Feeding behavior in monkeys with and without lesions of the hypothalamus

In monkeys (Macaca mulatta) without hypothalamic lesions, food intake was found to increase with increasing age and body weight; however, food intake per kilogram body weight showed a decline over the same period of time. As the animals became older, the amount of food intake converted to body weight decreased dramatically (feeding efficiency). Water intake was shown to be closely coupled to food intake. Both daily food and water-intake data were highly reliable over a period of years. Monkeys with ventromedial hypothalamic lesions exhibited hyperphagia and increased feeding-efficiency ratios and eventual obesity. The obese animals developed symptoms of diabetes mellitus. Animals with lesions restricted primarily to the arcuate nucleus showed no hyperphagia but increased feeding efficiency. These animals exhibited decreased growth hormone release and a transitory elevation of serum insulin.