Whey vs Plant Protein: Strength Came Out the Same. The Lean-Mass Edge Was Under a Pound, in People Under 50.

Somebody put animal protein and plant protein against each other, in randomised trials, and measured what happened to muscle. Sixteen trials went into the pool, out of 3,081 papers screened. [1]

Strength: no difference. Absolute lean mass: no difference. [1] Those are the two outcomes anybody buying a tub actually cares about.

Then it gets more interesting, and this is where both sides of the marketing start quoting selectively.

What the head-to-head actually found

Percent lean mass did favour animal protein, and in adults under 50 there was a real edge in absolute terms: 0.90 lb (0.41 kg). [1]

Under a pound. Over the course of a trial. That is the biggest honest number on this page and it is worth seeing at full size before anybody sells you a conclusion with it.

And one of those numbers is closer to nothing than it looks

The percent-lean-mass edge in under-50s was 0.50%, with a range of 0.00 to 1.01. [1]

That range is a confidence interval — the span the true answer probably sits inside. When it includes zero, “no effect at all” is still on the table. This one does not merely come close to zero. Its lower edge is zero.

So the honest way to say it is: animal protein probably has a small edge on that measure in younger adults, and no edge whatsoever is still inside the range the data allows. This is what our ratings mean.

The newest analysis ranks whey top — and grades itself weakly

A 2026 network analysis pooled 36 randomised trials and 1,552 people, comparing whey, casein, milk, soy, pea, rice and blends against placebo alongside resistance training. [2]

Whey came first for lean body mass, at 2.7 lb (1.24 kg) more than placebo, with milk and casein just behind. Its dose-response curve flattened out at 30–35 g a day, which is a more useful number than the ranking. [2]

Now the sentence the ranking gets quoted without. The reviewers write that plant proteins showed smaller effect estimates than dairy ones, “but the evidence certainty was low to very low and the credible intervals were wide, limiting firm conclusions”. [2]

That is the authors grading their own plant-protein comparison as weak. A first-place ranking built on low-to-very-low certainty is a league table with most of its matches unplayed.

The condition that makes all of this readable

Here is the detail that changes how you should read every number above. In those head-to-head trials, total protein intake was already above the recommended amount — at the start and at the end. [1]

So what was compared was two adequate protein intakes from different sources. That is precisely the situation where the source should matter least, because the thing that drives muscle is getting enough protein in total — and that part is settled, at about two-thirds of a pound of extra lean mass across 49 trials, and nothing at all without the training.

What these trials do not tell you is whether source matters when total protein is low. Nobody ran that comparison here. Not disproved — untested.

So which tub

On the evidence: if you are hitting your protein target, the source is a much smaller lever than the marketing on either tub implies. Strength came out the same. Absolute lean mass came out the same. The measurable edge for dairy was under a pound, in the younger half of the sample, on one measure whose interval touches zero.

Two things do follow from the evidence, and they are both practical:

— Whey plateaus around 30–35 g a day. [2] Past that you are buying scoops that the dose-response curve says are doing nothing extra.
— Plant protein is not disqualified — it is under-studied. “Low to very low certainty” is a statement about the evidence, not about the food.

Neither industry comes out of this well. Dairy marketing sells a gold standard the head-to-head trials did not find on strength. Plant marketing sells “just as good” on an evidence base its own reviewers call weak. If you bought either on the strength of a claim like that, the claim was ahead of the research — that is a fault of the label, not of you.

Elsewhere: protein while dieting, whether it actually keeps you full, the one supplement that survived a screen of 250, and what training does after 60. The whole shelf is ranked here.