RESTRICTED FEEDING AND BONE MASS IN AN ANIMAL MODEL OF THE FEMALE ATHLETE TRIAD

Abstract

Previous work in this laboratory demonstrated that female rats, restricted-fed to persistent anestrus and allowed unlimited access to running wheels, had significantly lower total body and femoral BMC and BMD compared to ad libitum-fed rats. Also, and libitum-fed rats, with unlimited access to running wheels, had significantly greater total body and femoral BMD and BMC compared to sedentary rats. PURPOSE To examine the effects of dietary restriction and exercise on bone mass in female rats. METHODS Twenty-two female Sprague-Dawley rats (age 40 days) were randomly assigned to four groups: ad libitum-fed running, ad libitum-fed sedentary, restricted-fed running, and restricted-fed sedentary. Running rats were individually housed with digitally monitored running wheels. Rats were fed pelleted AIN-G chow. Beginning at 159 days, the restricted-fed rats were subjected to 30% dietary restriction to initiate weight loss and anestrus. After 60+ days in anestrus (day 280), total body and femoral BMD and BMC were measured by dual-energy x-ray absorptiometry. Separate ANOVAs were used to examine the effects of feeding and exercise on BMD and BMC. RESULTS There were significant main effects (p < 0.05) for feeding and exercise on body mass such that ad libitum-fed and running rats had significantly greater body mass compared to restricted-fed and sedentary rats. Prior to normalizing for body mass, restricted-fed and sedentary rats had significantly less femoral BMD than ad libitum-fed and running rats. However, when normalized for body mass, restricted-fed and sedentary rats had significantly greater femoral BMD and BMC compared to ad libitum-fed and running rats. Feeding and exercise explained 65–85% and 21–56% of the variability in bone mass, respectively. CONCLUSION These findings suggest that the bone loss observed in the restricted-fed rats may have been due primarily to weight loss rather than anestrus.