Previously, rats fed a high-fat liquid diet (HF) ad libitum consumed more kilocalories and had greater weight gain than rats fed a liquid high-carbohydrate diet (HC) of equivalent energy density (Warwick, Z. S., and H. P. Weingarten. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 269: R30-R37, 1995). The present series of experiments sought to clarify the behavioral expression of HF hyperphagia by comparing HF and HC with regard to meal size and magnitude of postingestive satiety effect. Meal size of HF was greater than HC at 2.3 kcal/ml and also when diets were formulated at 1.15 kcal/ml. In a preload-test meal paradigm, an orally consumed HF preload was less satiating than a calorically equivalent HC preload across a range of preload volumes and intermeal intervals. Sensory-specific satiety was ruled out as an explanation of the relatively greater intake of test meal after an HF preload meal; an intragastrically delivered HF preload was less satiating than intragastric HC. Furthermore, a fat (corn oil emulsion) preload was less satiating than a carbohydrate (sucrose) preload when an evaporated milk test meal was used. These findings indicate that hyperphagia on an HF diet is expressed in increased meal size and decreased intermeal interval.

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Previous studies comparing the effect of supplemental full-fat and reduced-fat foods on weight gain have yielded inconsistent findings: Sclafani et al.' found that rats fed a single high-fat option (cake) gained more weight than rats fed no-fat cake, whereas Harris2 found no difference in the weight gain of rats fed high-fat versus low-fat cafeteria foods. The purpose of the present study was to further compare the weight gain of rats fed supplemental high-fat foods to that of rats fed the reduced-fat versions of these foods. METHODTwo weight-matched groups of male Long-Evans rats (n = 7 or 8 per group, average weight 264 grams) were given an option food daily in addition to Purina chow for 29 days. Group FF received full-fat option foods. Group RF received reduced-fat option foods (TABLE 1). Only one food was provided per day. At the end of 24 hours, the remaining option food was removed, and a different option was given. A control group received only chow. Body weights were measured weekly. RESULTSBody weight gains are depicted in FIGURE 1. Repeated measures ANOVA on body weight gain revealed a significant group x days interaction, F(6.48) = 7.87.Student-Newman-Keuls post hoc tests, when appropriate, were then conducted to identify significant differences between groups. CONCLUSIONSRats fed either a full-fat option (group FF) or a reduced-fat option (group RF) in addition to chow gained significantly more weight than chow-fed controls.