Diet-induced hyperphagia in the rat is influenced by sex and exercise

Caloric intake is increased in rats fed a diet containing greater fat or sugar than that found in laboratory chow. Because such diet-induced hyperphagia has been studied primarily in sedentary male rats, our goal here was to investigate the effects of sex and exercise on caloric intake of a diet (chow supplemented with sweet milk) chosen for its ability to stimulate hyperphagia. Rats were housed individually in cages that provided access to running wheels, and daily caloric intake of chow alone and then chow plus sweet milk was monitored during sedentary and active conditions. In sedentary rats, chow intake was greater in males compared with females. Wheel running produced similar decreases in chow intake in both sexes. Availability of the chow plus milk diet increased caloric intake compared with that observed in chow-fed rats. This diet-induced hyperphagia was significantly greater in sedentary females (35.7 +/- 3.1% increase) relative to sedentary males (9.1 +/- 2.2% increase). In addition, 35% of sedentary females consuming the chow plus milk diet developed estrous cycle disruptions. Wheel running decreased intake of the chow plus milk diet in both sexes. In active males, diet-induced hyperphagia was abolished; caloric intake was reduced to that observed during chow feeding. In active female rats, diet-induced hyperphagia was attenuated but not abolished; caloric intake of the chow plus milk diet remained greater than that observed during chow feeding. We conclude that female rats are more vulnerable than male rats to this form of diet-induced hyperphagia.