Hormonal Response to Prolonged Endurance Exercise in Elite Keto-Adapted Ultra-Endurance Athletes
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Date
2017-03
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Abstract
Objective: A burgeoning body of empirical and experimental evidence indicates that nutritional ketosis induced by carbohydrate restriction has clinical and physical performance applications. We recently reported that elite keto-adapted endurance athletes had greater than two-fold higher rates of fat oxidation, yet muscle glycogen at rest and after exercise was the same as a matched group of high-carbohydrate athletes. Given the importance of endocrine regulation of substrate mobilization and oxidation, the purpose of this study was to compare hormonal profiles to prolonged exercise in keto-adapted and high-carbohydrate athletes. Methods: Low Carbohydrate (n=10) and High Carbohydrate (n=10) ultra-endurance athletes, in the top 10% of race finishers, were enrolled for participation in this study. Participants completed body composition assessment via dual energy x-ray absorptiometry followed by a 180-min treadmill run at 64% VO2max. Venous blood sampling was obtained pre, during, and up to 2 hr post-exercise to assess testosterone, insulin-like growth factor 1, growth hormone, insulin like growth factor binding protein 1, glucagon, leptin and cortisol. Baseline hormone concentrations and body composition differences were assessed via independent t-tests. Biochemical responses to exercise and diet were assessed via a 2-way repeated measures analysis of variance. Results: No significant differences existed between groups in body composition. Resting plasma growth hormone concentrations in keto-adapted athletes were 3.5-fold higher (P<0.05). Glucagon concentrations were significantly higher in all but one timepoint for low carbohydrate athletes. A significant main effect of time, but not diet, was observed for testosterone, insulin-like growth factor 1, growth hormone, insulin like growth factor binding protein 1, and cortisol. Normalized testosterone and insulin like growth factor 1 demonstrated trends for higher concentrations in the low carbohydrate group post-exercise. Conclusion: The pronounced shift to lipid oxidation at rest and during submaximal exercise in keto-adapted athletes is accompanied by a differential endocrine response characterized by elevated growth hormone and glucagon and decreased leptin concentrations.
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Education and Human Ecology: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
Keywords
Ketogenic, Athletes, Endocrinology, Metabolism