Caloric intake and weight gain of rats depends on endogenous fat preference

Within outbred colonies, subpopulations of rats exist that exhibit inherent preferences for one type of macronutrient over another (e.g., fat vs. carbohydrate). Prior investigations into the effect of dietary manipulations on consumption or weight gain have not taken into account endogenous macronutrient preferences. The purpose of this study was to examine whether inherent fat preferences translate into differences in caloric consumption and weight gain in rats whell fed high-fat and high-carbohydrate diets. Rats that exhibited a preference for fat were identified using a previously described paradigm and were subsequently placed on either a high-fat or high-carbohydrate diet. Daily caloric intakes and weekly weights were monitored over a 28-day period and compared with data for animals with a low-fat preference on the same diets. By the conclusion of the study, the low-fat-preferring rats on the high-carbohydrate diet had consumed significantly more calories than the high-fat-preferrers maintained on the same diet. In contrast, the amounts of calories consumed on the high-fat diet were not significantly different between the low- and high-fat-preferring animals. Those animals with a preference for fat placed on a high-carbohydrate diet weighed significantly less by the end of study, even though they consumed the same number of calories as animals on the high-fat diet. We conclude that the outcome of nutritional studies designed to examine caloric intake and weight gain can be influenced by the innate macronutrient preference of the animal.