Effects of Modest Carbohydrate–Energy Supplementation on Resistance Training Adaptations in Trained Men: A Crossover Trial

Background/Objectives: Higher energy and carbohydrate intakes have been hypothesized to enhance resistance training adaptations, yet empirical evidence remains mixed. The purpose of this study was to investigate whether supplemental carbohydrate–energy intake improves muscle hypertrophy and strength. Methods: Twenty resistance-trained men (26.7 ± 4.9 years old, 9.7 ± 6.1 years training experience) completed a quasi-randomized, double-blinded, counterbalanced crossover trial. Participants consumed either a daily protein-only supplement (30 g protein, 4 g carbohydrate) or a daily protein-plus-carbohydrate supplement (30 g protein, 54 g carbohydrate) for 8 weeks each, followed by crossover, while continuing their habitual training and nutrition. Primary outcomes included lean mass obtained using dual-energy X-ray absorptiometry, muscle thickness and cross-sectional area obtained via ultrasound, back squat one-repetition maximum, fatigue index, and knee extensor peak torque. Differences in estimated marginal means, controlling for order and phase effects, were analyzed via linear mixed models, with first-phase-only ANCOVAs as sensitivity analyses. Results: The carbohydrate–protein condition resulted in significantly higher daily energy (+485 kcal/d; p = 0.017) and carbohydrate intake (+33 g/d; p = 0.043) than the protein-only condition, with no differences in protein or fat intake or training volume. No significant differences between conditions were observed for any outcome, including in the sensitivity analyses. Conclusions: Modest supplemental carbohydrate–energy intake did not significantly augment muscle hypertrophy, fatigue resistance or strength in trained men within our study context. More high-powered research is needed to determine how much and under which circumstances carbohydrate–energy intake affects resistance training adaptations.