The effect of body fatness on the maintenance energy requirements of adult rats

In the first experiment adult rats were allowed access to different amounts of diet of high energy density and were allowed to grow until there was a spread of bodyweights of 100 g. Of this difference 50% was fat and 10% was protein. Intakes were then adjusted to maintain a constant bodyweight and energy balance was assessed from changes in body composition. In the second experiment rats were force-fed on excess food for different times and their heat production was estimated by closed-circuit indirect calorimetry. Two groups were overfed and then deprived of food until they reached their initial bodyweight. One of those groups had a protein supplement during the period of weight reduction in an attempt to maintain body protein under negative energy balance. It is concluded that when the main variable is body fat, differences in heat production at energy equilibrium and in deprivation are proportional to bodyweight 0.75. If the conclusion is proved in other animals it has important implications for the interpretation of many experiments in normal and obese animals..