Whey stops paying off past 30–35 g a day
In short
Across 36 randomised controlled trials (1,552 participants) pairing protein supplements with supervised resistance training, whey ranked first for lean body mass (SUCRA 0.91; +1.24 kg vs placebo, 95% CrI 0.61–1.87). The dose-response curve flattened at 30–35 grams a day, with no additional gain observed above that. Milk protein (+1.18 kg) and casein (+0.92 kg) followed closely, and plant proteins showed smaller effect estimates — though the evidence certainty there was low to very low.
The whey dose-response curve flattens at 30–35 grams a day. That comes from 36 randomised controlled trials — 1,552 participants across 89 trial arms, all pairing supplementation with at least six weeks of supervised resistance training, connected into an eight-node Bayesian network. The extra cost of going from 30 g to 45 g did not come back as measured lean mass.
The ranking ran whey (SUCRA 0.91, +1.24 kg vs placebo), milk protein (0.78, +1.18 kg), casein (0.72, +0.92 kg). The 0.06 kg gap between first and second is worth reading literally: pick any dairy-derived protein and the outcome is roughly the same.
So is 30 grams enough protein for the day?
No. That figure is supplemental protein, not daily total intake. Protein from food was not what these trials compared. Going from two scoops to three is a separate question from hitting your daily number.
How big is 1.24 kg, really?
It is the share the supplement added over six or more weeks of training — the gap against placebo, not the total gain from lifting. Training itself moves the far larger number, and supplementation stacks on top of it. Reverse that order and you end up adding scoops while the sets stay the same.
Does this change after 65?
Whey's advantage narrowed in older adults. Its SUCRA slipped from 0.92 in younger participants to 0.89, while casein climbed from 0.68 to 0.76. That fits the usual reading of slow-digesting casein covering longer fasted windows such as overnight. The authors flag that this subgroup rests on only nine trials and the ranking shift may be unstable. See also training hard after 50.
Are plant proteins out?
Soy, pea and rice showed smaller effect estimates than dairy-derived protein. But evidence certainty was low to very low and the credible intervals were wide. Nothing here justifies forcing down whey if lactose or digestion makes dairy a problem.
For a relative strength score, this is a denominator story as much as a numerator one. A score that normalises your Big 3 total against bodyweight rewards adding lean mass while holding weight steady — and 1.24 kg is the unit that creates that room. Priorities between total intake and timing are covered in protein timing versus total intake.
The authors labelled the 30–35 g figure exploratory themselves. It comes from fitting restricted cubic splines to the pooled data, and the optimum can shift with bodyweight and training volume. Do not read it as a hard ceiling.
Frequently asked questions
How much whey protein should I take per day?
In an analysis of 36 randomised trials pairing supplementation with resistance training, the whey dose-response curve flattened at 30–35 grams a day, with no additional lean mass gain observed above that. Note this is supplemental protein, not total daily protein intake.
Is whey or casein better for building muscle?
Across all participants whey ranked first (SUCRA 0.91, +1.24 kg lean body mass versus placebo), with casein third at 0.72 and +0.92 kg. In adults over 65 the gap narrowed, with casein rising from 0.68 to 0.76.
Do plant protein supplements build muscle?
Soy, pea and rice protein showed smaller effect estimates than dairy-derived protein, but the evidence certainty was low to very low with wide credible intervals, so the difference is not settled. If lactose or digestion rules out dairy, plant protein remains a reasonable choice.
How much extra muscle does a protein supplement actually add?
With six or more weeks of resistance training, whey groups gained an average of 1.24 kg more lean body mass than placebo groups (95% CrI 0.61–1.87). That is the supplement's added share, not the total gain produced by training.
Source: PubMed