More protein protects muscle during weight change
High confidence
When you are deliberately losing or gaining weight, how much protein you eat changes the result. Eating about 1.6 to 2.2 grams per kilo of body weight a day helps two ways. While cutting, it helps you hold onto lean mass, the muscle you would otherwise lose along with the fat. While gaining, it helps you build more muscle. Lower intakes do both jobs less well.
Why it works
Protein works by raising how fast the body builds new muscle (muscle protein synthesis) and slowing how fast it breaks muscle down. That balance matters most when calories are low. One amino acid in protein, leucine, switches on the mTOR pathway, the signal the body uses to start building muscle.
The evidence
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This ISSN position stand reviewed diet types and body composition and concluded that a wide range of approaches, from low-fat to low-carbohydrate and ketogenic, can be similarly effective for changing body composition, since adherence and total calorie balance matter more than the specific diet. Fat loss requires a sustained calorie deficit and lean-mass gain a sustained surplus, with slower weight loss better preserving muscle in already-lean people. For lean, resistance-trained people in a calorie deficit it recommends 2.3 to 3.1 g/kg of fat-free mass per day of protein, with intakes above 3 g/kg showing promise for preserving muscle. It also found intermittent calorie restriction offered no clear body-composition advantage over daily restriction.
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This review of the contest-prep literature for drug-free bodybuilders recommends setting calories so that body weight drops about 0.5 to 1% per week, which best preserves muscle during a cut. Within that calorie level it recommends most competitors eat 2.3 to 3.1 g/kg of lean body mass per day of protein, 15 to 30% of calories from fat, and the rest of calories from carbohydrate. It also concludes that meal timing and frequency matter far less than hitting these daily totals, and that adherence over the long prep is the main driver of results.
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This literature review gives macronutrient targets for bodybuilders across both the off-season and pre-contest phases, recommending diets of roughly 55 to 60% of calories from carbohydrate, 25 to 30% from protein, and 15 to 20% from fat. It stresses keeping carbohydrate adequate (55 to 60% of energy) so training intensity holds up in both phases, and notes that eating protein/amino acids plus carbohydrate right before and after training can raise protein synthesis, refill muscle glycogen, and cut protein breakdown.
Why we call confidence high
The evidence is strong. An International Society of Sports Nutrition position stand (Aragon et al. 2017) and multiple systematic reviews agree that elevated protein intake improves body composition during both energy restriction and surplus.
Where it applies
Healthy adults
Last reviewed May 25, 2026. See how we score.