Protein is the most discussed and least problematic nutrient in plant-based eating. The requirement is smaller than marketing suggests, and the plant sources that cover it are ordinary supermarket food.
The requirement in plain figures
The reference intake for a sedentary adult is 0.8 g per kilogram of body weight per day — about 56 g for a 70 kg person. Older adults benefit from 1.0–1.2 g/kg to counter age-related muscle loss. People doing regular resistance training see benefit up to roughly 1.6 g/kg, with little additional gain above 2.0 g/kg in controlled trials. Plant-based eaters are often advised to add about 10% to account for slightly lower digestibility, which moves a 70 kg sedentary adult to around 62 g.
Digestibility and amino acids
Plant proteins score slightly lower on digestibility measures such as DIAAS, and individual foods vary in their limiting amino acid: legumes are lower in methionine, grains lower in lysine. Eating both across a day, which almost everyone does without trying, resolves this completely. The 1970s advice to combine proteins at each meal was withdrawn by its own author; the body maintains an amino-acid pool across many hours.
Leucine and muscle building
For anyone training seriously, leucine is the amino acid worth tracking, since it triggers muscle protein synthesis. Soy, lentils, peanuts, seitan and pea protein are the strongest plant sources. A practical rule is 2.5–3 g of leucine per meal, achieved by roughly 30–40 g of plant protein in one sitting — around 200 g of tofu, or 150 g of tempeh, or a large lentil portion with a grain.
The real-world failure mode
People who fall short almost never do so because plants lack protein. They fall short because they cut animal products and replaced them with salad, fruit and refined carbohydrate rather than with legumes, soy, seitan, nuts and seeds. Protein density, not protein quality, is what needs attention when planning.
