Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes

Background. Low-carbohydrate diets have recently grown in popularity among endurance athletes, yet little is known about the long-term (>4 wk) performance implications of consuming a low-carbohydrate high fat ketogenic diet (LCKD) in well-trained athletes. Methods. Twenty male endurance-trained athletes (age 33 +/- 11 y, body mass 80 +/- 11 kg; BMI 24.7 +/- 3.1 kg/m(2)) who habitually consumed a carbohydrate-based diet, self-selected into a high-carbohydrate (HC) group (n = 11, %carbohydrate:protein:fat = 65:14:20), or a LCKD group (n = 9, 6:17:77). Both groups performed the same training intervention (endurance, strength and high intensity interval training (HILT)). Prior to and following successful completion of 12-weeks of diet and training, participants had their body composition assessed, and completed a 100 km time trial (TT), six second (SS) sprint, and a critical power test (CPT). During post-intervention testing the HC group consumed 30-60 g/h carbohydrate, whereas the LCKD group consumed water, and electrolytes. Results. The LCKD group experienced a significantly greater decrease in body mass (HC-0.8 kg, LCKD-5.9 kg P = 0.006, effect size (ES): 0.338) and percentage body fat percentage (HC-0.7%, LCKD-5.2%; P = 0.008, ES: 0.346). Fasting serum beta-hydroxybutyrate (beta HB) significantly increased from 0.1 at baseline to 0.5 mmol/L in the LCKD group (P = 0.011, ES: 0.403) in week 12. There was no significant change in performance of the 100 km TT between groups (HC-1.13 min-s, LCKD-4.07 mins, P = 0.057, ES: 0.196). SS sprint peak power increased by 0.8 watts per kilogram bodyweight (w/kg) in the LCKD group, versus a -0.1 w/kg reduction in the HC group (P = 0.025, ES: 0.263). CFI peak power decreased by-0.7 w/kg in the HC group, and increased by 1.4 w/kg in the LCKD group (P = 0.047, ES: 0.212). Fat oxidation in the LCKD group was significantly greater throughout the 100 km TT. Conclusions. Compared to a HC comparison group, a 12-week period of keto-adaptation and exercise training, enhanced body composition, fat oxidation during exercise, and specific measures of performance relevant to competitive endurance athletes. (C) 2017 Elsevier Inc. All rights reserved.