Influence of Diet on the Response of GH-IGF-I Axis and Ghrelin Secretion during Endurance Exercise in Trained Athletes

Abstract

1495 The consequences of long lasting physical exercises and/or negative energy balance are e.g. hypoglycemia and enhanced free fatty acids, which are known to stimulate growth hormone (GH) secretion. Ghrelin, mainly produced in the upper gastrointestinal tract, is a potent secretagogue of GH. Negative energy balance (fasting) enhances Ghrelin secretion and positive energy balance results in low Ghrelin levels. PURPOSE: To determine as it is currently unknown, whether a) aerobic exercise impacts on Ghrelin secretion, b) Ghrelin regulates GH secretion during exercise and c) different quality of food affect GH and Ghrelin concentrations during aerobic exercise. METHODS: Eleven healthy endurance trained male cyclists or triathletes (age: 31.4 ± 5.7 years, mean ± SD; BMI: 22.6 ± 1.7 kg/m2; VO2 peak: 63 ± 7 ml/min/kg BM; maximal workload (Wmax) 365 ± 29 Watts) were investigated twice in a randomised crossover design following two types of diet: low fat diet (LF: fat <0.5g/kg BM during 2.5 days) and high fat diet (HF; fat <0.5g/kg BM during 1 day followed by fat 3.5g/kg BM during 1.5 days). Carbohydrate intake was standardised on both occasion (7g/kg BM/d for 3 days). The food was preweighed and packed by meal. Subjects attended the investigation unit in the morning. Baseline measurements for GH, IGF-I and Ghrelin were drawn and Ghrelin and GH concentrations were assessed at regular intervals throughout a 3hours aerobic exercise test on a bicycle-ergometer at 50% of Wmax (170–200 Watts). RESULTS: Mean GH concentrations significantly increased (p<0.001) with a peak level within the first hour of exercise. Diet did not significantly impact on GH concentrations (Area under the curve – AUC-GH: LF vs HF diet, p = 0.8). Ghrelin concentrations significantly increased (p<0.03) during exercise and appeared to plateau in the last hour of exercise. LF diet resulted in a significant increase in Ghrelin concentrations compared to HF diet (AUC-Ghrelin: LF vs HF, p<0.04). Baseline IGF- I concentrations did not significantly change after either diet. No correlations were observed between GH and Ghrelin secretion. CONCLUSION: This data suggest that a) Ghrelin does not correlate, neither directly controls GH secretion during aerobic exercise, b) Ghrelin may be involved in energy homeostasis and c) regulation of Ghrelin secretion may depend on nutrients. Supported by Swiss National Fund (3200BO-100146/1).