SummaryThe effect of bilateral destruction of the ventromedial hypothalamus (VMH) on protein and energy intakes was examined in relation to protein utilization. In Experiment 1, rats with VMH lesions were allowed to select protein (either casein or wheat gluten) and energy from two diets containing 70% and 5% protein, respectively. In Experiment 2, they were restricted to 0,100 and 200mgN/day of protein and given free access to protein-free diet. In Experiment 3, they were restricted to 2 and 5g/day of protein-free diet but given 92% protein diet ad libitum. Self-selecting rats with VMH lesions consumed about 100kcal/day regard less of the protein source, in contrast to sham-operated controls which consumed 75kcal/day. They showed increased non-protein energy intake with constant protein consumption resulting in normal protein retention with increased body fat. When protein intake was restricted to 200mgN/ day, energy intake was reduced in animals given diet containing wheat gluten more than in those given diet containing casein, resulting in lower protein utilization. Therefore, food intake depended upon the amount of dietary protein. Rats with VMH lesions showed an exaggerated response to the ratio of protein to energy in the diet and consumed more energy from balanced diet but showed more reduction in food intake than controls in response to diet with an inappropriate ratio of protein to energy. The present study confirmed that the VMH was related to regulation of energy intake but not protein intake. It is suggested that protein intake is regulated in relation to maintenance of body protein in rats with VMH lesions as well as in normal rats. Key Words self-selection, protein restriction, energy restriction, protein utilization, protein intake regulation, VMH lesion Bilateral destruction of the ventromedial hypothalamus (VMH) produces the characteristic symptoms of hyperphagia, hyper-reactivity to palatability of the diet, and hormonal and metabolic alterations associated with enhanced accumulation of body fat (for recent review see (1)). From the symptom of hyperphagia, this locus has been recognized as the "satiety center" and the hypothesis of a dual center of food intake has been established (2).It is well known that both the quality and quantity of protein in the diet affect food intake. Food intake of rats with VMH lesions as well as of intact rats is depressed in response to a diet with excess of a single amino acid (3), with an imbalance of amino acids (3, 4), and with a high protein content (3, 5). Moreover, Rozin (6), Musten et al. (7), and Kishi et al. (8) suggested that the regulations of protein intake and energy intake are different. Anderson et al. (9) concluded from a study on self-selection of diet that regulation of protein intake was normal in both hypothalamic hyperphagic and obese Zucker rats. The mechanism of regulation of protein and amino acid intakes is still unknown, but although direct evidence is still lacking, the VMH is not supposed to be involved.From the nutritional point of vi...