The One Macro Most People Under-Eat on Purpose

Protein is the most consistently under-discussed lever in everyday nutrition advice.

How much you actually need

The official Dietary Reference Intake for protein (also called the RDA) — 0.8 g per kilogram of bodyweight per day — is set to prevent deficiency in a sedentary population, not to optimise body composition or support training[10]. For anyone resistance training, or anyone in a calorie deficit, the evidence supports a considerably higher target. A widely cited review found that muscle gain from resistance training plateaus at around 1.6 g/kg/day — going higher adds no measurable benefit on average[9].

Why more protein helps body composition specifically

Adequate protein is what lets resistance training actually build or preserve muscle, rather than just providing a stimulus with nothing to build it from — and three separate mechanisms explain its outsized effect on body composition relative to its calorie content. First, protein supplies the amino acids — particularly leucine, the specific amino acid that most directly triggers muscle-building — needed to stimulate muscle protein synthesis[9][13]. Second, protein has a higher thermic effect of food (the energy your body spends digesting food itself) than carbohydrate or fat — roughly 20–30% of its calories are spent on digestion and processing, compared with 5–10% for the other two macronutrients. Third, protein is consistently the most satiating macronutrient gram-for-gram, which helps with adherence to a calorie target[12].

Protein quality and distribution

Not all protein sources are equal. Animal proteins (meat, fish, eggs, dairy) and soy are described as "complete," containing all nine essential amino acids in roughly the proportions the body needs. Most plant proteins are lower in one or more essential amino acids (commonly lysine in grains, or methionine in legumes), which is easily solved by eating a varied mix of plant sources across the day rather than requiring any single food to be complete on its own.

Evidence also supports spreading protein intake across multiple meals rather than concentrating it in one. A muscle protein synthesis response appears to plateau at roughly 0.4 g/kg of bodyweight per meal, suggesting that 3–4 meals containing 25–40 g of protein each make more efficient use of total intake than one or two very large servings[14].

Is high protein intake harmful to the kidneys or bones?

This claim originated from studies of people with pre-existing kidney disease, where protein restriction is genuinely indicated, and was then generalised — incorrectly — to healthy populations. In people with normal kidney function, intakes well above the RDA show no evidence of harm in controlled studies[15]. Concerns about bone loss from protein-induced acid load have also not held up; higher protein intake is associated with better, not worse, bone mineral density in most studies, likely because protein supports the collagen matrix of bone alongside calcium.