You have probably been told to eat 1 gram of protein per pound of body weight. Your coach said it. The calculator confirmed it. A TikTok creator with millions of followers repeated it.
The research on that number is closer than either side admits. The biggest analysis of its time estimated that extra protein stops adding lean mass at about 1.6 grams per kilo, but that estimate is uncertain enough that its own authors suggest 2.2, which is 1 gram per pound, for those seeking maximum gains.
“If building muscle were a 100-point exam, the actual lifting scores 91 points. Your protein supplement scores 9.”
The answer lands in one sentence: the main estimate puts the point where extra protein stops adding lean mass at about 1.6 grams per kilogram of body weight per day — but it is uncertain, and its range reaches 2.2.
For an 80-kilogram person, 1.6 grams per kilo is about 130 grams. The popular 1-gram-per-pound target for that same person is 176 grams. Whether those extra 46 grams a day add anything is exactly what the evidence cannot settle yet.
What was then the largest meta-analysis on this question pooled 49 randomised controlled trials covering 1,863 participants who lifted weights for at least six weeks.
A statistical cutoff analysis estimated that protein intake beyond about 1.62 grams per kilo stopped producing further gains in lean mass. In 2022, a team that shared two of its authors ran a larger analysis (74 trials, over 2,600 participants in its lean-mass analysis) and found a larger effect at 1.6 grams per kilo or more than at 1.2 to 1.59. Its highest category was 1.6 or more, so it could not show where the gains stop.
The International Society of Sports Nutrition called 1.4 to 2.0 grams per kilo a minimum for most exercising people, and said more may be needed by people cutting calories while keeping lean mass.
So the evidence agrees that more protein helps up to about 1.6 grams per kilo. Where the benefit stops is still open.
Where the Old Number Came From
Where did the 1-gram-per-pound rule come from? Menno Henselmans, a fitness researcher, offers some plausible reasons in an article calling it a myth: people copying bodybuilders on steroids, which let you build muscle protein far more rapidly than natural trainees; old nitrogen balance studies he calls flawed; and the more-is-better habit. The nitrogen balance point cuts the other way, though: the International Society of Sports Nutrition says that method is known to systematically underestimate protein needs.
He also points to supplement companies, which have an obvious financial incentive; Grand View Research valued the global protein supplement market at nearly $30 billion in 2025 and projects growth of about 10 percent a year to 2033. And to rounding: 1 gram per pound is easy to remember. 1.62 grams per kilogram is not.
Henselmans was also co-author number five on the 49-trial meta-analysis. His article cites it, and puts his own upper figure at 1.8 grams per kilo (0.82 grams per pound).
The Debate the Number Cannot Settle
The 1.62-gram number is not as clean as it sounds. The range of uncertainty stretches from 1.03 to 2.20, and the cutoff itself did not reach statistical significance (p = 0.079).
One detailed public critique of this number, from Greg Nuckols at Stronger by Science, argues something sharp: in the studies behind it, trained lifters tended to eat more protein and gain less muscle overall than untrained ones, not because the protein stopped working, but because they had less room to grow.
Mix those two groups together and it looks like more protein stopped helping, when the real explanation may be training experience, not protein dose. Nuckols's best estimate for the break point, if one exists: around 2.0 grams per kilo, with a plausible range from 1.7 to 2.35. For men, he concludes that the old 1-gram-per-pound rule actually seems to match the research quite well; for women, he suggests targets about 10 to 15 percent lower.
So the popular target of 2.2 grams per kilo sits at the upper edge of the uncertainty, not beyond it. The Morton authors said as much themselves: because the range ran up to 2.20, they wrote that it may be prudent to recommend about 2.2 grams per kilo for those seeking to maximise gains in lean mass.
The Factor Nobody Talks About
This is where the evidence delivers its second revelation, and it restructures how the reader should think about the entire muscle-building equation.
Across the trials that tested one-rep max, the average strength gain from resistance training was 27 kilograms. Adding a protein supplement raised that by 2.49 kilograms. Run the percentages: training produced roughly 91 percent of the total strength improvement. The protein supplement added about 9 percent.
For lean mass, the proportions are different but the hierarchy is the same. Training alone built 1.1 kilograms of lean tissue. Protein supplementation added 0.30 kilograms — meaningful, statistically clear, and far from nothing. But the engine driving muscle growth was always the barbell, not the blender bottle.
The attention hierarchy that millions of lifters organise their lives around has the proportions exactly backwards. The thing most people optimise first — protein intake — is the smaller factor. The thing most people take for granted — training quality, consistency, progressive overload — is ten times more impactful for strength.
Closer Than You Think
In US national survey data covering over 5,000 adults, men ate an average of 97 grams of protein a day and women 69 grams. At 1.6 grams per kilo, an 80-kilogram lifter needs about 130 grams: 33 grams more than the men's average.
The 1-gram-per-pound target of 176 grams would take nearly double the men's average intake: a bigger change to how you eat, for a gain the evidence cannot yet confirm or rule out.
And the source matters less than the total: the evidence shows no meaningful difference between plant and animal protein for muscle when the daily grams are matched.
There is one more thing the evidence quietly delivers. Across the trials, people who added a protein supplement while lifting ended up with about 0.4 kilograms less fat and 0.3 kilograms more lean mass than people who lifted without it, and their body weight did not differ significantly.
Your Situation, Your Threshold
Here is what the evidence points to, depending on your situation.
If you lift regularly and eat at or above maintenance, the main estimate is about 1.6 grams per kilo — roughly 130 grams for an 80-kilogram person. Nuckols's reading puts it closer to 2.0, and the Morton authors suggest about 2.2 if you are aiming for the maximum.
If you are older, the daily number may need to be higher, not lower: the Morton authors note that older adults require more protein per day, and in their analysis protein supplements made no significant difference for people over 45, who were given only about 20 grams a day. The per-meal dose shifts too. In one analysis of tracer studies at rest, the single-meal dose that pushed muscle protein synthesis to its peak was about 0.24 g/kg in men around 22 and about 0.40 g/kg in men around 71 — for an 80-kilogram person, roughly 19 grams versus 32 grams.
Aiming for the higher end of the daily range with larger per-meal doses is what these findings point to. Our analysis of protein needs after 40 covers the per-meal science and the mechanism behind the shift.
If you are in a calorie deficit, the break point estimated here was never tested there: every trial behind it included only people eating at or above their energy needs. The number depends on whether you are training. If you are dieting without structured exercise, a review of 24 weight-loss trials found that diets averaging about 1.25 grams per kilo kept more fat-free mass than diets around 0.7. If you are training hard while cutting, the numbers run higher: one four-week trial in young men found that 2.4 grams per kilo during a steep deficit produced actual lean mass gain.
Our breakdown of protein during weight loss maps the deficit evidence for dieters and for hard-training cutters.
For women, the Morton authors saw no overtly apparent differences between the sexes, but on limited data: across its 49 studies, only 14 study groups were all women, and far less work has been done in women than men. The confidence is lower than it should be — and that gap in the research matters.
If your training is endurance-based rather than resistance-based, the ceiling does not drop. Measured directly in runners, the endurance-specific protein requirement landed at about 1.8 grams per kilo — within the range discussed above, with per-meal needs that may run even higher.
If you eat above the ceiling, the evidence from trained individuals suggests the excess does not become body fat. One trial had lifters consuming 4.4 grams per kilo for eight weeks — roughly triple the ceiling — with no increase in fat despite eating about 800 extra calories a day.
In healthy exercising people, eating above the ceiling does not appear harmful. Whether it builds more muscle depends on how far above: up to about 2.2 grams per kilo the evidence is not settled, and at 4.4 the trial found no significant change in lean mass. Our analysis of whether excess protein causes fat gain covers this in depth.
The Next Question the Ceiling Cannot Answer
The main estimate is about 1.6 grams per kilo a day, and its range reaches 2.2. For strength, training is the 91 percent investment.
But here is the question the ceiling does not resolve. If the daily total has an upper limit, does it matter how you spread those grams across your meals?
A controlled trial using a four-isotope tracer method found that 100 grams of protein in a single meal still produced a greater and more sustained muscle-building response than 25 grams, with no upper limit detected.
If the per-meal ceiling does not exist either, the way most people structure their protein intake might be the next rule due for correction. Which rules hold and which collapse is the question nine studies answer together — across daily targets, per-meal capacity, distribution, timing, source, aging, and three more.
For an 80 kg lifter, 1.6 g/kg is about 130 grams of protein a day, and 2.2 g/kg is about 176. In US survey data, men eat about 97 grams a day on average and women about 69. The Dietary Guidelines for Americans 2025–2030 set a goal of 1.2–1.6 grams of protein per kilogram of body weight per day for the general public.