The Effect of Carbohydrate Intake on Muscle Hypertrophy: A Systematic Review and Meta-analysis.

BACKGROUND

High-carbohydrate diets are often recommended to enhance resistance training-induced muscle hypertrophy; however, the isolated effect of carbohydrate intake on muscle growth has not been systematically analyzed outside ketogenic diet conditions.

OBJECTIVE

This meta-analysis aimed to assess whether a higher carbohydrate intake influences muscle hypertrophy under isonitrogenous conditions.

METHODS

A systematic search was conducted in the MEDLINE, SPORTDiscus, SciELO, and Google Scholar databases to identify randomized controlled trials comparing higher with lower carbohydrate intakes, whether via supplementation or diet, during resistance training in healthy adults with a measure of muscle size as an outcome. The search was last updated on 26 June, 2025. A random-effects model was used to meta-analyze standardized mean difference (SMD) scores according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Heterogeneity was assessed using χ2, T2, I2, and prediction intervals. Risk of bias was assessed using the Cochrane risk-of-bias (RoB2) tool. The certainty of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Study quality was assessed using the Assessment of Study Quality and Reporting in Exercise (TESTEX) scale.

RESULTS

Eleven studies met the inclusion criteria. A pooled analysis revealed no significant effect of carbohydrate intake on muscle hypertrophy (SMD = 0.15, p = 0.23), with negligible heterogeneity across studies. Sensitivity analyses confirmed the robustness of the findings, and no evidence of publication bias was detected. Subgroup analyses limited to isocaloric trials (SMD = 0.15, p = 0.60) and those employing direct imaging of muscle size (e.g., ultrasound) also yielded non-significant results (SMD =  - 0.26 based on only two studies). TESTEX study quality ranged from fair to good with an average score of 9.8 out of 15, but GRADE certainty of evidence was low (2/4) because of imprecision and a moderate risk of bias.

CONCLUSIONS

A higher carbohydrate intake may not independently enhance muscle hypertrophy during resistance training, though certainty of evidence is low. Future studies should employ stricter energy intake control and utilize direct morphological assessments to clarify the role of carbohydrate intake independent of total energy balance.

CLINICAL TRIAL REGISTRATION: PROSPERO CRD42024589461.