Both groups ate 40 percent fewer calories. Both trained six days a week. One group gained muscle. The other held every gram.
The group that ate half as much protein did not lose a gram of lean mass. In a 40 percent calorie deficit. In four weeks.
In 2016, Stuart Phillips and a team at McMaster University published one of the cleanest controlled-feeding trials in the protein-and-body-composition literature. Forty overweight young men ate 40 percent fewer calories than they burned and trained with weights and sprints six days a week for four weeks. They were randomly assigned to one of two protein intakes.
The high-protein group, eating 2.4 grams per kilogram of bodyweight each day, gained 1.2 kilograms of lean mass and lost 4.8 kilograms of fat. The lower-protein group, at half that dose, held every gram of lean mass and lost 3.5 kilograms of fat.
Two different outcomes from the same deficit, the same training programme, and the same supervised meals, separated by nothing but the protein on the plate.
What follows is everything the study found, what it did not find, and where the evidence runs out.
Protein changed the body. The barbell changed the strength. Neither did the other's job. In a 40 percent calorie deficit, doubling protein intake drove lean-mass gain and increased fat loss, while every strength measure improved equally in both groups.
- Both groups got stronger by the same amount on every measure tested — bench press, leg press, sprint power, aerobic capacity, and more. The extra protein did not buy extra strength.
- Every meal was provided. Every workout was supervised. A blood marker confirmed each group actually ate what it was assigned. This is one of the most tightly controlled feeding trials in the protein literature.
- The study isolates three levers that do different jobs: protein set the body-composition outcome, training set the performance outcome, and the deficit set the speed of fat loss.
What the Deficit Produced — and What Protein Decided
The design was severe on purpose. Every participant ate roughly 33 calories per kilogram of lean body mass per day, a 40 percent cut below maintenance. All food was provided: prepackaged meals on a rotating three-day menu, plus whey protein shakes distributed across the day, one consumed immediately after training under the investigators' watch.
Body composition was measured using a four-compartment model (combining air-displacement plethysmography, bioelectrical impedance, and dual-energy X-ray absorptiometry), which is the most rigorous assessment available in a clinical setting.
A blood marker called blood urea nitrogen, essentially a metabolic receipt for how much protein the body is processing, rose sharply in the high-protein group and stayed flat in the lower-protein group. That confirmed the two groups actually ate what they were assigned.
Then the bodies diverged.
The high-protein group gained 1.2 kilograms of lean mass while losing 4.8 kilograms of fat, building tissue while running one of the steepest calorie deficits ever tested in a controlled trial. The lower-protein group held steady: no lean mass gained, no lean mass lost, with 3.5 kilograms of fat stripped away.
Both groups ran the same deficit and trained on the same schedule. The protein dose is what separated the body-composition outcomes.
One caveat sits inside the design. The two diets matched carbohydrate at 50 percent of total energy but split fat differently: 15 percent in the high-protein group, 35 percent in the lower-protein group.
The paper's authors are direct about it: "Given that there were differences in fat content, it cannot be stated conclusively that it was protein that was responsible for the effects we report here."
They searched the literature for evidence that a fat-content difference of this size could independently drive body-composition changes and found nothing.
The most likely lever is still protein. But the lock is not perfectly clean.
Convergent evidence from the opposite energy direction tips the scale. In a surplus study, trained lifters ate 4.4 grams of protein per kilogram for eight weeks — an 800-calorie daily surplus that produced zero fat gain. Different energy state, same pattern: protein drove body composition independent of the other macronutrients.
Both groups' testosterone crashed by roughly 75 to 81 percent over four weeks — from healthy-range levels to near-clinical lows. The hormonal environment was devastated equally, and neither group's body-composition change tracked with the crash. Cortisol was the only hormone that correlated with body-composition change at all, and it explained just 16 percent of the variance in fat loss and 11 percent in lean-mass change. The other 84 to 89 percent had nothing to do with the hormones this deficit wrecked.
The Number That Was Supposed to Fail
The lower-protein group ate 1.2 grams of protein per kilogram of bodyweight per day. In most online discussions about protein during a cut, that number lives in the territory of "not enough", the range people warn will cost you muscle.
It did not cost muscle. Lean body mass changed by 0.1 kilograms over four weeks. Statistically, that is indistinguishable from zero.
Part of the explanation lives in arithmetic. These men were overweight, average bodyweight around 96 kilograms with roughly 69 kilograms of lean mass.
When protein intake is measured against total bodyweight, 1.2 grams per kilogram sounds low. But lean mass is the tissue that actually uses the protein. When the dose is recalculated against lean mass instead of total bodyweight, it lands at about 1.7 grams per kilogram of lean body mass. What sounded like a low dose on the scale was a reasonable dose for the tissue that mattered.
Six years after the trial, the study's senior author put a number on his current view. Stuart Phillips told Rhonda Patrick on the FoundMyFitness podcast in June 2022 that his optimal range for supporting muscle is 1.2 to 1.6 grams per kilogram of bodyweight [1].
He described the long-standing recommended intake of 0.8 grams per kilogram, set decades ago using nitrogen-balance methodology, as aimed at "prevention of deficiency as opposed to the optimization of processes that are important" [1].
The lower-protein arm of his own study sat at the floor of that range. That is why it held.
We're still aiming at the prevention of deficiency as opposed to the optimization of processes that are important.
What the Extra Protein Did Not Buy
Both groups got stronger. Both groups got fitter. And both groups improved by essentially the same amount.
Bench press went up. Leg press went up. Push-ups, sit-ups, sprint power, aerobic capacity, anaerobic work output, time-trial performance. Every measure the researchers tracked moved in the same direction, by the same magnitude, in both groups. The only exception was isometric knee-extension force, which did not change significantly in either group.
Across every other performance variable, the paper found no between-group difference.
The high-protein group reshaped its body. The lower-protein group preserved its body. But when it came to what the body could do (how much it could press, how fast it could sprint, how long it could sustain effort), protein intake made no measurable difference. The training stimulus drove every performance gain equally.
Protein built body composition. Lifting built strength.
That single dissociation redraws the map most people carry in their heads. The assumption that more protein automatically means more strength is not what this study found. The finding that more protein changes the shape of a body in a deficit, that is exactly what this data shows.
Protein requirements will be higher while dieting than while bulking.
The Coaches Who Already Knew
The split between protein's job and training's job was not news to everyone. Coaching educator Lyle McDonald had been telling lifters for years that "protein requirements will be higher while dieting than while bulking" [2]. That sentence captures the Longland result in ten words. It was published in an interview with Christian Finn on MuscleEvo years before the trial ran.
McDonald also noted that the body's reduced ability to retain protein on lower calories had "been known for at least 40 years" [2].
The study did not discover a principle. It formalized one.
The broader evidence runs in the same direction. A 2012 meta-analysis led by Wycherley pooled 24 randomized controlled trials with 1,063 participants [3]. Higher-protein energy-restricted diets consistently preserved more lean mass and lost more fat than standard-protein diets.
Helms, Aragon, and Fitschen published an evidence-based review in 2014 [4]. It mapped the dose-response relationship across earlier trials, reinforcing the pattern that protein dose and body-composition outcome track together during energy restriction.
Longland fits. It is not an outlier. It is the high-resolution snapshot inside a pattern that coaching and research had been circling for decades.
Where the Evidence Stops
The study tested 40 men. Young men, average age 23. Overweight men, average body mass index close to 30. Men who were physically active but had never done structured resistance training before the trial started.
The mechanism that higher protein supports lean mass during a deficit is shared biology and has been observed across other populations. The specific numbers in this paper (1.2 kilograms gained, 4.8 kilograms of fat lost, zero performance gap between groups) live inside this specific population, this specific deficit, and this specific four-week window.
The training was intense: six days a week combining a full-body resistance circuit, sprint intervals, plyometric work, and a weekly time trial. Compliance exceeded 96 percent. That level of stimulus likely contributed to the lean-mass preservation in both groups, not just the protein.
And the fat confound remains. The researchers looked for evidence that shifting dietary fat from 35 percent to 15 percent of total energy could independently produce the body-composition changes they observed. They did not find it.
But they could not rule it out, and they said so in the paper: "It cannot be stated conclusively that it was protein that was responsible for the effects we report here."
Three Levers
This study isolated three variables that do different jobs.
Protein set the body-composition outcome. The group that doubled its protein dose gained lean mass and lost more fat. The group that ate less protein held its lean mass and still lost meaningful fat. The dose changed the shape, not the function.
Training set the performance outcome. Every strength and fitness measure improved equally in both groups, regardless of protein intake. The barbell, the sprints, and the circuits drove what the body could do.
The size of the deficit set the speed. Both groups ran a 40 percent cut and both lost substantial fat mass in four weeks. The deficit was the engine of fat loss. Protein decided what came along with it.
Three levers. Three jobs. The question is not whether to eat protein during a cut. The question is which outcome matters most right now, and which lever to pull harder.
This study drew three lines.
Line one: the protein floor. The group eating 1.2 grams per kilogram of bodyweight held every gram of lean mass during a 40 percent deficit. If protecting muscle during a cut is the goal, the floor from this data is lower than most internet advice suggests — provided training is intense and consistent.
Line two: the recomp threshold. The group eating 2.4 grams per kilogram gained lean mass while losing fat. If body recomposition is the goal, this study found it required doubling the floor dose — not a small nudge upward.
Line three: the training split. Strength improved equally regardless of protein dose. The training programme drove every performance gain. If getting stronger is the priority, protein dose is not the lever this data points to.
What other research found
What this means for you
These men had never lifted weights in a structured programme before. That means the lean-mass gains in both groups included a substantial contribution from what the fitness world calls beginner response — the rapid adaptation that comes with a first exposure to resistance training.
For someone who has been lifting for years, that beginner contribution is gone. The lower-protein group's lean-mass preservation at 1.2 grams per kilogram may have been partly powered by that novelty stimulus, not just the protein.
There is also the per-meal dose. The high-protein group consumed roughly 49 grams per meal. Trained muscle tissue may need a stronger per-meal signal to trigger building because it has already adapted to the baseline stimulus. The doses that worked for untrained men may not be the same doses that work for you.
Forty men. Zero women. The study's authors themselves cite Josse et al. 2011 — a trial in overweight and obese premenopausal women — as running in the same direction. The principle that higher protein supports lean mass during a deficit is shared biology and has been observed in female populations.
But the specific numbers belong to these 40 men. Women typically carry less lean mass, operate in a different hormonal environment, and may respond to different absolute protein targets. The direction of the finding likely travels. The gram targets from this particular trial may not.
The average age in this study was 23. At that age, muscle tissue responds readily to both protein and training — a sensitivity that declines with time. The phenomenon is called anabolic resistance: the same protein signal produces a smaller building response in older tissue.
The lower-protein group's lean-mass preservation at 1.2 grams per kilogram of bodyweight relied partly on that youthful sensitivity. For someone over 40, the same dose may fall short of what the tissue needs to hold steady during a deficit.
The per-meal dose matters more with age. The study's high-protein group averaged roughly 49 grams per meal — a threshold that may need to rise, not fall, as the muscle's ability to respond to protein declines with age. The floor that held for 23-year-olds may not be your floor.
Before you change anything
Forty young men, average age 23, all overweight with a body mass index near 30, none with prior resistance-training experience. All from the Hamilton, Ontario area. All consumed provided meals with whey protein shakes, one taken immediately after training under the investigators' watch.
The training was intense: six days a week of supervised resistance circuits, sprint intervals, plyometrics, and time trials. Exercise compliance exceeded 96 percent.
No women were tested. No older adults. No trained athletes. No one on a moderate deficit. The protein source was exclusively whey isolate. The deficit was 40 percent — roughly double the typical dieting cut of 15 to 25 percent.
The study ran for 28 days. Whether the lean-mass gain in the high-protein group would continue, plateau, or reverse over a longer period is unknown from this data.
The two diets matched carbohydrate but split fat differently: 15 percent of total calories from fat in the high-protein group versus 35 percent in the lower-protein group. The study's authors are direct about this: they cannot state conclusively that protein alone drove the body-composition differences. They searched for evidence that the fat difference could explain the results and found none, but the confound remains open.
With 20 men per group, the study was powered to detect a one-kilogram lean-mass difference but may have missed smaller between-group differences in performance variables.
This is a single, well-designed randomized controlled trial with 40 participants. The controlled-feeding protocol, four-compartment body-composition measurement, objective compliance marker, and blinded analyses place it at the rigorous end of body-composition research.
The body-composition direction — higher protein preserves or builds more lean mass during a deficit — runs in the same direction as a meta-analysis of 24 randomized trials with 1,063 participants and four decades of coaching practice. The direction is well-supported. The specific magnitude of the effect is from one study of 40 men.
The strength-dissociation finding — that protein dose changed body composition without changing performance — has less external replication as a standalone result. It is consistent with the broader evidence that training drives strength independently of protein dose, but few studies have isolated the comparison as cleanly as Longland did.
During a deficit, 2.4 g/kg preserved muscle and built strength. When the deficit ends and the goal becomes growth, the protein target shifts.
Morton's 2018 meta-analysis pooled 49 studies to find exactly where that growth ceiling sits — and the gap between it and what most lifters consume is smaller than the supplement industry suggests. The deficit dose, the growth ceiling, the aging shift — where each threshold sits relative to the others is what turns individual study numbers into a coherent plan.
What This Study Found
All findings from this paper, in plain language.
- Men eating the higher protein dose gained 1.2 kilograms of lean mass in a severe calorie deficit, while men eating half as much protein gained essentially none.
- The higher-protein group lost 4.8 kilograms of fat, about 37 percent more than the lower-protein group's 3.5 kilograms.
- The lower-protein group at 1.2 grams per kilogram held every gram of lean mass during four weeks of a 40 percent deficit combined with intense training.
- Every strength and fitness measure improved equally in both groups — protein dose changed the body's shape but not what it could do.
- Cortisol was the only hormone correlated with body-composition change, and it explained less than a fifth of the variance — most of what happened had nothing to do with cortisol.
- Testosterone crashed by roughly 75 to 81 percent in both groups and showed no relationship to whether men gained or lost lean mass.
- A blood marker called BUN rose sharply in the high-protein group and stayed flat in the other, confirming each group actually ate what it was assigned.
- Kidney function markers stayed within normal range in both groups throughout the study, including at the higher protein dose.
- The high-protein group averaged roughly 49 grams of protein per meal, repeatedly hitting the threshold the authors say maximally stimulates muscle building — the lower-protein group fell short of it.
- The two diets also differed in fat content — 15 percent versus 35 percent of calories — so the body-composition results cannot be attributed to protein alone.