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 mediated, in part, by an exercise-associated increase in GH. However, little is known about the acute effects of diet on exercise-induced GH release. We hypothesized that a single meal could attenuate the GH response to exercise by modulating substances like somatostatin, insulin, or glucose. Eleven healthy young adults performed 10 min of high intensity, standardized cycle ergometry in the morning following an overnight fast. On separate days they ingested a noncaloric placebo liquid meal or an isovolemic, isocaloric liquid meal high in either fat or glucose. Venous blood samples were obtained before and for 90 min after exercise began, whereas gas exchange data were measured breath by breath. Peak mean oxygen consumption (VO2) was, on average, 9-fold greater than preexercise levels in all groups. Although there was no difference in preexercise GH levels, mean peak, postexercise GH was 54% lower after the high-fat meal compared with placebo (P < 0.01). Modest decreases in GH response to exercise after the high-glucose meal were not statistically significant. Mean serum somatostatin was significantly higher 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 associated with an inhibition of the GH secretion. The data provide a possible specific mechanism to explain how diet can acutely modulate the anabolic effects of exercise.