Does eating more protein help you build muscle?

Yes, by a small amount, and only alongside resistance training. Across 49 randomized trials in 1863 adults who trained for at least six weeks, protein supplements added 0.66 lb (0.30 kg) of fat-free mass and 5.5 lb (2.49 kg) to a one-repetition maximum. Past a total of about 1.62 g of protein per kg of body weight a day, extra protein added nothing more. Most of the gain sat in people who already lifted.

Established. Protein on top of resistance training builds slightly more lean mass than training alone. Three meta-analyses of randomized trials agree on the direction. The size is a few hundred grams over weeks to months, with 0.66 lb (0.30 kg) in the largest pooling of 49 trials.

What the trials found

The main synthesis, Morton 2018, pooled 49 trials in 1863 healthy adults doing resistance training for six weeks or more. Fat-free mass rose 0.66 lb (0.30 kg) more with protein, with a confidence interval from 0.2 to 1.1 lb (0.09 to 0.52 kg). One-repetition maximum strength rose 5.5 lb (2.49 kg) more, with an interval from 1.4 to 9.5 lb (0.64 to 4.33 kg). The same analysis found a breakpoint near 1.62 g per kg a day of total protein, beyond which fat-free mass stopped climbing. The authors give that breakpoint wide uncertainty. It marks where gains level off and says nothing about safety.

The split by training history matters more than the headline. In people already used to lifting, the gain was 2.3 lb (1.05 kg), from 1.3 to 3.3 lb (0.61 to 1.50 kg). In untrained people it was 0.33 lb (0.15 kg), with an interval from minus 0.04 to 0.68 lb (0.02 to 0.31 kg) that did not reach significance. Only 10 of the trials were in trained people, and the abstract adds that the effect shrank by about 0.02 lb (0.01 kg) with each year of age.

Two other meta-analyses land in the same place. An earlier one of 22 trials in 680 younger and older people found 1.5 lb (0.69 kg) more fat-free mass and 30 lb (13.5 kg) more on the leg press. It was smaller and older, which likely explains the larger number. A pooling of 65 trials in 2907 people found lean body mass rose 1.4 lb (0.62 kg) in adults aged 18 to 121 and 1 lb (55 and 0.46 kg) in those over 55. In that review handgrip and leg press strength did not change significantly, and the timing of the protein made no difference.

Not every review agrees on muscle. In 12 trials of 261 adults aged 18 to 30, whey or soy during training did not change lean body mass, although whey improved bench press and squat performance, by mean differences of 8.87 and 9.60 in the review's own units. These were small studies. They disagree with Morton 2018 on mass and agree with it on strength.

Older adults

In older adults who lift, 21 trials in 1249 people found protein added 0.51 lb (0.23 kg) of fat-free mass and 0.86 lb (0.39 kg) of appendicular muscle, with small gains in grip and leg strength and no significant change in muscle function. An earlier review of 9 trials in 462 people with a mean age of 61 to 79 found a gain in fat-free mass, a standardized difference of 0.23, while muscle mass and strength did not change significantly. That review rated its own included studies as low quality.

In 13 trials of 1057 adults over 65 with sarcopenia or frailty, protein plus exercise raised the skeletal muscle index by 0.89 kg/m2 and grip by 5.8 lb (2.64 kg) over exercise alone. The authors rated this evidence as very low quality.

Myth. Protein alone, without exercise, has not been shown to build muscle in older adults. Across 6 randomized trials in physically inactive older people, protein supplements made no statistically significant difference to total lean body mass. The abstract does not give the total number of people.

Two recent trials that found nothing extra

In a 12-week trial of 295 frail older adults on supervised resistance training, mean age 73.9, adding whey and diet advice to reach 1.2 to 1.5 g per kg did not produce larger gains in leg press strength, appendicular lean mass or performance. In an exploratory analysis, the authors report a strength gain of 14 lb (6.4 kg) in the subgroup eating under 1.2 g per kg at the start. In a 12-week trial of 108 women aged 40 to 77 on supervised training, targets of 0.8, 1.6 or 2.2 g per kg made no detectable difference to skeletal muscle mass. Muscle there was measured by bioimpedance in 83 analyzed women, and the authors say plainly that a null result does not mean the doses are equal.

Plant or animal protein

Across 30 trials, plant protein built slightly less muscle than animal protein, a standardized difference of minus 0.20, with the gap in adults under 60. Soy matched milk protein, at minus 0.02. Rice, chia, oat and potato protein came out further behind, at minus 0.58, from only 5 trials. These are standardized differences and cannot be read as kilograms.

Mixing protein with creatine or vitamin D does not beat plain protein. Across 35 trials in 1387 people, multi-ingredient supplements added 1.8 lb (0.80 kg) of fat-free mass against all comparison groups, but that comparison pools placebo with protein-only arms, and against protein alone they showed no advantage.

Who should be careful

For healthy kidneys, the trials are reassuring over the short term. In 28 trials with 1358 adults without kidney disease, high-protein diets of at least 1.5 g per kg a day did not change kidney filtration rate over time compared with normal or lower protein. Those trials were short, and the risk of selection bias was unclear. A 2026 meta-analysis of 22 trials found high-protein diets raised eGFR without a change in serum creatinine across 19 trials in 1044 adults. The rise in eGFR may be an adaptation of blood flow, and the authors call the long-term kidney effects uncertain.

Not for everyone. People with severe kidney disease who are not on dialysis are the exception. The PROT-AGE expert group says older people with an estimated GFR below 30 may need to limit protein. If that is you, the right intake is a decision for the clinician treating your kidneys.

What expert bodies say

The International Society of Sports Nutrition says 1.4 to 2.0 g of protein per kg a day is enough for most exercising people to build and keep muscle. That is a position of a scientific society, and it sits close to the 1.62 g breakpoint in Morton 2018. A small study of 8 resistance-trained women measured after one workout put their requirement at about 1.49 to 1.53 g per kg a day, which is one session and a short recovery window. The PROT-AGE group advises people over 65 to eat at least 1.0 to 1.2 g per kg a day, and 1.2 or more if they are active.

How we searched

What would change this answer

• Larger and longer randomized trials in untrained and older people at fixed targets in grams per kilogram. The current split between trained and untrained lifters rests on only 10 trials in the trained group.
• Kidney outcomes measured over years in people eating above 2 g per kg a day. The kidney trials we have are short and in people with healthy kidneys.
• Trials in older adults with several chronic diseases. A review looking for them found none that analyzed protein intake.

For protein in food, see the whey page and the protein guide.

Sources

1. ev-protmus-01 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 1863
   Data from 49 studies with 1863 participants showed that dietary protein supplementation significantly (all p<0.05) increased changes (means (95% CI)) in: strength-one-repetition-maximum (2.49 kg (0.64, 4.33)), FFM (0.30 kg (0.09, 0.52))
   
   Who: Healthy adults in 49 RCTs of resistance training of 6 weeks or more
   Effect: Fat-free mass +0.66 lb (95% CI 0.2 to 1.1; metric: 0.30 kg, 0.09 to 0.52); 1RM strength +5.5 lb (95% CI 1.4 to 9.5; metric: 2.49 kg, 0.64 to 4.33)
   Certainty: Main synthesis; the effect is small in kg but stable. Without training it is not included here.
   Br J Sports Med, 2018 · checked 2026-10-06 · we read the abstract
2. ev-protmus-02 · Meta-analysis or systematic review · meta-regression with two-phase breakpoint analysis · n = 1863
   Protein supplementation beyond total protein intakes of 1.62 g/kg/day resulted in no further RET-induced gains in FFM.
   
   Who: Healthy adults in RCTs of resistance training
   Effect: Breakpoint about 1.62 g/kg/day for fat-free mass gains
   Certainty: The breakpoint has wide uncertainty; this is not a safety ceiling.
   Br J Sports Med, 2018 · checked 2026-10-06 · we read the abstract
3. ev-protmus-03 · Meta-analysis or systematic review · subgroup analysis within meta-analysis of RCTs · n = 1863
   untrained: 0.15 kg (−0.02, 0.31), p=0.08 and trained: 1.05 kg (0.61, 1.50), p<0.0001.
   
   Who: Untrained and resistance-trained adults in RCTs of resistance training
   Effect: Trained +2.3 lb (1.3 to 3.3; metric: 1.05 kg, 0.61 to 1.50); untrained +0.33 lb (-0.04 to 0.68; metric: 0.15 kg, -0.02 to 0.31)
   Certainty: Subgroup; there are only 10 trained studies. The abstract adds: the effect weakens with age (-0.01 kg per year).
   Br J Sports Med, 2018 · checked 2026-10-06 · we read the fulltext
4. ev-protmus-04 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 680
   Protein supplementation showed a positive effect for FFM (weighted mean difference: 0.69 kg; 95% CI: 0.47, 0.91 kg; P < 0.00001) and 1-RM leg press strength (weighted mean difference: 13.5 kg; 95% CI: 6.4, 20.7 kg; P < 0.005) compared with a placebo after prolonged resistance-type exercise training in younger and older subjects.
   
   Who: Younger and older subjects in 22 RCTs of resistance training over 6 weeks
   Effect: Fat-free mass +1.5 lb (95% CI 1 to 2; metric: 0.69 kg, 0.47 to 0.91); 1RM leg press +30 lb (95% CI 14 to 46; metric: 13.5 kg, 6.4 to 20.7)
   Certainty: Older and smaller synthesis; larger effect than in Morton 2018, probably because of fewer studies.
   Am J Clin Nutr, 2012 · checked 2026-10-06 · we read the abstract
5. ev-protmus-05 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 2907
   The protein supplementation was effective in improving (mean difference; 95% CI) LBM in adults (0.62 kg; 0.36, 0.88) and older adults (0.46 kg; 0.23, 0.70), but not handgrip strength (older adults: 0.26 kg; -0.51, 1.04) and leg press strength (adults: 5.80 kg; -0.33, 11.93; older adults: 1.97 kg; -2.78, 6.72).
   
   Who: Healthy adults (18 to 55 years) and older adults (over 55 years) in 65 RCTs
   Effect: Lean body mass +1.4 lb (0.79 to 1.9; metric: 0.62 kg, 0.36 to 0.88) adults; +1 lb (0.51 to 1.5; metric: 0.46 kg, 0.23 to 0.70) older adults; handgrip and leg press not significant
   Certainty: Strength did not increase significantly; timing does not matter by subgroups.
   J Nutr, 2020 · checked 2026-10-06 · we read the abstract
6. ev-protmus-06 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 1057
   Combined protein and exercise interventions demonstrated significant improvements in skeletal muscle index (MD = 0.89 kg/m², 95 % CI: 0.45 to 1.33) and handgrip strength (MD: +2.64 kg, 95 % CI: +0.75 to +4.53) compared to exercise alone.
   
   Who: Adults aged 65 or over with sarcopenia or physical frailty, 13 RCTs
   Effect: Skeletal muscle index +0.89 kg/m2 (0.45 to 1.33); handgrip +5.8 lb (1.7 to 10; metric: 2.64 kg, 0.75 to 4.53) versus exercise alone
   Certainty: The authors rated the quality of evidence as very low.
   Arch Gerontol Geriatr, 2025 · checked 2026-10-06 · we read the abstract
7. ev-protmus-07 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = —
   Protein supplementation had no statistically significant effect on total lean body mass (p> 0.05).
   
   Who: Physically inactive older adults, 6 RCTs (8 data groups)
   Effect: No significant effect on total lean body mass (p > 0.05)
   Certainty: Few studies; total N not named in the abstract.
   BMC Geriatr, 2025 · checked 2026-10-06 · we read the abstract
8. ev-protmus-08 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 261
   The analysis found no significant effect of either whey or soy protein supplementation on LBM. However, protein supplement increased peak plasma total EAA with whey protein significantly improved bench press (mean difference [MD] 8.87; 95% CI: 5.95-11.79) and squat performance (MD 9.60; 95% CI: 5.61-13.60), with low to no heterogeneity.
   
   Who: Young adults aged 18 to 30 doing resistance training, 12 RCTs
   Effect: Lean body mass not changed; bench press MD 8.87 (5.95 to 11.79), squat MD 9.60 (5.61 to 13.60) with whey; units not stated in the abstract
   Certainty: Small studies; diverges from Morton 2018 on mass, agrees on strength.
   J Diet Suppl, 2026 · checked 2026-10-06 · we read the abstract
9. ev-protmus-09 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = —
   Compared with animal protein, plant protein resulted in lower muscle mass following the intervention (SMD = -0.20; 95% CI: -0.37, -0.03; P = .02), with stronger effects in younger (<60 years; SMD = -0.20; 95% CI: -0.37, -0.03; P = .02) than in older (≥60 years; SMD = -0.05; 95% CI: -0.32, 0.23; P = .74) adults.
   
   Who: Adults in 30 RCTs comparing plant with animal protein
   Effect: SMD -0.20 (95% CI -0.37 to -0.03); soy versus milk SMD -0.02 (-0.20 to 0.16)
   Certainty: SMD, not kilograms; the difference from non-diverse plant proteins (rice, oats, potato) is larger.
   Nutr Rev, 2025 · checked 2026-10-06 · we read the abstract
10. ev-protmus-10 · Randomized controlled trial(s) · secondary analysis of a randomized controlled trial · n = 295
    Overall, the protein intervention did not result in significantly greater gains in leg press muscle strength, appendicular lean mass, or physical performance compared to PRT-only (p > 0.05).
    
    Who: 295 frail community-dwelling older adults, mean age 73.9, 69% women, 12 weeks
    Effect: No significant difference in leg press 1RM, appendicular lean mass or performance; protein intake +0.4 g/kg (0.3 to 0.5)
    Certainty: Exploratory: strength benefit in those who ate less than 1.2 g/kg at baseline (+14 lb (6.4 kg)).
    J Nutr Health Aging, 2026 · checked 2026-10-06 · we read the abstract
11. ev-protmus-11 · Randomized controlled trial(s) · randomized 2 x 3 factorial trial · n = 108
    For SMM, no training-condition × protein-target interaction (p = 0.856), marginal protein-target effect (p = 0.726), or marginal training-condition effect (p = 0.273) was detected.
    
    Who: 108 women aged 40 to 77, 12 weeks of resistance or concurrent training
    Effect: No marginal protein-target effect on skeletal muscle mass (p = 0.726)
    Certainty: Mass by bioimpedance; analysis of 83 people; the authors state directly that null does not mean equality of doses.
    J Int Soc Sports Nutr, 2026 · checked 2026-10-06 · we read the abstract
12. ev-protmus-12 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 1358
    The change in GFR did not differ between interventions (SMD: 0.11; 95% CI: -0.05, 0.27; P = 0.16).
    
    Who: Adults without kidney disease in 28 RCTs, more than 4 days
    Effect: Change in GFR SMD 0.11 (95% CI -0.05 to 0.27), not significant
    Certainty: Healthy kidneys only; risk of selection bias unclear; short studies.
    J Nutr, 2018 · checked 2026-10-06 · we read the abstract
13. ev-protmus-13 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 1044
    High-protein diets did not significantly change serum creatinine (19 trials; n = 1044; standardised mean difference 0.08, 95% confidence interval -0.09 to 0.25; I 2 = 20.8%), without consistent biochemical evidence suggestive of renal injury.
    
    Who: Adults without chronic kidney disease, 22 RCTs (creatinine: 19 trials, 1044 people)
    Effect: eGFR SMD 0.39 (0.09 to 0.69); serum creatinine SMD 0.08 (-0.09 to 0.25); fat-free mass not significantly changed
    Certainty: The eGFR increase may be a hemodynamic adaptation; no long-term data.
    Diabetes Obes Metab, 2026 · checked 2026-10-06 · we read the abstract
14. ev-protmus-14 · Position of an expert body · consensus position paper · n = —
    Older people with severe kidney disease (ie, estimated GFR <30 mL/min/1.73 m(2)), but who are not on dialysis, are an exception to this rule; these individuals may need to limit protein intake.
    
    Who: Older people over 65; exception for eGFR below 30 mL/min/1.73 m2 not on dialysis
    Effect: At least 1.0 to 1.2 g/kg/day; 1.2 or more if active; limit with eGFR below 30
    Certainty: Position of the EUGMS expert group, not its own analysis.
    J Am Med Dir Assoc, 2013 · checked 2026-10-06 · we read the abstract
15. ev-protmus-15 · Position of an expert body · position stand · n = —
    For building muscle mass and for maintaining muscle mass through a positive muscle protein balance, an overall daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day (g/kg/d) is sufficient for most exercising individuals
    
    Who: Exercising individuals
    Effect: 1.4 to 2.0 g/kg/day
    Certainty: Scientific society position (T3 context), not its own meta-analysis; matches the Morton 2018 breakpoint.
    Jager R et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr, 2017 · checked 2026-10-06 · we read the fulltext
16. prot-t5 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized trials · n = 17 and 5 trials
    There was no pooled effect difference between soy and milk protein for muscle mass (SMD = -0.02; 95% CI: -0.20, 0.16; P = .80) (n = 17 RCTs), yet animal protein improved muscle mass compared with non-soy plant proteins (rice, chia, oat, and potato; SMD = -0.58; 95% CI: -1.06, -0.09; P = .02) (n = 5 RCTs)
    
    Who: adults, 17 trials for the soy comparison and 5 for non-soy plant proteins
    Effect: soy against milk protein standardized mean difference -0.02 (95% CI -0.20 to 0.16); animal against non-soy plant proteins -0.58 (-1.06 to -0.09)
    Certainty: small numbers of trials for the non-soy comparison
    Robinson-Mitchell et al., Nutrition Reviews, 2025 · checked 2026-09-16 · we read the abstract
17. prot-t9 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials with resistance training of six weeks or longer · n = 1,387 participants
    Data from 35 trials with 1387 participants showed significant (p<0.05) increases in FFM (0.80 kg (95% CI 0.44 to 1.15)), 1RM lower body (4.22 kg (95% CI 0.79 to 7.64)) and 1RM upper body (2.56 kg (95% CI 0.79 to 4.33)) where a supplement was compared with all non-MIP supplemented conditions (means (95% CI)).
    
    Who: healthy adults in 35 trials; the commonest combinations were protein with creatine (17 trials) and protein with vitamin D (10 trials)
    Effect: against all non-multi-ingredient conditions: fat-free mass +1.8 lb (95% CI 0.97 to 2.5; metric: 0.80 kg, 0.44 to 1.15), lower-body one-rep max +9.3 lb (95% CI 1.7 to 17; metric: 4.22 kg, 0.79 to 7.64), upper-body one-rep max +5.6 lb (95% CI 1.7 to 9.5; metric: 2.56 kg, 0.79 to 4.33); no advantage over protein alone
    Certainty: the comparison group pools placebo and protein-only arms, so the headline number is not a protein-versus-creatine contrast
    O'Bryan et al., British Journal of Sports Medicine, 2020 · checked 2026-09-17 · we read the abstract
18. prot-t10 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials of protein supplementation combined with resistance training · n = 1,249 participants
    Twenty-one RCTs were included, involving 1,249 participants. The results showed that protein supplementation combine with RT significantly enhances the muscle mass and strength of the older adults, where FFM (fat-free mass) increased by 0.23 kg (95% CI: 0.09, 0.38; P=0.002), ASMM (appendicular skeletal muscle mass) by 0.39 kg (95% CI: 0.14, 0.64; P=0.002), handgrip strength by 0.29 kg (95% CI: 0.08, 0.50; P=0.008), knee extension strength by 0.27 kg (95% CI: 0.06, 0.47; P=0.013), leg press strength by 0.33 kg (95% CI: 0.01, 0.64; P=0.04), but no significant effects were seen on muscle function.
    
    Who: older adults in 21 randomized trials published before May 2018
    Effect: fat-free mass +0.51 lb (95% CI 0.2 to 0.84; metric: 0.23 kg, 0.09 to 0.38), appendicular skeletal muscle mass +0.86 lb (95% CI 0.31 to 1.4; metric: 0.39 kg, 0.14 to 0.64), handgrip +0.64 lb (95% CI 0.18 to 1.1; metric: 0.29 kg, 0.08 to 0.50), knee extension +0.6 lb (95% CI 0.13 to 1; metric: 0.27 kg, 0.06 to 0.47), leg press +0.73 lb (95% CI 0.02 to 1.4; metric: 0.33 kg, 0.01 to 0.64); no significant effect on muscle function
    Certainty: strength gains are reported in kilograms but pooled across very different tests; the split between mass and function is the point, not the exact size
    Liao et al., Journal of Nutrition, Health and Aging, 2019 · checked 2026-09-17 · we read the abstract
19. prot-t11 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials with resistance training of six weeks or longer · n = 462 participants
    Overall, protein supplementation in combination with resistance training was associated with gains in fat-free mass, resulting in a standardized mean difference (SMD) of 0.23 [95% confidence interval (CI), 0.05-0.42]. However, protein supplementation was not associated with changes in muscle mass (0.14, 95% CI -0.05 to 0.32) or muscle strength (0.13, 95% CI -0.06 to 0.32).
    
    Who: adults with a mean age of 61 to 79 years in 9 randomized trials
    Effect: fat-free mass standardized mean difference 0.23 (95% CI 0.05 to 0.42); muscle mass 0.14 (95% CI -0.05 to 0.32) and muscle strength 0.13 (95% CI -0.06 to 0.32), both crossing no effect
    Certainty: the review itself rates the general quality of included studies as low, with widely varying protein doses and sources
    Finger et al., Sports Medicine, 2015 · checked 2026-09-17 · we read the abstract
20. prot-r2-5 · Randomized controlled trial(s) · controlled metabolic study using the indicator amino acid oxidation technique with randomized test protein intakes and biphase linear regression · n = 8 women
    A mixed model biphase linear regression revealed a break point (i.e., estimated average requirement) of 1.49 ± 0.44 g·kg·d (mean ± 95% confidence interval) in Ox (r = 0.64) and 1.53 ± 0.32 g·kg·d in NB (r = 0.65), indicating a saturation in whole-body anabolism.
    
    Who: resistance-trained women aged about 23, studied in the luteal phase after a bout of whole-body resistance exercise, over roughly eight hours of recovery
    Effect: break point, that is the estimated average requirement, 1.49 g/kg/d (95% CI ±0.44) by oxidation and 1.53 g/kg/d (±0.32) by net protein balance; the safe intake at the upper confidence limit sits at the top of the 1.2 to 2.0 g/kg/d range recommended for athletes
    Certainty: eight participants, one session, and it measures whole-body anabolism over an eight-hour recovery window rather than long-term health or muscle gain; athlete-specific recommendations had until then rested almost entirely on studies in men
    Malowany et al., Medicine & Science in Sports & Exercise, 2019 · checked 2026-09-17 · we read the abstract