Researchers checked five different ways. The results should have settled everything — until one test almost cracked the tie.
“Five measurements — from a full-leg body scan down to individual muscle fibers under a microscope. Zero differences between vegans and meat-eaters. Not one.”
Someone in your group chat just dropped a reel. A fitness influencer showing vegan muscle gains, caption claiming plant protein builds just as much muscle as whey. Half the chat agrees. The other half already typed their rebuttal.
Both sides are missing something.
A research team at the University of São Paulo spent 12 weeks testing what actually happens when habitual vegans and lifelong meat-eaters train side by side under the exact same supervised program. Not a weekend experiment with people trying tofu for the first time.
These were 19 men who had been eating exclusively vegan for at least a year — some for over a decade — matched against 19 omnivores of the same age, weight, and fitness level. All 38 were untrained young men between 18 and 35 who hadn't lifted weights regularly in over a year.
Both groups ate the same total protein — 1.6 grams per kilogram of body weight per day. The vegans supplemented with soy protein. The omnivores supplemented with whey. Same gym. Same exercises. Same coach watching every rep.
Then came the part that separates this study from every comparison you've seen shared in a group chat. Instead of checking the results one way and calling it settled, the researchers checked five completely different ways.
Plant protein built the same muscle as animal protein across every measurement — but the full story has three parts, not one.
- Five independent measurements — from full-leg body scans to individual muscle fibers — showed no difference in muscle growth between vegans and meat-eaters over 12 weeks.
- The vegan group needed larger daily protein servings to reach the same total protein target, because plant protein delivers less of the key muscle-building amino acid per gram.
- Leg strength was the one result that came closest to showing a gap — the meat-eaters gained more, but not enough to be statistically conclusive.
- A separate meta-analysis pooling nine trials and 266 participants from different labs confirmed the same equivalence for muscle mass and strength.
- The researchers specifically cautioned that these results may not apply to older adults, where protein source appears to play a larger role.
Five Measurements, One Answer
The researchers started with a body scan — a machine called DXA that maps exactly how much lean tissue sits on each leg. After 12 weeks, both groups had gained exactly the same amount of leg muscle: 1.2 kilograms each. Then they zoomed in closer — ultrasound on a single thigh muscle, the kind that fires during a squat. Same growth. No gap.
Still not satisfied, they went microscopic. A tiny sliver of muscle tissue from each participant's thigh, individual fibers examined under a microscope. Two types of fiber sit inside every muscle — slow-twitch for endurance, fast-twitch for power. Both types had grown equally in vegans and meat-eaters.
Finally, they stepped all the way back out and scanned total lean mass across the entire body. Same answer. Body scanner, ultrasound, microscope — every tool told the same story.
That is not one test getting lucky. When you check the same question from every angle and land on the same answer, that answer stops being debatable.
The Part the Reel Left Out
If this were the whole story, the reel in your group chat would be right. Same protein, same results, end of debate. But the study measured something else — something nobody in the comments section is mentioning.
To hit that shared protein target, the vegan group needed roughly 50% more protein powder every day than the omnivore group. About 58 grams of soy protein compared to 39 grams of whey. Same muscle gains at the end. But a noticeably bigger scoop at the start of each day.
The vegans weren't doing anything wrong. Their habitual diets simply started with less total protein, which meant more supplemental powder was needed to reach the shared 1.6-gram target. Equal destination. Different ticket price.
The study's vegans hit their protein target using concentrated soy protein powder — not whole foods.
Getting that same amount from lentils, tofu, and beans alone would mean eating a lot more food, taking in more calories, and dealing with plant compounds that can actually slow down how much protein your body absorbs.
Why the Bigger Scoop
The reason comes down to one amino acid: leucine. It is the specific building block that acts as a trigger for muscle growth. Plant protein contains less of it per gram than whey — so more total powder is needed to deliver the same amount of leucine.
A 2024 study from a team including one of this study's own senior researchers found that adding a small amount of extra leucine to a plant protein blend brought its muscle-building signal up to match whey's. [1] The bigger scoop is not wasted volume. It is making sure enough leucine reaches the muscle to flip the same switch.
The One Result That Almost Cracked
Five measurements said equal. But the researchers also tested leg strength — how much total weight each group could press — and that result told a more complicated story.
The omnivores gained an average of 117 kilograms on the leg press. The vegans gained 97 kilograms. A 20-kilogram gap.
The statistical test came back at p=0.10 — meaning roughly a one-in-ten chance the gap is random noise rather than a real difference. Standard scientific practice draws the line at one in twenty. So officially, no significant difference. But it was the closest any outcome in the entire study came to breaking the tie.
Every other measurement ranged from comfortably to overwhelmingly non-significant. This one stopped just short. Not proof that whey builds more strength. But not nothing, either. An honest reading does not dismiss it and does not overstate it. The muscle evidence is clear. The strength question stays open.
“Five measurements said the muscle was equal. One test — leg strength — came back at one-in-ten odds. Not enough to break the tie by the textbook. But enough to leave one question open.”
Where the Picture Changes
Everything above applies to young, healthy men eating enough total protein. That qualifier matters more than most comparisons bother to mention.
A 2024 study from the same extended research network tested what happens at the other end of the age spectrum — adults between 65 and 85. [2] After a single meal, the animal-source version produced roughly 47% higher muscle-building activity than an equally matched vegan meal. That difference was statistically significant.
This does not undo the 12-week finding. It scopes it. For young adults eating enough total protein and training consistently, the source appears not to matter for muscle. For older adults, the landscape shifts. The same broader research community produced both findings — a page that only tells you one of them is picking a side.
A dose-response study in that older population quantified the shift: the per-meal protein needed to reach peak muscle building rose roughly 60%. At that higher demand, the leucine gap between plant and animal widens further — and whether the bigger scoop still closes it past 65 is a question neither team has answered.
And the 12-week finding does not rest on a single study. A meta-analysis pooling nine separate trials and 266 participants found no difference between soy protein and animal protein for muscle mass or strength gains during resistance training. [3] The convergence across research teams and years makes the equivalence harder to dismiss as a one-off result.
The Three-Part Answer
The debate in your group chat has an answer. It is just not the one-word answer either side is selling.
Part one: muscle growth was equal across five independent measurements. Body scan, ultrasound, microscope — the vegans and meat-eaters built the same amount of muscle over 12 weeks of matched training and matched protein intake.
Part two: the cost was different. The vegans needed roughly 50% more protein powder to reach that same protein target, because plant protein delivers less leucine per gram.
Part three: one question stays open. Strength gains showed a gap that fell just short of statistical significance. It might mean something. It might not. The science has not fully closed that file.
The reel your friend shared oversimplified the science. Your instinct to dismiss it also oversimplified the science. The actual answer is more interesting than either position — and when you set it beside daily targets, per-meal capacity, aging, and five other protein variables, the source debate stops being a debate and starts being a detail — and now you are the person in the chat who knows all three parts of it.
The protein-source debate has a practical answer that most gym conversations miss.
What the research shifts is not whether plant protein works — it does — but where to focus your attention. Total daily protein matters more than where it comes from. But reaching that total on a plant-based diet takes more deliberate planning: larger servings, mixed sources, and an eye on leucine content.
The biggest open question is not about muscle size. It is about strength. The muscle evidence is thorough and settled. The strength story is not finished yet — and anyone claiming otherwise is ahead of the science.
What other research found
What this means for you
The muscle results are in your corner — across every measurement tool the researchers used, vegan and omnivore gains were identical. The practical takeaway from the data is about leucine, the amino acid that kickstarts muscle building.
Plant protein has less leucine per gram than whey, which is why this study's vegan group needed bigger daily servings of soy protein powder. Mixing your plant sources — combining grains with legumes, or looking for protein blends that include added leucine — is the strategy the broader research from this same lab points toward.
The study confirmed the path works. The attention goes to making sure enough leucine arrives with each serving.
The transition question this study answers is clear: matched protein intake produced matched muscle. The source did not create a gap.
The practical adjustment is about quantity, not quality. A plant-based approach means planning for slightly larger protein servings to reach the same daily total — the study's vegan participants started with less protein from food and needed more from supplements to close that gap.
One honest caveat: every participant in this study was new to weight training. Experienced lifters working closer to their ceiling may want to watch their results more carefully during a protein transition.
This study tested young men in their mid-twenties. The authors themselves flagged that older adults may respond differently.
A separate study from the same extended research network found that a single omnivorous meal produced roughly 47% more muscle-building activity than an equally matched vegan meal in adults between 65 and 85. That gap was statistically significant — unlike any of the gaps in the younger group.
The equivalence shown in this study may not extend to older adults, where the body becomes less efficient at using protein and the source may carry more weight.
Before you change anything
Young, healthy, untrained men only. All 38 participants were men between 18 and 35, living in Brazil, who had not lifted weights regularly for at least a year. No women were tested. No trained athletes. No one over 35.
Habitual dietary patterns, not assigned diets. The vegans had been vegan for at least a year — they were not randomly assigned to eat plant-based. This means pre-existing lifestyle differences between the groups (beyond just diet) could play a role.
Relied heavily on protein powder. The vegan group averaged 58 grams of soy protein isolate per day — a concentrated supplement, not whole foods. The results apply to plant-based diets with substantial supplementation, not necessarily to someone eating only beans and lentils.
Lower-body training only. The program trained legs exclusively. The authors note no reason upper-body results would differ, but it was not tested.
Vegans started with lower vitamin D. Baseline vitamin D was significantly lower in the vegan group (18 vs 24 ng/mL). This did not appear to affect muscle outcomes, but it is a nutritional difference worth noting.
Not randomized. Participants chose their own diets years before the study began. The researchers opted for this design to avoid the confounding effects of an abrupt dietary switch — a reasonable choice, but it means the groups may differ in ways beyond just food.
Twelve weeks may not be enough. Both groups gained substantial muscle in this timeframe, but whether small differences would emerge over six months or a year remains unknown.
Beginner lifters only. Untrained participants show large initial gains regardless of the details — the so-called newbie response. In experienced lifters, where the training stimulus is no longer dominant, protein source differences might matter more.
Dietary tracking relied on self-reporting. Participants logged their food through 24-hour dietary recalls every four weeks. This method is standard but known to be imprecise — people routinely under-report or over-report what they eat.
Strong for muscle equivalence. Five independent measurement tools all returned the same answer in the same direction. That internal consistency is rare and makes it hard to attribute the result to measurement error. A separate meta-analysis of nine trials (266 participants across multiple labs) confirmed the same conclusion.
Less settled for strength. The strength result (p=0.10) came from a single study with 38 participants. It was not significant, but it was the closest any outcome came to showing a difference. A larger study or longer duration could tip this either way.
Honest about scope. This evidence applies to young men eating enough total protein with the help of concentrated supplements. For older adults, for lower protein intakes, or for whole-food-only diets, the picture may shift — and the researchers said so themselves.
Source did not matter for muscle growth — but both groups needed 1.6 grams per kilogram per day to get there. That target did not come from this study alone.
A meta-analysis covering 49 controlled trials — 49 studies, 1,863 participants — landed on a ceiling in the same range. The number applies regardless of whether your protein comes from plants or animals.
What This Study Found
All findings from this paper, in plain language.
- Vegans and meat-eaters gained identical amounts of leg muscle over 12 weeks of training when eating the same total protein.
- Both groups grew the muscles in their thighs by the same amount, whether measured across the whole thigh or in a single large thigh muscle.
- Under a microscope, individual muscle fibers — both the endurance type and the power type — grew equally in vegans and meat-eaters.
- Leg press strength gained more in the meat-eating group, but the gap fell just short of being statistically meaningful.
- Vegans needed roughly 50% more protein powder per day than meat-eaters to reach the same total protein target.
- Meat-eaters consumed more of the key muscle-building amino acids at every meal, despite eating the same total protein.
- The vegans' daily leucine intake was still high enough to reach the point where extra leucine stops helping muscle growth.
- Both groups showed up and trained equally hard — ruling out effort differences as an explanation for the results.
- Reaching this protein level from whole plant foods alone would require eating significantly more food and taking in more calories.
- Checking results across body scans, ultrasound, and muscle biopsies all told the same story: no difference between groups.
- Mixing different plant protein sources — like grains with beans — may help cover the amino acid gaps that any single plant food leaves.
- Vegans started with significantly lower vitamin D levels, but this did not change the muscle or strength results.