Effects of Carbohydrates Versus Carbohydrates + Protein on Resistance Training Outcomes

Higher energy and carbohydrate intakes have been hypothesized to enhance resistance training adaptations, yet empirical evidence remains mixed. This study investigated whether supplemental carbohydrate-energy intake improves muscle hypertrophy, strength, and fatigue resistance in resistance-trained men.

Twenty resistance-trained men 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 diet. Primary outcomes included lean mass (dual-energy x-ray absorptiometry), muscle thickness and cross-sectional area (ultrasound), back squat one-repetition maximum, knee extensor peak torque, and fatigue index.

The carbohydrate-protein supplement produced significantly higher daily energy and carbohydrate intake compared to the protein-only supplement, with no differences in protein intake, fat intake, or training volume. No significant between-condition differences were observed for any outcome. These results suggest that modest increases in carbohydrate-energy intake outside of an energy deficit are unlikely to meaningfully enhance muscle hypertrophy, strength, or fatigue resistance in trained men.