Effect of a high carbohydrate pre-exercise meal on metabolic and performance-related parameters in male athletes following two different strategies to improve fat utilization

Abstract Background In a preliminary investigation, a long-term diet rich in low glycaemic carbohydrates (LGI) led to an improved metabolic flexibility and exercise performance compared to the high fat low carbohydrate (HFLC) diet. Since the exercise tests were performed in the fasted state, it cannot be concluded how these two different nutritional strategies affects the metabolism, if they are combined with a carbohydrate restoration phase prior to the exercise. Methods The influence of a carbohydrate-rich pre-exercise meal on metabolic and performance-related parameters was investigated in a group of male endurance athletes, who had previously followed either a HFLC (n = 6) or LGI (n = 6) diet for 4 weeks. Participants continued their regular training routine during the intervention to assess exclusively the effect of the nutritional strategies on metabolic and performance-related parameters. Respiratory exchange ratio (RER), lactate concentrations, substrate oxidation rates at rest and during a cycle ergometry with incremental workload were determined in the fasted state and 2 h after consuming a carbohydrate-rich (2 g per kg of body mass) pre-exercise meal. Power output at lactate thresholds, peak oxygen uptake (V̇O2peak), absolute and relative peak power during the incremental test were assessed. Results After consuming the pre-exercise meal, both groups showed increased levels of RER, lactate and carbohydrate oxidation at rest and during the incremental test (p  0.8), and an improved V̇O2peak (p  0.5). Considering the previous 4-week nutritional intervention, carbohydrate metabolism was more upregulated (RERrest, RERexercise and ¸ carbohydrate oxidationexercise: p  0.8) in the LGI subgroup. Peak power during the final incremental test was slightly higher in the LGI subgroup compared with the HFLC subgroup (p = 0.365; Cohen’s d > 0.5). Conclusion In this group of male endurance athletes, a LGI diet seemed to result in more favourable performance metrics as compared to a HFLC diet despite increases in carbohydrate availability before undertaking the performance test likely due to the ability to sustain higher workloads in training. Trial registration DRKS00015521 and date of registration: 2018/09/13