Dietary fat content affects energy intake and weight gain independent of diet caloric density in rats

Recent considerations of high-fat diet hyperphagia have focused on fat's relatively high energy density as the critical variable which promotes overeating. However, a high-fat (HF) diet has been shown to enhance intake and weight gain relative to a high-carbohydrate (HC) diet when both energy density and palatability are equated [Am. J. Physiol. 269 (1995) R30]. The present studies investigated the generality of this finding across manipulations of diet caloric density, diet physical form, and chow availability. Separate groups of male rats were fed HF or HC at either 2.3 or 1.15 kcal/ml for 16 days; HF feeding enhanced weight gain relative to HC across both levels of energy density. HF hyperphagia also occurred when diets were presented in semisolid (gelled) form, and when chow was available in addition to liquid diet. These findings are consistent with previous observations that an HF diet can enhance daily kilocalorie intake and weight gain at least partly via a mechanism that is unrelated to caloric density.