Does eating more carbohydrate help you build more muscle?

Do You Need Lots of Carbs to Build Muscle? A Meta-Analysis of 11 Trials

2026-10-22 · By Anthony Falcone

Verdict: Drop it. Probably not on its own. Across 11 trials, eating more carbohydrate while protein stayed the same made no significant difference to muscle growth from strength training. The certainty is low, so a small benefit isn't ruled out, but total calories and protein matter more than the carb share.

What the researchers did

Gym advice often says you need plenty of carbohydrate to grow: carbs fuel harder sessions, refill muscle glycogen and raise insulin. This review asked a narrower question: if protein stays the same, does eating more carbohydrate lead to more muscle from strength training?

The authors searched MEDLINE, SPORTDiscus, SciELO and Google Scholar up to June 2025 for randomised trials in metabolically healthy adults aged 18–65. A trial counted if its groups differed in carbohydrate, by diet or by supplement, trained for at least 6 weeks and measured muscle size. Trials where protein or other supplements differed between groups were excluded, and so were measurements by tape or skinfold.

From 1,347 records, 11 trials qualified. They were small (20.6 participants on average) and short (8.5 weeks on average). Eight compared a ketogenic diet with a higher-carbohydrate one; the other three added carbohydrate as a snack or drink, two of them around training. Only two measured the muscle itself with ultrasound. The other nine estimated whole-body fat-free mass with DXA scans, body-fat scales or air-displacement pods.

What they found

Pooled together, the higher-carbohydrate groups did not gain significantly more muscle. The standardised effect size was 0.15 (95% confidence interval −0.10 to 0.40, p = 0.23), and the trials agreed with each other closely (no measurable heterogeneity). Dropping any single trial left the result non-significant, and there was no sign of publication bias.

The closer the analysis got to real muscle, the weaker any carb advantage looked. In the three trials judged to have matched calories, the effect was again 0.15 and not significant (p = 0.60). In the two ultrasound trials, it pointed the other way, slightly favouring less carbohydrate (−0.26), though two studies are too few to test.

Water is part of the story. Muscle stores carbohydrate as glycogen along with water, and body scans count that as fat-free mass. In one included trial, men who had followed a ketogenic diet for 10 weeks and then ate carbohydrate again for a week gained 4.8% fat-free mass in that week, which the authors say is likely refilled glycogen. So some of the "extra muscle" on high carbs may be water in the muscle, not new muscle tissue.

Calories muddied the picture in the other direction. Low-carb diets tend to blunt appetite, and in a follow-up analysis the lower-carb groups showed a non-significant trend towards losing more fat (effect size −0.23, p = 0.09). In one crossover trial, the high-carb phase worked out to roughly 5,337 kcal more energy over the study, by the authors' estimate from body composition changes. Even so, carbs didn't produce significantly more muscle.

How sure can we be?

The authors rated the certainty of the evidence as low (2 out of 4 on the GRADE scale), because the trials were small, the confidence interval crossed zero and risk of bias was moderate. Study quality was fair to good, averaging 9.8 out of 15. Their equivalence test suggests the true effect is either zero or small and positive; a moderate benefit looks unlikely, a small one can't be excluded.

Their practical conclusion: choose your carbohydrate intake on preference and other goals, as long as you eat enough total energy and protein. One caveat cuts the other way: because low-carb eating often lowers appetite, it can make it harder to stay in the calorie surplus that muscle gain usually needs.

What this means for you

For muscle growth, get total calories and protein right first; how much of the rest comes from carbohydrate seems to matter little.
Low-carb or keto while lifting didn't cost muscle growth in these trials, but watch your appetite: if you're trying to gain, a low-carb diet can quietly leave you short of calories.
Expect the scale and body-fat scales to move when you cut or add carbs. Much of that swing is glycogen and water, not muscle won or lost.
If you have diabetes, take medication that affects blood sugar, or have another medical condition, talk to your doctor before making a big change to your carbohydrate intake.

How much to trust it

The authors' own: the certainty of evidence is low; only two trials measured muscle directly; energy intake was poorly controlled in many trials; they didn't repeat their 2024 searches after registering the review (a 2025 update added no new trials); no formal framework (such as PICO) set the search terms, and the reference studies came from the authors' earlier work; and one database (SciELO) gave odd search results.
Most of the evidence is whole-body fat-free mass, which includes the glycogen and water that carbohydrate adds, so it can't cleanly separate muscle tissue from fluid.
Small, short trials: about 21 people and 8.5 weeks on average, mostly trained men, one trial in women only, and nobody over 65. Results over years, or in older adults, are untested.
Most comparisons were ketogenic versus normal diets, and the review lumped any difference in carbohydrate together. It can't tell you whether a specific intake, or carbs timed around training, makes a difference.
The authors expected a null result in advance, based on earlier studies that include their own 2022 review, and the risk-of-bias and GRADE ratings were added during peer review. No funding was received and the authors declare no directly relevant conflicts of interest.

The study

Henselmans M, Vårvik FT, Izquierdo M. The Effect of Carbohydrate Intake on Muscle Hypertrophy: A Systematic Review and Meta-analysis. Sports Medicine, 2026. doi.org/10.1007/s40279-025-02341-z

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