You have probably been told you need more protein because you are plant-based. More to compensate for what plant protein lacks. More to make up for lower quality. More because it is just not the same.
A 2025 review of forty-three randomized trials comparing plant with animal protein never compared amounts: in every trial, both groups got a similar amount of protein. What it tested was the source. Soy held up against milk. The other plant proteins it could pool did not.
The number on this page — about 1.6 grams of protein per kilogram of body weight a day — comes from the design of a twelve-week training study. Its researchers brought nineteen vegans and nineteen meat eaters to that level, which they called optimal, citing an earlier review. The vegans topped up with soy protein, the meat eaters with whey.
Both groups gained leg lean mass, muscle size, muscle-fibre size and leg-press strength. On every one of those measures, the vegans kept pace.
That number is one variable in the complete plant-based fitness evidence — covering the dose, the soy question, the blending fix, and how the equation shifts after 40.
What the study cannot tell you is whether 1.6 is the right number. Everyone in it got 1.6, so it says nothing about what more or less would have done. It shows 1.6 was enough for vegans to keep up — not that anything above it is wasted. If you have been aiming for one gram per pound, about 2.2 grams per kilo, nothing in these trials says that is too much — or that you need it.
The thirty-eight men were young and new to lifting, and they were not randomly assigned: they were grouped by the diet they already ate.
The widely repeated rule that vegans need ten to twenty percent more protein than omnivores has no primary source in the evidence we examined. None of these trials tested it. None of the reviews derived it. We could not trace it to a study.
Soy Against Milk
The protein source debate has been framed as a quality question: is plant protein good enough? Seventeen head-to-head randomized trials compared soy protein directly against milk protein for muscle mass.
Pooled, they found no difference.
The gap came to −0.02 on a scale where the review counts 0.2 as a small effect. The review then split the trials by age, under and over sixty, and by sex. Soy and milk protein still did not differ.
Every trial in the review had to give both groups a similar amount of protein: within five grams for supplements, the same share of daily energy for whole diets. So this is a result about the source, at matched amounts — soy protein built as much muscle as milk protein.
Eating enough is where a plant-based plate turns against the lifter — three satiety mechanisms built into the diet suppress the caloric surplus needed to grow, and none of them involve protein quality.
Seventeen Trials, Five Trials
The asterisk is real and worth naming plainly. The result above is for soy. Soy has seventeen randomized trials behind it. Other plant proteins — rice, oat, potato and chia — have five. In those five, animal protein built more muscle. Seven trials of plant-based diets, matched to the animal-protein diets for protein, came out behind too.
The review’s authors call the reason unclear. Rice and potato protein isolates carry more essential amino acids, as a share of their protein, than soy — so their amino acid content alone does not explain it. And the one chia trial among the five favoured the plant protein.
One trial tested a blend of wheat, corn, and pea protein designed so that each source covers what the others lack.
Pea brought lysine. Corn brought leucine and methionine. Together, they raised essential amino acids in the blood about half as much as milk protein — yet the muscle-building rate over the next five hours did not differ.
This is one study: twenty-four young men, at rest, one thirty-gram drink, five hours of measurement. None of the trials we examined has tested this blend over months of training.
Five Hours Out of Twenty-Four
The argument against plant protein has leaned on what happens in the first few hours after a meal. Eat plant protein, measure the muscle-building spike, and it tends to come out a little lower than after whey or milk.
But that spike captures a five-hour window. Your body builds muscle over twenty-four.
When researchers pooled the studies measuring this signal — twelve that met their criteria — the difference between plant and animal protein was negligible in size, and they rated their certainty in it as low. In younger adults it was close to zero. In older adults it leaned more clearly towards animal protein.
Then compare that lab signal with what happened to muscle over weeks and months. The forty-three-trial review’s authors point to the same mismatch: short-term studies suggest milk protein does better, while the long-term soy trials found soy and milk alike. They cite earlier work showing the short-term signal is a poor predictor of long-term muscle growth.
For soy, the lab-versus-training contradiction is a mismatch between what the test captures and what the body builds over months. For the other plant proteins, the long-term trials did show a gap.
Where the Gap Showed Up
The review also split its results by age and by sex, across the thirty trials it pooled for muscle mass.
Women showed no difference between plant and animal protein. In men, a trend towards animal protein fell short of statistical significance. Adults over sixty showed no difference in muscle mass — though for lower-body strength, animal protein came out ahead in that age group.
The gap was clearest in younger adults, and in trials that paired protein with resistance training — the lifters this page is written for. Those figures pool soy, the other plant proteins and plant-based diets together. For soy against milk alone, neither age nor sex made a difference.
What about soy and testosterone? A 2025 dose-response meta-analysis pooled eight trials with three hundred and twenty-nine men: soy did not significantly change total testosterone. Estradiol did not change overall, though it rose in shorter trials and in trials without exercise. The hormone question has its own deep dive elsewhere on this site.
Can you hit the number without supplements? In the twelve-week study, the vegans took about 58 grams of soy protein a day on top of their food to reach 1.6 grams per kilo; the meat eaters took 39 grams of whey. The vegans needed more because they started from a lower intake. For a lighter person, whole foods alone can get there. For a heavier person, a plant protein supplement closes the gap.
Based on what we examined — a forty-three-trial review, a review of twelve short-term studies, a twelve-week training study and a single-meal trial — the evidence points to this: soy protein builds as much muscle as milk protein when the amounts match; the other plant proteins pooled so far did less well.
No trial here sets a separate protein target for plant-based lifters. The twelve-week study used about 1.6 grams per kilo a day for both groups, and the vegans in it kept pace.
One question the daily total does not settle: does it matter how you split those grams across meals? One trial matched a plant blend to milk protein on leucine — 2.4 grams per serving — and found no difference in the muscle-building response over five hours. That per-serving architecture sits in a different analysis.
For a 75 kg (165 lb) person, 1.6 g/kg means roughly 120 grams of protein per day. That is about what you would get from a tofu scramble at breakfast, a lentil bowl at lunch, a soy protein shake after training, and a tempeh stir-fry at dinner.
For context: a 75 kg omnivore at the same level eats 120 grams too — same number, different packaging. The vegans in the 12-week study took about 58 grams of soy protein a day on top of their regular diet to reach this level, the omnivores 39 grams of whey. The vegans needed about 19 grams more because they started lower.