Walk into any gym and ask how much protein it takes to build muscle, and you will hear numbers ranging from "a normal diet is fine" to "a gram per pound, minimum." Few nutrition questions generate more confident answers on less agreement. This article will dive into a recent commentary from Dr. Stuart Phillips, a professor of kinesiology at McMaster University and one of the most widely cited researchers in the protein field(1).
His conclusion is clear. For people who do resistance training, a daily intake of about 1.6 grams of protein per kilogram of body weight is sufficient, whether the goal is losing fat, gaining muscle, or both. That works out to roughly 0.7 grams per pound, or about 130 grams a day for a 180-pound adult.
Phillips is not arguing that more protein is harmful, his point is narrower and more interesting. No study has convincingly shown that eating more than this builds more muscle. He puts it like this: "Lifting bakes the cake. Protein adds a very thin layer of icing." It is absolutely clear from the evidence over decades that the major catalyst to strength and skeletal muscle growth is resistance training
The 1.6 g/kg/day figure traces back to a 2018 meta-analysis, a study that pools results from many smaller trials, which Phillips co-authored(2). Across 49 trials, the added benefit of protein supplementation on top of resistance training appeared to level off at around 1.6 g/kg/day. The number spread quickly, and Phillips later described it on social media as "the ceiling."
Most protein studies do not measure muscle at all. They measure "lean mass" or "fat-free mass," usually with a DXA scan, a low-dose X-ray that divides the body into fat, bone, and everything else. That "everything else" includes muscle, but also organs, skin, blood, connective tissue, water, and the contents of the digestive tract.
Think of it as weighing a packed suitcase and reporting the result as the weight of your clothes. The clothes are in there, but so are the shoes, the toiletry bag, and the laptop.
The size of the gap is striking. In one study, researchers measured young women with several methods on the same morning, including D3-creatine dilution, a technique that estimates muscle directly by tracking a labeled form of creatine, a compound stored almost entirely in skeletal muscle(3).
DXA reported an average of 41.6 kilograms of lean mass. Actual muscle came to about 21.5 kilograms. Roughly half of what the scanner labeled "lean" was something other than muscle. (see figure below) Research in nearly 1,400 older men found a similar pattern, and directly measured muscle predicted strength, falls, and mobility far better than DXA lean mass did.
Figure 1. Lean mass, fat-free mass and skeletal muscle mass in the same 21 women on the same morning (group means). Blue is skeletal muscle by D3-creatine dilution (about 21.5 kg, taken as mean lean mass minus mean bias). Orange is everything else that each method counted as lean or fat-free mass. Data from Tables 1 and 2 of D’Souza et al.
Lean mass also shifts for reasons unrelated to muscle growth. When trained cyclists loaded up on carbohydrates for 48 hours, their DXA lean mass rose by about 2%, and by about 3% when creatine was added(4). No one builds that much muscle in two days. What changed was the water and stored carbohydrate held inside the tissue. In other studies, much of an apparent lean-mass gain turned out to be extra fluid, and volunteers who were simply overfed for eight weeks without exercising gained about 3 kilograms of lean mass, very little of which was likely muscle.
This matters because the debate over protein often turns on differences of a few hundred grams of lean mass between groups. On a measure this noisy, a difference that small cannot be confidently attributed to muscle. Dr. Phillips is candid that the criticism applies to his own work as well, since the 1.6g/kg/day figure was also derived from lean mass. But that weakness does not strengthen the case for higher intakes. It leaves even less evidence that extra protein produces extra muscle.
Suppose we set the measurement problem aside and treat lean mass as muscle. How much does additional protein contribute?
In the 2018 analysis, resistance training alone added about 1.1 kilograms of lean mass over roughly three months, and protein supplementation added another 0.3 kilograms(2). Using estimates from a larger 2022 analysis of 74 trials, raising intake from 1.6 to 2.2 g/kg/day would add about 200 grams of lean mass, roughly the weight of a smartphone, and perhaps half of it would not be muscle.
The most direct test came from a 16-week trial in resistance-trained men assigned to either 1.6 or 3.2 g/kg/day, double the protein(5).
Lean mass rose by 3.5% in the first group and 4% in the second, a difference that was not statistically meaningful. Strength improved equally in both. A separate analysis found that gains in strength stopped responding to protein at about 1.5 g/kg/day, which may be the most practical signal of where functional benefits taper off.
Building muscle requires less raw material than most people assume
To show how little protein new muscle actually contains, Phillips works through a deliberately extreme scenario: an 80-kilogram (176-pound) man who adds 20 kilograms of pure muscle in a single year, a rate far beyond what is naturally achievable.
Muscle is about 75 to 80% water, and only around a quarter of it is protein. Twenty kilograms of muscle therefore contains about 5 kilograms of protein. Spread across a year, that is 13.7 grams a day, roughly the amount in two eggs. Even after adding generous allowances for protein used first by the gut and liver, the total stays within ordinary recommendations in most scenarios.
A useful way to picture this is a brick wall under construction. Protein supplies the bricks, and those are rarely in short supply for anyone eating a reasonable diet. What sets the pace is the bricklayer, which is to say your training. Stacking more bricks in the yard does not make the wall go up faster.
Part of the reason is that muscle is remarkably good at reusing its own material. It is continuously broken down and rebuilt, and a man of this size turns over about 100 grams of muscle protein every day. Much of the raw material is recycled from within the muscle itself. Growth is simply the small difference between what is built and what is broken down.
Resistance exercise makes this process more efficient.
In a classic study, a single workout more than doubled the rate of muscle protein synthesis, even in people who had not eaten, and reduced net protein loss for up to two days afterward(6).
If moderate amounts of protein already maximize muscle building after a meal, what happens to the rest?
Some researchers argue that surplus protein is held in a short-term reserve, mainly in the gut, and gradually released to muscle. In one carefully conducted study, a single 100-gram dose of protein after exercise kept muscle-building activity elevated for up to 12 hours, longer than a 25-gram dose did(7). Phillips does not dispute those findings. His question is whether they add up to more muscle over weeks and months, and to his knowledge no study has shown that they do.
The body has no dedicated storage depot for protein, unlike the way it stores fat or carbohydrate. When intake exceeds what tissues can use, the excess amino acids are broken down. Some are burned for energy, some are converted to glucose, and the leftover nitrogen is excreted in urine as urea. Studies consistently show that as protein intake rises beyond what muscle can use, amino acid burning and urea production rise along with it.
"The 2018 study itself suggested 2.2 g/kg/day might be prudent." Phillips concedes that the line was a hedge he would not write today. The study's best estimate was 1.62 g/kg/day, with a confidence interval, the range within which the true value plausibly lies, running from 1.03 to 2.20(2).
Recommending the top of that range expresses a preference for more protein. It is not evidence that more is effective, any more than the bottom of the range is evidence that 1.03 is enough.
A frequently cited study from Phillips's own laboratory compared 1.2 and 2.4 g/kg/day during an aggressive diet, and the higher intake performed better. But that trial never tested 1.6, so it cannot show where the benefit begins. When studies have compared 1.6 directly with higher intakes during energy restriction, they have found no meaningful additional benefit for lean mass.1 One short study in lean, trained men did find that those eating 1.6 g/kg/day reported more fatigue and stress than those eating 2.8. Feeling better during a hard diet may be a perfectly good reason to eat more protein, Phillips notes. It is simply a different reason than building muscle.
These estimates come from a method called indicator amino acid oxidation (IAAO), which tracks how the whole body uses protein over a single study day. Muscle accounts for only about a quarter of whole-body protein synthesis, the studies involved seven or eight participants each, and the protein was given in small hourly portions of liquid amino acids. Even researchers who use the method have cautioned that its results should not be read as protein requirements.
People do vary. But much of what looks like individual variation in study results is measurement error and ordinary day-to-day fluctuation. No trial has shown that people who gain little on 1.6 g/kg/day would gain more on 2.4, and the 1.6 figure already includes a margin of safety.
This is an example of confusing correlation with cause. In a survey of natural bodybuilders, those who placed in the top five and those who did not ate similar amounts of protein, between 2.7 and 3.3 g/kg/day(1). The only nutrient that clearly differed was carbohydrate. Phillips adds a useful reminder that the post-workout "anabolic window" was treated as settled gym wisdom for years before research showed little evidence for it.
A position stand from the International Society of Sports Nutrition recommends higher intakes for female athletes, up to 1.8 to 2.2 g/kg/day, with further increases during the luteal phase (the second half of the menstrual cycle, after ovulation) and after menopause. Phillips examined the sources behind those recommendations and found the support thin.
The position stand itself acknowledges that no studies have directly tested protein requirements across the menstrual cycle. Studies that measured muscle protein synthesis in both halves of the cycle found no difference(8).
When women and men are tested in the same study, their estimated protein needs are similar, and with equivalent training, both sexes gain comparable amounts of muscle relative to their size. Because women carry a somewhat smaller share of their body weight as muscle, about 31% compared with 38% in men, their protein needs for muscle building per kilogram may, if anything, be slightly lower.
The evidence on menopause is similarly limited. Much of the difference in muscle between pre- and postmenopausal women reflects the roughly 10-year age gap between the groups rather than menopause itself. Muscle continues to respond well to training after menopause, and no trial has tested the recommended intakes of 1.8 g/kg/day or more in postmenopausal women. Phillips agrees that women have been understudied. But in his view, recommending higher intakes requires evidence that they help, and that evidence does not yet exist.
None of this is an argument for the current Recommended Dietary Allowance of 0.8 g/kg/day, which is likely too low for many people. Older adults have good reasons to eat more. Aging muscle needs a larger dose of protein per meal to produce the same building response, and older adults in the highest fifth of protein intake lose about 40 percent less lean mass over three years than those in the lowest. Higher intake has also been associated with lower frailty risk in older women. The research supports 1.2 to 1.6 g/kg/day for older adults, with little evidence for benefits above that.
According to Phillips, everyone in this argument is working with evidence that is weak in the same places. Studies measure lean mass rather than muscle. Most head-to-head trials are small, often 11 to 14 participants per group, and short, lasting 2 to 16 weeks, which makes small effects nearly impossible to detect reliably. Phillips acknowledges that this limitation cuts against his own position, too. Failing to find a benefit is not the same as proving none exists. Most participants also report their own diets rather than eating food supplied by researchers, many analyses compare averages across very different studies, and short laboratory measurements cannot show whether muscle actually grew over months.
He also describes what would settle the question: a single well-designed trial in experienced lifters comparing 1.6 g/kg/day with a higher intake, with food provided or rigorously tracked, around 50 participants per group including women, and an outcome that measures muscle directly, using MRI or D3-creatine dilution rather than lean mass.
The practical message is reassuring. If you lift consistently and reach about 1.6 grams of protein per kilogram of body weight each day, you are already capturing nearly all of the muscle-building benefit protein can offer. Going higher is generally considered safe for healthy adults and may make a hard diet feel more manageable, but it has not been shown to build more muscle. Training does most of the work.
Protein makes sure that work is not wasted.
For the lifter in their mid-20s to mid-40s balancing training with a career, family, and a grocery budget, the challenge is rarely knowing the target. It is hitting it every day. As a scientist, I find this research clarifying, because it shifts the goal from chasing extreme numbers to meeting a sensible daily amount consistently.
A single 20-gram scoop of Steel's WHEY-PRO, WHEY-ISO, or VEG-PRO covers about a sixth of a 180-pound lifter's daily target. Combined with three protein-rich meals, a shake closes the gap reliably.
WHEY-ISO is the natural fit during a cut, when its extra filtration delivers more protein for fewer calories and a higher intake may help you feel better through the deficit. WHEY-PRO is a strong everyday option, and VEG-PRO offers a dairy-free blend of pea and brown rice protein. Steel's recent price reductions on all three matter more than they might seem. The evidence says the benefit comes from consistency, not from megadoses, and consistency is much easier to sustain when the product fits your budget. Spend less on extra protein you do not need, and put the effort into the training that actually builds the muscle.
As whey protein prices have risen, STEEL has lowered their everyday price to remain the lowest in the country so you can get the nutrition you need at a price you that works for you.
References:
1. Phillips SM: Show me the muscle: How much can protein really add to exercise gains? SportRxiv, 2026 (preprint, not peer reviewed)
2. Morton RW, Murphy KT, McKellar SR, et al: A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med 52:376-384, 2018
3. D'Souza AC, Rajmohan S, Younes R, et al: Application of the COSIAM method for muscle protein turnover and skeletal muscle mass in young females: A comparison of methods for body composition assessment. Adv Exerc Health Sci 1:248-259, 2024
4. Bone JL, Ross ML, Tomcik KA, et al: Manipulation of muscle creatine and glycogen changes dual x-ray absorptiometry estimates of body composition. Med Sci Sports Exerc 49:1029-1035, 2017
5. Bagheri R, Kargarfard M, Sadeghi R, et al: Effects of 16 weeks of two different high-protein diets with either resistance or concurrent training on body composition, muscular strength and performance, and markers of liver and kidney function in resistance-trained males. J Int Soc Sports Nutr 20:2236053, 2023
6. Phillips SM, Tipton KD, Aarsland A, et al: Mixed muscle protein synthesis and breakdown after resistance exercise in humans. Am J Physiol 273:E99-E107, 1997
7. Trommelen J, van Lieshout GAA, Nyakayiru J, et al: The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med 4:101324, 2023
8. Colenso-Semple LM, McKendry J, Lim C, et al: Menstrual cycle phase does not influence muscle protein synthesis or whole-body myofibrillar proteolysis in response to resistance exercise. J Physiol 603:1109-1121, 2025
