Regulation of energy balance in two models of reversible obesity in the rat.

Adult male rats were made obese either by tube feeding varying fractions (34%, 47%, 68% or 75%) of their normal food intake or by offering them a varied and palatable diet (cafeteria diet). After 17--30 days of these regimens, the treatments were withdrawn, and the animals were allowed free access to the normal stock diet. Tube-fed animals precisely adjusted voluntary food intake to compensate for the energy delivered by tube but nevertheless became obese as a result of an increased metabolic efficiency. Cafeteria-fed rats were hyperphagic and became obese without any apparent change in metabolic efficiency. Recovery from obesity was more rapid in the cafeteria animals and was due to a pronounced increase in heat production as well as concomitant hypophagia. Animals previously made obese by tube feeding exhibited hypophagia and returned to normal weight without any change in heat production. The relevance of these results to the concept of lipostasis and the relative roles of energy intake and expenditure in the regulation of energy balance are discussed.