DAILY EXERCISE REDUCES FAT, PROTEIN AND BODY-MASS IN MALE BUT NOT FEMALE RATS

This study was designed to compare the estimated energy balance, linea r growth (body and bone lengths) and body composition (all components including body mass, total body water, fat, protein and ash) response to daily spontaneous running (DSR) in young male and female rats. We t ested the hypothesis that due to gender differences in energy efficien cy, DSR would reduce linear growth and body composition more in male r ats. Fourteen male and sixteen female weanling Sprague-Dawley rats wer e randomly assigned to either a sedentary (SED) control (male 7, femal e 8) or DSR (male 7, female 8) group. The DSR rats were allowed to run spontaneously in running wheels while SED rats remained in standard r at cages for 9 weeks. Body mass, running distance and food intake were measured over the nine week period. subsequently, chemical analysis w as performed to measure carcass content of water, protein, fat and ash . Linear growth was assessed by measures of body and bone lengths. The estimated energy balance of the DSR rats was computed and compared be tween genders. Estimated energy balance was significantly more negativ e in females than males due to significantly greater DSR distance. Bod y and bone lengths were similar among the SED and DSR female and SED a nd DSR male rats. However, whole body mass, fat mass and protein mass were significantly lower only in DSR males. These results demonstrate that DSR reduced body mass, body fat and protein mass in male rats but not in female rats despite a more negative estimated energy balance i n female rats. These findings suggest that females are better protecte d from an energy deficit due to DSR. Possible mechanisms include gende r-specific hormonal responses. (C) 1997 Elsevier Science Inc.