Preferential fat intake increases adiposity but not body weight in Sprague-Dawley rats

It is not known whether an inherent preference for dietary fat promotes obesity in animals allowed to self-select the proportions of fat and carbohydrate consumed. To address this question, Sprague-Dawley rats were given a choice between two diets containing either 78% fat (by energy) or 78% carbohydrate; both diets were equicaloric for protein (22%). The entire study lasted 12 weeks. After an adaptation period, macronutrient preferences were determined by measuring 24 h intake of the two diets for 5 days; fat-preferring animals were classified as those that consumed greater than 60% of total energy from the fat/protein source, and carbohydrate-preferring rats as those that consumed less than 40%. Rats with intermediate macronutrient intakes were excluded. Initial body weight was not different between preference groups. Caloric intakes and body weights were then recorded at approximate weekly intervals, and fat depots were weighed at the time of sacrifice. Measures of energy intake and body weight did not differ between the two preference groups over time. In addition, baseline macronutrient preferences remained stable across the study period. Despite similar body weights, mean epididymal fat depot weight was significantly higher in fat-preferring rats than in carbohydrate-preferring rats (12.6 vs. 10.0 g); also, mean inguinal fat depot weight in fat-preferrers was greater although not reliably different compared to carbohydrate-preferring rats (12.9 vs. 10.9 g). Thus, the preferential intake of fat led to a greater deposition of both subcutaneous and visceral fat without an increase in body weight. These data lead us to conclude that the increased fat deposition was due primarily to the ingestion of fat rather than to excess caloric intake.