For most people who train and eat enough protein, the source makes little difference to muscle gained. Across 18 randomised trials, plant and animal protein gave similar gains in absolute lean mass and strength overall, though percent lean mass favoured animal protein2, and in a 10-week training trial vegan and meat-eating young adults grew the same amount of thigh muscle4.
Animal protein does keep a small edge in short lab measurements, especially in older adults6. Whether that edge matters depends on how much protein is eaten in total.
Why animal protein was expected to win
Protein quality depends on its amino acids, the building blocks protein is made of, and how easily they are digested. Animal protein provides all the essential amino acids in sufficient amounts and tends to be well digested; plant protein is generally less digestible and lower in some essential amino acids2. Short lab studies found that the fastest-digesting milk protein raised muscle protein synthesis (how fast muscle builds new protein) more than soy, likely because it carries more leucine, an amino acid that acts as a building signal1.
The catch is that those lab studies last a few hours. Muscle is built over weeks. So the useful question is what happens in longer training trials.
What was studied
| Type of study | What it measures | Time frame |
|---|---|---|
| Lab studies of muscle protein synthesis | Building rate after a protein dose | Hours to days |
| Meta-analyses of training trials | Lean mass and strength | Weeks to months |
| Whole-diet trials | Vegan vs mixed diet, protein matched | 9 days to 12 weeks |
A meta-analysis pools many trials into one estimate. Lean mass is everything in the body except fat, mostly muscle and water, measured by scan.
What the long-term trials found
Soy vs animal protein, 2018. Nine trials with 266 people compared soy with milk-based, beef or dairy protein alongside resistance training. Strength and lean mass rose in both, with no difference between groups1.
Plant vs animal protein, 2021. Eighteen randomised trials lasting 14 days to 2 years compared plant sources (soy, pea, rice and others) with animal sources (milk, meat and others)2. The pooled result:
- Absolute lean mass: no significant difference (0.22 kg favouring animal protein, 95% CI −0.02 to 0.46).
- Percent lean mass: favoured animal protein.
- Strength: no difference in squat, grip or leg strength.
- Under 50: animal protein gave a small, significant edge of 0.41 kg lean mass (95% CI 0.08 to 0.74). 50 and over: no difference.
The confidence interval (CI) is the range the true value most likely sits in. When it crosses zero, the data are consistent with no difference.
Animal minus plant protein: change in lean mass · kg
The authors warn that both lean-mass results were not stable: removing single trials changed whether the result was significant2. Their own summary still leans one way: animal protein "tends to be more beneficial for lean mass", especially in younger adults.
In plain terms: pooled over many trials, the edge for animal protein was small and fragile.
Whole diets, protein matched
Two trials changed the entire diet, not just a single protein drink.
Habitual vegans vs omnivores, 2021. Nineteen young vegan men and nineteen omnivores trained twice a week for 12 weeks, with protein brought up to about 1.6 g per kg a day (soy for the vegans, a milk protein for the omnivores)3. Leg lean mass rose by 1.2 kg on average in both groups. Muscle cross-sectional area, fibre size and leg press strength also rose, with no difference between groups on any measure.
Vegan vs omnivorous diet, 2023. Twenty-two young adults, men and women, did high-volume training five days a week for 10 weeks on about 2 g of protein per kg a day4. Thigh muscle volume, measured by MRI, rose 8.3% in both groups. Muscle fibre size rose 33% and 32%. Strength rose comparably.
Muscle gains over 10 weeks: omnivorous vs vegan diet · %
Omnivorous Vegan
The vegan diet in that trial got much of its protein from mycoprotein, a fungus-based protein. The study was funded by a company that makes it, which is worth weighing4.
In plain terms: when total protein was high and matched, a vegan diet supported the same gains over 10 to 12 weeks.
The latest lab evidence
A 2025 trial fed 40 active young adults an omnivorous or vegan diet at 1.1 to 1.2 g of protein per kg a day, with the protein either balanced across five meals or loaded toward the last meal, during 9 days of training5. Daily muscle building rates did not differ between any of the four groups.
Daily muscle building rate by diet and meal pattern · %/day
A 2026 meta-analysis of 12 lab studies found the overall result "slightly favored" animal protein, but the difference was small, within normal fasting rates, and carried "substantial uncertainty"6. Adults aged 65 and over showed a modest advantage for animal protein; younger adults responded similarly to both. Most of the animal protein data came from milk.
What this does and does not mean
It does not mean every plant protein equals every animal protein. Plant sources in these trials varied, and some are lower in certain essential amino acids. The whole-diet trials combined sources and kept totals high.
It does not rule out a small edge. The 2021 meta-analysis found one in adults under 50, and the 2026 lab review in adults over 65. Both edges were small and uncertain, and they point in different age groups, which is a reason for caution.
Total protein carried the result. The trials that found no difference fed about 1.6 to 2 g of protein per kg a day34. How to reach similar totals on a plant-based diet is covered in vegan macros, and where the daily targets come from in how much protein per kg. The per-meal side is in how much protein your body can use in one meal.
What the studies found
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Messina et al., *IJSNEM*1 | Meta-analysis of 9 trials, 266 people, with training | Soy and animal protein: same gains in strength and lean mass | 2018 |
| Lim et al., *Nutrients*2 | Meta-analysis of 18 randomised trials, adults | No difference in absolute lean mass or strength; percent lean mass favoured animal protein; small lean-mass edge for animal protein under 50 | 2021 |
| Hevia-Larraín et al., *Sports Med*3 | 19 vegan and 19 omnivorous young men, 12 weeks | Same gains in leg lean mass, muscle size and strength | 2021 |
| Monteyne et al., *J Nutr*4 | 22 young adults, 10 weeks, high protein | Thigh muscle volume +8.3% in both groups | 2023 |
| Askow et al., *MSSE*5 | 40 active young adults, 9 days | Vegan vs omnivorous: same daily muscle building | 2025 |
| Mendes et al., *J Acad Nutr Diet*6 | Meta-analysis of 12 lab studies, adults 18 to 85 | Slight, uncertain edge for animal protein, clearest over 65 | 2026 |
Limits worth knowing
- Small trials. 22 to 40 people in the whole-diet trials.
- Mostly young adults. The whole-diet trials were in adults in their twenties; older adults are where the lab data lean most toward animal protein.
- Mixed populations in the pooled data. Four of the 18 trials in the 2021 meta-analysis were in people with medical conditions2.
- Funding. The 2023 trial was funded by a maker of the fungus-based protein it used4.
- Abstract only. We read the 2018, 2021 (vegan trial), 2025 and 2026 papers as abstracts and use only their stated numbers.
Latest research
The newest paper we opened is the 2026 meta-analysis of 12 lab studies6. Its point estimates favoured animal protein, most in adults 65 and over, but the authors say the small number of studies and imprecise estimates "limit the strength of conclusions" and call for more high-quality trials. Nothing in it contradicts the training trials: it measured building rates over hours, not muscle gained over weeks.
The short version
- With enough total protein and training, plant and animal protein gave similar muscle and strength gains.
- Animal protein keeps a small, uncertain edge in lab measurements, most in older adults.
- The trials with no difference fed about 1.6 to 2 g of protein per kg a day.
- Total protein, not its source, is the part the trials agree on.
Educational overview only — not medical advice.
