Match the dose and the outcomes match#
Protein source matters far less than the amount you eat, and the strongest evidence is the most direct: match a plant-based diet and a mixed diet at the same daily protein, train both, and they produce the same muscle. The scoreboard difference between plant and animal protein is real, but it is small, it shows up in specific places — single meals and older muscle — and it is closed by eating more protein rather than by eating an animal.
Which makes this a story about when the gap appears rather than whether it exists. The quality ranking explains why plant proteins score lower on amino acid tests, and that ranking is sound. What is surprising is how poorly those scores predict what happens in a human being over twelve weeks. Assume you have read how much protein per day for the target itself; this is about which foods fill it.
Twelve weeks, matched protein, identical results#
The cleanest design compares people who already live the diets. Nineteen habitual vegans and 19 omnivores — matched in age and body mass, all young men — did 12 weeks of twice-weekly supervised resistance training. Both groups were brought to roughly 1.6 g/kg/day of protein, the vegans using soy isolate and the omnivores whey1.
Both groups grew, and they grew the same amount:
| Outcome (12 weeks) | Vegan | Omnivore |
|---|---|---|
| Leg lean mass | +1.2 ± 1.0 kg | +1.2 ± 0.8 kg |
| Rectus femoris CSA | +1.0 ± 0.6 cm² | +0.9 ± 0.5 cm² |
| Vastus lateralis CSA | +2.2 ± 1.1 cm² | +2.8 ± 1.0 cm² |
| Leg-press 1RM | +97 ± 38 kg | +117 ± 35 kg |
No between-group difference reached significance1. The authors' conclusion is worth stating precisely, because the caveat is inside it: an exclusively plant-based diet at ~1.6 g/kg/day "is not different than a protein-matched mixed diet." Protein-matched is doing the work. The vegans hit 1.6 g/kg with the help of soy isolate — the authors themselves noted that reaching that number on whole plant foods alone is difficult. The trial shows the source doesn't matter once the dose is equal. It does not show the dose is equally easy to reach.
Where the gap is real: one meal, older muscle#
Now the other side, and it is not a rhetorical concession — it is a genuinely different result.
Sixteen older adults (65–85, eight men and eight women) ate, on separate occasions, a whole-food omnivorous meal built around 100 g of lean ground beef, or an isocaloric and isonitrogenous whole-food vegan meal. Both delivered 0.45 g of protein per kg of body mass. Muscle protein synthesis over the following hours ran 0.052 ± 0.023 %/h after the meat meal versus 0.035 ± 0.021 %/h after the vegan meal — roughly 47% higher, P = 0.037. Plasma essential amino acids rose further and faster after the meat (incremental AUC 87 ± 37 vs 38 ± 54 mmol·6 h/L, P-interaction < 0.01)3.
That is a big, real, single-meal difference in exactly the population that can least afford it.
The same lab found the opposite — and the reason is the finding#
Here is where it gets instructive. The same research group ran a similar comparison in young men using isolated proteins: 30 g of milk protein against a 30 g plant blend of 15 g wheat, 7.5 g corn, and 7.5 g pea protein.
The amino acid delivery was not close. Milk produced far greater essential amino acid availability (incremental AUC 151 ± 31 vs 79 ± 12 mmol·300 min/L, P < 0.001), with peak leucine 25% higher and peak lysine 85% higher. By every marker protein-quality scoring cares about, milk crushed the blend.
And myofibrillar protein synthesis did not differ: 0.053 ± 0.013 %/h for milk versus 0.064 ± 0.016 %/h for the plant blend, P = 0.08 — numerically higher for the plants2.
Milk delivered 25% more leucine and 85% more lysine into the blood. The muscle built protein at the same rate either way. The amino acid curve is not the outcome.
So what separates the two results? Two things, and both are nameable rather than mysterious. The 2024 study used older adults, whose muscle is measurably harder to stimulate, and whole foods, where the food matrix slows and blunts amino acid release. The 2022 study used young adults and isolates, where a plant blend can be engineered to deliver a competent amino acid profile. Same lab, same methods, opposite conclusions — because the moderators are the answer. Age and food form decide whether the source gap shows up at all.
The declared interests here run in every direction, which is the point. The plant-blend study was funded by TiFN, with sponsors Tereos Syral, Cargill, and Kellogg partly financing the project, and two authors disclosing research grants, consulting fees, or honoraria from Friesland Campina (dairy), Tereos Syral, and Pepsico2. This is a field where plant-protein processors, dairy companies, and meat producers all fund work — and the plant-favorable result and the meat-favorable result above came from the same group. Read that as a reason to weigh the pattern across studies rather than any single one, in either direction.
Zoom out to a whole day and the gap closes#
If a vegan meal produces less muscle protein synthesis, you would expect a vegan day to as well. It doesn't.
Thirty-four physically active older adults (72 ± 4 years) ate a controlled vegan diet for 10 days and a controlled omnivorous diet (60% animal protein) for 10 days, isocaloric and isonitrogenous, in randomized order. Daily muscle protein synthesis, measured with deuterated water across the whole period, came out at 1.23 ± 0.04 %/d on the vegan diet and 1.29 ± 0.04 %/d on the omnivorous diet — P = 0.2542. The vegan diet also lowered LDL and total cholesterol (both P < 0.0001)4.
A meal-sized deficit did not become a day-sized deficit. Variety across the day did what quality could not do in a single sitting.
The authors' framing matters: a well-balanced vegan diet "providing a variety of plant-based protein sources" is what does not compromise daily synthesis. That is the practical instruction hiding in this whole literature — variety across the day substitutes for quality within the meal.
What the pooled trials say#
The meta-analytic view is consistent with all of the above, and appropriately unexciting. Across 18 randomized controlled trials comparing animal protein (whey, casein, milk, beef) against plant protein (soy, pea, rice), animal protein produced a small advantage in percent lean mass (WMD 0.50%, 95% CI 0.05 to 0.95) while absolute lean mass did not separate (WMD 0.22 kg, 95% CI −0.02 to 0.46). Strength showed nothing at all — not 1-RM squat, grip, knee extension, or knee flexion. Splitting by age, the advantage sat entirely in adults under 50 (absolute lean mass WMD 0.41 kg, 95% CI 0.08 to 0.74); in adults 50 and over there were no significant differences5. Those authors declared no conflict of interest and were funded by the National University of Singapore.
Note the shape of that result: the effect that survives is a percentage of lean mass, in the young, on the outcome most sensitive to small shifts — and it disappears in absolute kilograms and in every strength measure. That is what a real but marginal effect looks like.
So what should you actually do?#
If you eat animal protein, nothing here asks you to change. If you don't, three things follow from the evidence rather than from ideology:
Eat more protein, not different protein. The 12-week parity was bought at 1.6 g/kg — see how much protein to build muscle for why that number and not another.
Use variety, not a single hero food. The 10-day parity came from a diet drawing on a range of plant sources, which is the mechanism that replaces per-meal quality — the logic behind complete vs incomplete proteins.
Pay more attention if you are older. Both places the gap appeared involved older muscle or a single whole-food meal. That argues for larger, more concentrated protein servings rather than for abandoning plants. Protein for vegetarians and vegans covers the practical build.
FAQ#
Can you build the same muscle on a vegan diet?#
Yes, at a matched protein intake. Nineteen habitual vegans and 19 omnivores brought to ~1.6 g/kg/day and trained for 12 weeks gained statistically indistinguishable leg lean mass, muscle cross-sectional area, and strength1. The caveat is the matching itself: the vegans used soy isolate to reach 1.6 g/kg, which the authors noted is hard to hit on whole plant foods alone.
Why do plant and animal protein give the same result if the amino acids differ?#
Because amino acid delivery is not the outcome — it is a proxy for it. When 30 g of milk protein was tested against a 30 g wheat-corn-pea blend, milk delivered nearly double the essential amino acids, 25% more peak leucine and 85% more peak lysine, yet myofibrillar protein synthesis was no different (0.053 vs 0.064 %/h, P = 0.08)2. Above a sufficient dose, more amino acids in the blood stop translating into more muscle protein.
Does age change whether protein source matters?#
Yes — it is the clearest moderator in the literature. Pooled across 18 RCTs, animal protein's small lean-mass advantage appeared only in adults under 50 (WMD 0.41 kg, 95% CI 0.08 to 0.74) and vanished in those 50 and over5. But at the single-meal level the reverse pressure applies: in adults aged 65–85, a beef meal drove ~47% higher muscle protein synthesis than an isonitrogenous vegan meal3 — while a full vegan day matched an omnivorous one4.
Sources#
- Hevia-Larraín V, et al. High-Protein Plant-Based Diet Versus a Protein-Matched Omnivorous Diet to Support Resistance Training Adaptations: A Comparison Between Habitual Vegans and Omnivores. Sports Med. 2021.
- Pinckaers PJM, et al. The Muscle Protein Synthetic Response to the Ingestion of a Plant-Derived Protein Blend Does Not Differ from an Equivalent Amount of Milk Protein in Healthy Young Males. J Nutr. 2022.
- Pinckaers PJ, et al. Higher Muscle Protein Synthesis Rates Following Ingestion of an Omnivorous Meal Compared with an Isocaloric and Isonitrogenous Vegan Meal in Healthy, Older Adults. J Nutr. 2024.
- Domić J, Pinckaers PJM, Grootswagers P, et al. A Well-Balanced Vegan Diet Does not Compromise Daily Mixed Muscle Protein Synthesis Rates when Compared with an Omnivorous Diet in Active Older Adults: A Randomized Controlled Cross-Over Trial. J Nutr. 2025.
- Lim MT, Pan BJ, Toh DWK, Sutanto CN, Kim JE. Animal Protein versus Plant Protein in Supporting Lean Mass and Muscle Strength: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients. 2021.
