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

Area of Science:

• Sports Nutrition
• Exercise Physiology
• Muscle Metabolism

Background:

• High-carbohydrate diets are commonly advised for muscle hypertrophy.
• The specific impact of carbohydrate intake on muscle growth, separate from overall calories, requires further investigation.
• Previous analyses have not systematically evaluated carbohydrate's isolated effect outside ketogenic conditions.

Purpose of the Study:

• To meta-analyze the influence of higher carbohydrate intake on muscle hypertrophy.
• To assess carbohydrate's effect under isonitrogenous conditions (equal protein intake).

Main Methods:

• Systematic literature search across major databases (MEDLINE, SPORTDiscus, SciELO, Google Scholar) updated June 2025.
• Inclusion of randomized controlled trials comparing higher vs. lower carbohydrate intake during resistance training.
• Random-effects meta-analysis of standardized mean difference (SMD) scores, with heterogeneity and bias assessments (PRISMA, Cochrane RoB2, GRADE, TESTEX).

Main Results:

• Eleven studies included; pooled analysis showed no significant effect of carbohydrate intake on muscle hypertrophy (SMD = 0.15, p = 0.23).
• Negligible heterogeneity observed across studies.
• Subgroup analyses (isocaloric trials, direct imaging) also yielded non-significant results; GRADE certainty of evidence was low.

Conclusions:

• Higher carbohydrate intake may not independently promote muscle hypertrophy during resistance training.
• The certainty of this finding is low due to imprecision and moderate risk of bias.
• Future research should control energy intake strictly and use direct morphological measures to clarify carbohydrate's role.