ACUTE EFFECTS OF HIGH-FAT AND HIGH GLUCOSE MEALS ON THE GROWTH-HORMONE RESPONSE TO EXERCISE

The health promoting, anabolic effects of physical activity may be med iated, in part, by an exercise-associated increase in GH. However, lit tle is known about the acute effects of diet on exercise-induced GH re lease. We hypothesized that a single meal could attenuate the GH respo nse to exercise by modulating substances like somatostatin, insulin, o r glucose. Eleven healthy young adults performed 10 min of high intens ity, standardized cycle ergometry in the morning following an overnigh t fast. On separate days they ingested a noncaloric placebo liquid mea l or an isovolemic, isocaloric liquid meal high in either fat or gluco se. Venous blood samples were obtained before and for 90 min after exe rcise began, whereas gas exchange data were measured breath by breath. Peak mean oxygen consumption (VO2) was, on average, 9-fold greater th an preexercise levels in all groups. Although there was no difference in preexercise GH levels, mean peak, postexercise GH was 54% lower aft er the high-fat meal compared with placebo (P < 0.01). Modest decrease s in GH response to exercise after the high-glucose meal were not stat istically significant. Mean serum somatostatin was significantly highe r after the high-fat meal compared with both high glucose and placebo meals. This study demonstrates that exercise-induced GH release can be significantly attenuated by the contents of a single preexercise meal . The high fat meal increased circulating somatostatin and was associa ted with an inhibition of the GH secretion. The data provide a possibl e specific mechanism to explain how diet can acutely modulate the anab olic effects of exercise.