Protein
The macronutrient made of amino acids, used to build and repair tissue.
Protein is the macronutrient built from amino acids, the twenty building blocks your body uses to make muscle, tendon, skin, hair, enzymes, antibodies and most of the machinery that keeps you running. Nine of those amino acids are essential, meaning your body cannot make them and food has to supply them.
It matters more than the other two macronutrients per gram eaten, for three reasons. It is the only one that supplies the raw material for tissue. It is the most filling, so a higher protein diet tends to reduce intake without anyone counting. And it is the most protected during weight loss: eat enough and the weight you lose skews towards fat rather than muscle.
How much is a solved question for practical purposes. Pooling 49 trials in 1,863 people, protein supplementation improved gains in fat free mass and strength during resistance training, and the benefit stopped once total intake passed roughly 1.6 g per kg of bodyweight a day. Somewhere between 1.6 and 2.2 g per kg covers almost everyone training for muscle.
Quality varies, and the differences are smaller than marketing implies. Animal sources are complete and rich in leucine, the amino acid that most strongly triggers muscle protein synthesis. Plant sources are individually lower in one or another essential amino acid, which matters at low total intakes and largely disappears when you eat a varied diet with enough protein in it.
Distribution is fine tuning rather than the main event. Roughly 0.4 g per kg per meal across at least four meals is a sensible pattern, because the muscle building response to a single sitting saturates. Total daily intake still does most of the work, and the anabolic window is far wider than the supplement industry once claimed.
Older adults need more, not less. Muscle becomes less responsive to protein with age, so the PROT-AGE group recommends healthy older people start at 1.0 to 1.2 g per kg a day, paired with resistance training rather than offered instead of it.
In practice, set the target first with our protein intake calculator, then build meals around it. Whole food does the job; powder is convenience, not magic.
Sources
- Morton RW, 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. Br J Sports Med 2018;52:376-384
- Schoenfeld BJ, Aragon AA. How much protein can the body use in a single meal for muscle-building? J Int Soc Sports Nutr 2018;15:10
- Bauer J, et al. Evidence-based recommendations for optimal dietary protein intake in older people: PROT-AGE. J Am Med Dir Assoc 2013;14:542-559