7.4.1: Protein: The Building Block

Protein is the only macronutrient that directly supplies the amino acids needed to build and repair muscle tissue. When you eat protein, your digestive system breaks it down into individual amino acids, which are then absorbed into the bloodstream and delivered to muscle cells. There, the mTORC1 pathway (Chapter 1) uses these amino acids—especially leucine—as raw materials to synthesize new contractile proteins (actin and myosin). Without adequate protein, the growth signal from training has nothing to build with.

How much do you need?

The most comprehensive meta-analysis on protein intake and muscle gain, by Morton et al. (2018), analysed 49 studies and found that protein supplementation significantly increased gains in fat-free mass during resistance training, with a breakpoint at approximately 1.6 g/kg/day—meaning that intakes above this threshold provided diminishing returns for most people [4]. However, the 95% confidence interval extended up to 2.2 g/kg/day, and individual variability is real.

Practical recommendation: aim for 1.6–2.2 g/kg of bodyweight per day. Use the lower end during a surplus or maintenance, and the higher end during a caloric deficit, when protein becomes even more critical for preserving muscle mass, maintaining satiety, and taking advantage of protein’s high thermic effect.

Distribution matters somewhat. Spreading protein across 3–5 meals with at least 0.3 g/kg per meal (~25–40 g for most people) ensures a consistent supply of amino acids and keeps muscle protein synthesis (MPS) elevated throughout the day [5]. This doesn’t mean eating 6 meals a day is mandatory—3–4 protein-rich meals is sufficient for the vast majority of people.

Practical sources: Chicken, turkey, beef, fish, eggs, dairy (Greek yogurt, cottage cheese, whey), legumes (lentils, chickpeas), tofu, tempeh. Protein powder (whey, casein, or plant-based) is a convenient option when whole food is impractical, but it is not inherently superior to food.