Caffeine enhances performance regardless of fueling strategy, however high CHO availability is associated with improved training speeds compared with ketogenic diet

Abstract The purpose of this study was to confirm reduced training metrics previously associated with a ketogenic low-carbohydrate (CHO) high-fat diet (LCHF) and investigate their attenuation with caffeine supplementation. At baseline, n =21 elite race-walkers followed a high CHO availability (HCHO) diet and performed a tempo hill session (14 km with a 450 m elevation gain). Athletes were then assigned to either the HCHO or LCHF in a parallel groups design for 3 weeks where the 14 km tempo hill session was repeated each week. On weeks 2 and 3, in a randomized crossover allocation, all participants received 3 mg/kg caffeine or placebo (gum), 20 min before the session. Race-walking speed, heart rate, RPE, blood metabolites and Stroop word-color test metrics were collected. Although LCHF athletes walked faster at baseline compared to HCHO ( p =0.049), the HCHO group improved by week 2 ( p =0.009) and week 3 ( p =0.007) whereas the LCHF group were significantly slower in Week 1 ( p <0.001) and Week 2 ( p =0.026) compared to Baseline. During the 14 km hill session, within-group analysis shows that athletes walked significantly faster ( p =0.010) and at a higher percentage of vVO 2 max ( p =0.007) when using caffeine compared to a placebo. Between-group differences remained present, with HCHO athletes walking at a higher percentage of vVO 2 max than those adhering to the LCHF diet ( p =0.035). No interaction between supplement treatment and dietary group occurred ( p =0.640). Caffeine supplementation partially reversed the performance impairment associated with an LCHF diet, but training quality remained lower than the combination of caffeine and high CHO availability.