Protein for lifters: three numbers and where they came from

One point six grams per kilogram. Twenty to thirty grams a meal. Protein every three hours. Three numbers, repeated everywhere, usually without a source.

Each traces to a real, identifiable study. In every case the study is narrower than the rule built on top of it, and in every case the effect is smaller than the confidence of the advice suggests.

Where 1.6 g/kg comes from, and what it actually is

The source is a 2018 meta-analysis of 49 randomized trials covering 1,863 people doing resistance training for at least six weeks. Protein supplementation increased one-rep-max strength by about 2.5 kg and fat-free mass by about 0.3 kg. A breakpoint analysis found gains in fat-free mass plateaued at 1.62 g/kg/day.

Three things get dropped when that number is quoted:

• The confidence interval was 1.03 to 2.20 g/kg. “1.6” is the middle of a wide range, not a threshold anyone measured precisely.
• It is the point beyond which extra supplementation stopped adding anything. It is a ceiling on the benefit of more, not a floor you must reach.
• The effect being plateaued is small. Roughly 0.3 kg of fat-free mass over six weeks or more.

The analysis also found supplementation worked better in people who already lift and worse with increasing age. An independent dose-response meta-analysis from a different research group reached broadly compatible conclusions, which is worth more than either paper alone.

A larger 2022 review of 74 trials put it plainly: increasing daily protein produces small additional gains in lean mass and lower-body strength for people doing resistance exercise. Small is the operative word, and it is not how protein is usually sold.

“Every three hours” is a twelve-hour study

The meal-timing rule comes from a 2013 study in trained young men that compared three feeding patterns after a resistance session: eight servings of 10 g, four of 20 g, or two of 40 g, spread across twelve hours of recovery. The four-by-20 g pattern produced the best myofibrillar protein synthesis over that window.

What the study did not do is follow anyone for longer than twelve hours, measure muscle mass, or run a training intervention. It is an acute measurement of a short-term signal.

The per-meal ceiling is on shakier ground than the ceiling talk suggests

The claim that your body can only use 20 to 30 g of protein in a sitting is often attributed to a 2018 paper. That paper is a narrative review, a considered discussion of the literature rather than an experiment, and it is regularly cited as if it were primary evidence.

More usefully, a 2023 study using intrinsically labeled protein and a twelve-hour measurement window found the anabolic response to a large protein dose had no clear upper limit in magnitude or duration. Its own limits are real: an acute stable-isotope study, small sample, single comparison, no long-term body-composition outcome.

So the honest position is that the per-meal ceiling is weakly evidenced, and its recent contradiction is also from a short acute study. What is not supported is either extreme: neither “only 25 g counts” nor “eat 100 g at once for more muscle” is something the evidence establishes.

What this means if you lift

Get somewhere in the region of 1.6 g per kg of bodyweight per day if it is easy to do, knowing the useful range around that is wide and the returns near the top of it are small. Spread it across the day in a pattern you will actually repeat, since the timing evidence is a twelve-hour proxy rather than a rule. Do not worry about a per-meal cap that rests on a narrative review.

And keep the size of the prize in view. The meta-analytic effect of raising protein in people who already train is consistently described as small. Protein is worth getting roughly right and not worth optimizing to the gram, which is the opposite of how it is usually discussed.

FitTrack’s Food Check exists for the roughly-right version of this: type the protein, carbohydrate and fat off a label and see how it lands, without a food database or an account. The daily targets and the diary are the parts Pro charges for.