Sex differences in the relationship between activity and weight loss in the rat

Access to a running wheel combined with restricted feeding produced body we ight loss at an equivalent rate in male and female litter-mate rats (Experi ment 1). Thus, despite weighing less and running more, females were not mor e vulnerable to this procedure. When factors influencing weight loss were v aried, no sex difference was found in adaptation to a new feeding schedule or in the effect of single versus group housing (Experiment 2). The apparen t critical difference was that body weight loss increased running in males but not in females (Experiment 3). In all rats, rapid recovery of body weig ht occurred when food access was no longer restricted (Experiment 1), sugge sting that "activity-based anorexia" is a misnomer for weight loss by rats in a running wheel.