NUTRITION PLAYS A MAJOR ROLE IN THE GH??F-I RESPONSE TO EXERCISE.

Abstract

Brief bouts of strenuous exercise can cause inhibition of the growth hormone (GH)→ insulin-like growth factor-I (IGF-I) axis. Smith et al. (Metabolism 1987;36:533) showed that strenuous exercise training further reduced the circulating IGF-I when associated with a low calorie, low protein diet. But after 5 weeks of training, children and adolescents even with unrestricted access to food demonstrated reduced circulating levels of IGF-I (Pediatric Res 2002;52:491). These observations led us to hypothesize that exercise training would lead to a reduction in circulating IGF-I even under conditions of clearly adequate calorie and protein intake. PURPOSE: We hypothesized that a catabolic-type hormonal response (i.e., a decrease in IGF-I) will invariably occur with strenuous exercise training even if caloric intake exceeds total energy expenditure. METHODS To test this we examined the combined influence of diet and exercise training on growth mediators and inflammatory cytokines in 22 young healthy male adults. All participated in a 7-day strenuous exercise program (3 hours a day). Subjects were randomly assigned to one of two groups: positive energy balance (calorie supplemented); or negative energy balance (calorie restricted). RESULTS 19 subjects completed the study (9 restricted, 10 supplemented). The restricted group had an average weight loss of −1448±246 g (p < 0.0001) while the supplemented group gained 890±270 g (p < 0.009). IGF-I initially decreased in both groups; but from day 3 it continued to decrease only in the restricted group (p < 0.0005, Fig).Figure: No Caption AvailableCONCLUSIONS Caloric supplementation may attenuate or even prevent the initial catabolic response associated with exercise. In contrast to our hypothesis, diet seems to play a major role in the regulation of the longer-term GHÌF-I response to exercise training. Sponsored by NIH grants MO1-RR00827 and HD 23969. Dr. Nemet is a postdoctoral fellow of the Joseph E. Drown foundation.