Are carbs good for muscle growth?

Extra carbohydrate does not build extra muscle once protein is in place. A 2026 meta-analysis of 11 randomized trials in healthy adults doing resistance training compared higher and lower carbohydrate intakes with protein matched, and found no significant effect on muscle growth, with a standardized difference of 0.15. The authors rated the certainty low. Cutting carbohydrate very hard, on a ketogenic diet, cost 1.1 to 2.8 lb (0.48 to 1.26 kg) of fat-free mass in two meta-analyses, while the larger of them found no measurable change in muscle mass or strength.

Unsettled. The main answer rests on small, short trials. The 11 trials averaged about 21 people and 8.5 weeks, and 9 of them measured fat-free mass rather than muscle. Fat-free mass includes water and glycogen, which shift when carbohydrate intake changes, so it can blur the result. Only two trials measured muscle size directly by ultrasound.

What the trials found

In the 2026 meta-analysis the trials disagreed very little with each other. The result held in the trials where calories were matched between groups, again with a standardized difference of 0.15 that was not significant. The two ultrasound trials together gave a difference of minus 0.26, which points slightly the other way.

A 2022 systematic review of 49 studies looked at strength instead of size. In 15 of 17 longer studies, carbohydrate intake made no difference to strength gains, one favored more carbohydrate and one favored less. The review suggests a possible benefit only for very high-volume workouts. It gives no pooled number.

Myth. A post-workout shake needs sugar to build muscle. In a crossover trial of 9 young men, adding 50 g of carbohydrate to 25 g of whey after leg exercise did not raise muscle protein synthesis or lower breakdown beyond whey alone. In 21 young adults, adding 30 g of sucrose to 10 g of essential amino acids did not improve the overall response either. Both trials measured a few hours, not months of training.

Carbohydrate with protein slows the protein down

In a randomized trial of 49 young and older men, taking 60 g of carbohydrate with 20 g of protein delayed the appearance of the dietary amino acids in the blood, and did not change muscle protein synthesis in either age group. That was a single meal without exercise.

In 27 older men, a carbohydrate drink raised myofibrillar protein synthesis about as much as whey or casein over three hours, with no significant difference between groups. The groups were small enough that a real difference in favor of protein could have been missed.

Months of training

In a 12-week trial of 68 untrained men, fat-free mass, muscle size and strength rose with training whether the post-workout drink was whey, carbohydrate or both, and the drinks were taken only two to three times a week. In an 8-week trial of 24 active men, 20 g of beef protein a day raised fat-free mass by 2.0% and whey by 1.4%, while 20 g of carbohydrate gave 0.0%, with an interval from minus 1.2 to 1.2%. The groups had 8 men each.

A 2026 crossover trial in 20 trained men added 50 g of carbohydrate a day to a 30 g protein supplement for 8 weeks. The carbohydrate phase supplied about 485 calories a day more, and lean mass, muscle size and strength did not differ between phases. Allocation was quasi-randomized, so we rate the trial lower, and it was too small to catch small effects.

Ketogenic diets

A 2022 meta-analysis of 13 randomized trials in 244 people doing resistance training found ketogenic diets lowered fat-free mass by 2.8 lb (1.26 kg) against non-ketogenic diets, with fat mass down 4.9 lb (2.21 kg). Energy intake was often not matched, and part of the fat-free loss is water and glycogen. A 2025 meta-analysis of 33 studies, some of them not randomized, found fat-free mass down 1.1 lb (0.48 kg) and no change in muscle mass, squat or bench press. A 2022 review of 5 studies in 111 resistance-trained people eating without planned calorie restriction found no difference in fat-free mass, and a 2024 meta-analysis found no loss of one-rep max squat or bench press in trained people on ketogenic diets.

Who should be careful

Not for everyone. Endurance athletes are the group with a stated risk. The International Society of Sports Nutrition warns that restricting carbohydrate can impair performance, particularly in endurance sports. If you train for endurance as well as size, that warning is the one to weigh. We have no card that puts a number on it.

If you are on a ketogenic diet while lifting, body composition readings may show some fat-free mass loss. The two meta-analyses above put it at 1.1 to 2.8 lb (0.48 to 1.26 kg), and part of it is water and glycogen rather than muscle.

If you add carbohydrate as sugary drinks or snacks, the World Health Organization recommends keeping free sugars below 10% of total energy for adults and children. That limit is based on body weight and tooth decay, not on muscle.

We have no cards on carbohydrate and muscle in people with diabetes, kidney disease or in pregnancy, so this page says nothing about them.

What expert bodies say

The International Society of Sports Nutrition, in its 2017 position stand on diets and body composition, states that a wide range of approaches, from low-fat to low-carbohydrate or ketogenic, can be similarly effective for improving body composition. A position stand is an expert reading of the evidence, not a pooled analysis.

The joint 2016 position of the American College of Sports Medicine and dietitian bodies on nutrition and athletic performance could not be read in full, and we hold no card from it.

How we searched

What would change this answer

• Larger trials with calories matched that measure muscle directly by MRI or ultrasound. Fat-free mass moves with water and glycogen, and only two of the 11 pooled trials measured muscle itself.
• The registered trial NCT07600138, comparing carbohydrate with carbohydrate plus protein during resistance training.
• Trials longer than a few months. The pooled trials averaged 8.5 weeks.

Sources

1. ev-cbmg-01 · Meta-analysis or systematic review · systematic review and random-effects meta-analysis of RCTs with RoB2 and GRADE · n = 11 RCTs
   A pooled analysis revealed no significant effect of carbohydrate intake on muscle hypertrophy (SMD = 0.15, p = 0.23), with negligible heterogeneity across studies.
   
   Who: healthy adults in RCTs comparing higher vs lower carbohydrate intake (diet or supplement) during resistance training, isonitrogenous, searched to June 2025
   Effect: muscle hypertrophy SMD 0.15 (p = 0.23), negligible heterogeneity; isocaloric trials SMD 0.15 (p = 0.60); direct imaging SMD -0.26 (2 studies); GRADE certainty low
   Certainty: Low certainty due to imprecision and moderate risk of bias; PROSPERO CRD42024589461.
   Sports Med, 2026 · checked 2026-10-07 · we read the abstract
2. ev-cbmg-02 · Meta-analysis or systematic review · study characteristics within a systematic review and meta-analysis · n = 11 RCTs
   Only two studies, Santos et al. [43] and Wilson et al. [32], used direct assessments of muscle size via ultrasound; the remaining studies relied on whole-body FFM as a proxy for muscle hypertrophy.
   
   Who: 11 RCTs of carbohydrate intake and resistance training, mostly trained men
   Effect: mean sample 20.6 participants, mean duration 8.5 weeks; 9 of 11 used whole-body fat-free mass as a proxy for hypertrophy
   Certainty: Fat-free mass includes water and glycogen, so carbohydrate changes can distort it.
   Sports Med, 2026 · checked 2026-10-07 · we read the fulltext
3. ev-cbmg-03 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 244
   The pooled results demonstrated that KDs significantly decreased BM [(WMD = -3.67 kg; 95% CI: -4.44, -2.90, p < 0.001)], FM [(WMD = -2.21 kg; 95% CI: -3.09, -1.34, p < 0.001)], FFM [(WMD = -1.26 kg; 95% CI: -1.82, -0.70, p < 0.001)], BMI [(WMD = -1.37 kg.m-2; 95% CI: -2.14, -0.59, p = 0.022)], and BFP [(WMD = -2.27%; 95% CI: -3.63, -0.90, p = 0.001)] compared to non-KDs.
   
   Who: individuals performing resistance training in RCTs of ketogenic vs non-ketogenic diets, searched to February 2021
   Effect: fat-free mass WMD -2.8 lb (95% CI -4 to -1.5; metric: -1.26 kg, -1.82 to -0.70); fat mass -4.9 lb (-2.21 kg); body mass -8.1 lb (-3.67 kg)
   Certainty: Fat-free mass loss partly reflects water and glycogen; energy intake often not matched.
   Crit Rev Food Sci Nutr, 2022 · checked 2026-10-07 · we read the abstract
4. ev-cbmg-04 · Meta-analysis or systematic review · systematic review and meta-analysis with GRADE · n = 33 studies
   However, a significant decrease in fat-free mass (WMD: -0.48, 95%CI: -0.73 to -0.23, p < 0.001) and fat mass (WMD: -1.31, 95%CI: -2.06 to -0.57, p < 0.001) was observed in the KD group compared with the control group.
   
   Who: adults in randomized and non-randomized controlled studies comparing ketogenic with other diets, searched to July 2025
   Effect: muscle mass WMD 0.06 (95% CI -1.97 to 2.09, NS); squat SMD -0.19 (NS); bench press SMD -0.15 (NS); fat-free mass WMD -1.1 lb (-1.6 to -0.51; metric: -0.48 kg, -0.73 to -0.23)
   Certainty: Includes non-randomized controlled studies; mixed athletic and non-athletic samples.
   J Health Popul Nutr, 2025 · checked 2026-10-07 · we read the abstract
5. ev-cbmg-05 · Meta-analysis or systematic review · systematic review and meta-analysis · n = 111
   We found no significant differences between groups in the FFM variables, and more research is needed to perform studies with similar ketogenic diets and control diet interventions.
   
   Who: athletes or resistance-trained participants (87 male, 24 female) on ketogenic diets without programmed energy restriction
   Effect: no significant between-group difference in fat-free mass
   Certainty: Only five small studies; authors note poor adherence beyond eight weeks.
   Int J Environ Res Public Health, 2022 · checked 2026-10-07 · we read the abstract
6. ev-cbmg-06 · Meta-analysis or systematic review · systematic review and meta-analysis · n = 119
   We did not find significant differences between the groups in the variables of SQ or BP, although the size of the effect was slightly higher in the ketogenic group.
   
   Who: resistance-trained participants or athletes; 106 in squat and 119 in bench press analyses
   Effect: no significant difference in 1-RM squat or bench press between ketogenic and control groups
   Certainty: Strength, not muscle size; small pooled samples.
   Nutrients, 2024 · checked 2026-10-07 · we read the abstract
7. ev-cbmg-07 · Meta-analysis or systematic review · systematic review of trials manipulating carbohydrate intake · n = 49 studies
   Longer-term changes in performance were not influenced by carbohydrate intake in 15 studies; one study favored the higher- and one the lower-carbohydrate condition.
   
   Who: strength trainees or athletes (39 studies), recreationally active (6) or untrained (4)
   Effect: long-term: no influence in 15 studies, one favored higher and one lower carbohydrate; acute: no benefit in 13 of 19 studies
   Certainty: No pooled estimate; outcome is strength performance, not muscle size.
   Nutrients, 2022 · checked 2026-10-07 · we read the abstract
8. ev-cbmg-08 · Randomized controlled trial(s) · randomized crossover trial with stable isotopes and muscle biopsies · n = 9
   The concurrent ingestion of 50 g of CHO with 25 g of protein did not stimulate mixed MPS or inhibit MPB more than 25 g of protein alone either at rest or after resistance exercise.
   
   Who: young men performing unilateral knee extension; 25 g whey vs 25 g whey plus 50 g maltodextrin
   Effect: insulin AUC 5-fold higher with carbohydrate; no difference in muscle protein synthesis or breakdown at rest or after exercise
   Certainty: Acute measurement over hours; tiny sample.
   Med Sci Sports Exerc, 2011 · checked 2026-10-07 · we read the abstract
9. ev-cbmg-09 · Randomized controlled trial(s) · randomized trial with intrinsically labeled protein and tracer infusion · n = 49
   Carbohydrate coingestion with protein delays dietary protein digestion and absorption but does not modulate postprandial muscle protein accretion in healthy young or older men.
   
   Who: healthy young (21 years) and older (75 years) men; 20 g labeled protein with or without 60 g carbohydrate
   Effect: delayed appearance of dietary amino acids (P = .001); no change in postprandial muscle protein synthesis in either age group
   Certainty: Single meal, no exercise; acute outcome.
   J Clin Endocrinol Metab, 2014 · checked 2026-10-07 · we read the abstract
10. ev-cbmg-10 · Randomized controlled trial(s) · randomized trial with stable isotopes and muscle biopsies · n = 21
    Because the overall muscle protein anabolic response was not improved in either the EAA+ALA or EAA+CHO group compared with EAA, we conclude that protein nutritional interventions to enhance muscle protein anabolism do not require such additional energy.
    
    Who: young men and women; 10 g EAA alone, with 30 g sucrose, or with 30 g alanine
    Effect: similar areas under the curve for fractional synthetic rate, synthesis, breakdown and net balance across groups
    Certainty: Acute, resting state.
    J Nutr, 2013 · checked 2026-10-07 · we read the abstract
11. ev-cbmg-11 · Observational data · quasi-randomized double-blind counterbalanced crossover trial · n = 20
    No significant differences between conditions were observed for any outcome, including in the sensitivity analyses.
    
    Who: resistance-trained men, 9.7 years training; 30 g protein with 4 g vs 54 g carbohydrate daily, 8 weeks each
    Effect: +485 calories/day and +33 g carbohydrate/day in the carbohydrate phase; no significant difference in DXA lean mass, ultrasound muscle size, squat 1RM or torque
    Certainty: Quasi-randomized, so rated C; underpowered for small effects.
    Nutrients, 2026 · checked 2026-10-07 · we read the abstract
12. ev-cbmg-12 · Randomized controlled trial(s) · randomized controlled trial, 12 weeks · n = 68
    Twelve-week RT led to increased fat-free mass, muscle size and strength independent of post-exercise nutrient intake (P < 0.05).
    
    Who: previously untrained males; 30 g whey (n = 22), isocaloric maltodextrin (n = 21) or both (n = 25) after training
    Effect: fat-free mass, muscle size and strength increased independent of drink (P < 0.05)
    Certainty: Drinks only 2 to 3 times a week.
    J Int Soc Sports Nutr, 2015 · checked 2026-10-07 · we read the abstract
13. ev-cbmg-13 · Randomized controlled trial(s) · randomized controlled trial, 8 weeks · n = 24
    Beef (2.0%, CI, 0.2-2.38%) and Whey (1.4%, CI, 0.2-2.6%) but not Carbohydrate (0.0%, CI, -1.2-1.2%) increased fat-free mass.
    
    Who: recreationally active males doing resistance training; 20 g beef protein, whey or carbohydrate daily (n = 8 each)
    Effect: fat-free mass: beef +2.0%, whey +1.4%, carbohydrate 0.0% (95% CI -1.2 to 1.2); vastus medialis thickness rose in all groups, carbohydrate +6.3%
    Certainty: Very small groups; supplement mixed with orange juice in all arms.
    Int J Sport Nutr Exerc Metab, 2017 · checked 2026-10-07 · we read the abstract
14. ev-cbmg-14 · Randomized controlled trial(s) · randomized trial with stable isotopes, unilateral exercise model · n = 27
    Milk protein and carbohydrate supplementation stimulate myofibrillar protein synthesis in older men, with no further effect of heavy resistance exercise within 0-3 h post exercise.
    
    Who: older men (69 years); 0.45 g/kg lean mass of whey hydrolysate, caseinate or carbohydrate; one leg exercised
    Effect: fed-rest FSR 0.043 (whey), 0.045 (casein), 0.035 (carbohydrate) %/h vs basal about 0.03; no significant group differences
    Certainty: Acute 3-hour window; small groups may miss a real difference favoring protein.
    Eur J Nutr, 2019 · checked 2026-10-07 · we read the abstract
15. ev-cbmg-15 · Position of an expert body · society position stand (narrative review) · n = —
    A wide range of dietary approaches (low-fat to low-carbohydrate/ketogenic, and all points between) can be similarly effective for improving body composition, and this allows flexibility with program design.
    
    Who: athletes and general population seeking body composition change
    Effect: no single macronutrient pattern preferred for body composition
    Certainty: Expert position, not a pooled analysis.
    Journal of the International Society of Sports Nutrition, 2017, 14:16 (Aragon et al., ISSN position stand: diets and body composition) · checked 2026-10-07 · we read the fulltext
16. ev-cbmg-16 · Position of an expert body · society position stand (narrative review) · n = —
    Carbohydrate restriction can have an ergolytic potential, particularly for endurance sports.
    
    Who: athletes, particularly endurance athletes
    Effect: carbohydrate restriction potentially ergolytic, particularly for endurance
    Certainty: Qualitative statement.
    Journal of the International Society of Sports Nutrition, 2017, 14:16 (Aragon et al., ISSN position stand: diets and body composition) · checked 2026-10-07 · we read the fulltext
17. ev-cbmg-17 · Position of an expert body · WHO guideline (NUGAG, GRADE) · n = —
    In both adults and children, WHO recommends reducing the intake of free sugars to less than 10% of total energy intake2 (strong recommendation).
    
    Who: adults and children
    Effect: free sugars under 10% of energy (strong recommendation); further reduction below 5% suggested
    Certainty: Based on body weight and dental caries, not muscle outcomes.
    WHO, 2015, Guideline: sugars intake for adults and children · checked 2026-10-07 · we read the section