipocyte number they maintain, and 2) show adaptive reductions in energy expenditure when food is restricted, which provide further evidence that the regulated level of body weight can be altered by such diets.