More protein protects muscle during weight change

When you are deliberately losing or gaining weight, how much protein you eat changes the result. While cutting, eating more than the basic 0.8 grams per kilo of body weight helps you hold onto lean mass, the muscle you would otherwise lose along with the fat. While building with resistance training, about 1.6 grams per kilo a day captures most of the extra muscle, and up to about 2.2 grams covers people who respond best. The benefit shows up when you are dieting or training, not when you are doing neither.

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

• Aragon, A.A., Schoenfeld, B.J., Wildman, R. et al. (2017). International Society of Sports Nutrition Position Stand: Diets and Body Composition. Journal of the International Society of Sports Nutrition.

  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, and that long-term success depends on compliance (adherence). 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.

• Hudson, J. L., Wang, Y., Bergia, R. E., III et al. (2020). Protein Intake Greater than the RDA Differentially Influences Whole-Body Lean Mass Responses to Purposeful Catabolic and Anabolic Stressors: A Systematic Review and Meta-analysis. Advances in Nutrition.

  Overall, protein intakes above the RDA improved lean-mass change compared with the RDA. Higher protein reduced lean-mass loss during energy restriction and increased lean-mass gain with resistance training, but made no difference in adults who were neither dieting nor training.

• Morton, R. W., Murphy, K. T., McKellar, S. R. et al. (2018). 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. British Journal of Sports Medicine.

  Protein supplementation significantly increased resistance-training gains in strength and fat-free mass. The benefit shrank with age and was larger in resistance-trained people. Gains in fat-free mass plateaued at a total protein intake of about 1.62 g/kg/day (95% CI 1.03 to 2.20), and the authors suggest about 2.2 g/kg/day for those seeking to maximise gains.

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Why we call confidence high

Two meta-analyses of randomized trials carry this. Hudson (2020; 18 RCTs) found protein above the RDA reduced lean-mass loss during energy restriction (0.36 kg) and increased lean-mass gain with resistance training. Morton (2018; 49 RCTs, 1,863 adults) found protein supplementation boosted resistance-training gains in muscle mass and strength, with gains plateauing around 1.62 g/kg/day (95% CI 1.03-2.20). The International Society of Sports Nutrition position stand (Aragon 2017) agrees higher protein may improve body composition and suggests more (2.3-3.1 g/kg of fat-free mass) for lean, resistance-trained people who are dieting.

Where it applies

Healthy adults during purposeful weight change. The 1.6-2.2 g/kg figure comes from resistance-training trials; lean, resistance-trained dieters may need more.