Protein

The official RDA is 0.8 g per kg of body weight (0.36 g per lb) for sedentary adults — about 56 g for a 70 kg (154 lb) adult — but Harvard Health and most recent research describe this as the minimum to prevent deficiency, not the optimal target. Typical evidence-based targets: 1.0–1.2 g/kg (0.45–0.55 g/lb) for healthy adults, 1.2–1.6 g/kg (0.55–0.73 g/lb) for regular exercisers, up to 2.0 g/kg (0.9 g/lb) for athletes actively building muscle, and 1.0–1.2 g/kg (0.45–0.55 g/lb) for adults over 65 to offset age-related muscle loss. Pregnancy raises requirements to roughly 1.1 g/kg (0.5 g/lb), with further increase in the third trimester. The FDA Daily Value used on nutrition labels is 50 g/day.

Ranked by grams of protein per 100 g (3.5 oz) of food: seitan (wheat gluten, ~75 g), dried soybeans (~36 g), hemp seeds (~31 g), pumpkin seeds (~30 g), peanuts (~26 g), canned tuna (~26 g), chicken breast (~31 g cooked), beef (~26 g cooked), hard cheeses like parmesan (~36 g), dried lentils (~25 g), almonds (~21 g), Greek yogurt (~10 g), eggs (~13 g / about 6 g per large egg), tempeh (~19 g), firm tofu (~8–17 g), and cooked oats (~2.5 g — higher dry). For rankings by actual serving size rather than per-100 g density, see the full top-foods ranking with USDA-verified amounts.

Hitting 100 g is straightforward once you spread protein across 3–4 meals. An example day providing ~100 g: breakfast — 1 cup (240 mL) Greek yogurt or soy yogurt (~15–20 g) + 30 g (1 oz) almonds (~6 g); lunch — 1 cup (200 g / 7 oz) cooked lentils or 150 g (5 oz) chicken breast (~25–45 g) with vegetables; snack — 1 scoop protein powder or 2 hard-boiled eggs (~15–25 g); dinner — 170 g (6 oz) salmon, 200 g (7 oz) tofu, or 1 cup beans with rice (~25–40 g). Adjust portions to match your target. Two principles matter more than food choice: aim for 20–40 g of protein per meal, and distribute evenly — research shows even distribution boosts 24-hour muscle protein synthesis by ~25% vs. loading most protein at dinner.

For hypertrophy (muscle growth) combined with resistance training, meta-analyses consistently point to 1.6 g/kg (0.73 g/lb) as the intake above which additional protein stops producing additional muscle gain in most adults — see the landmark Morton et al. 2018 meta-analysis (British Journal of Sports Medicine). Competitive athletes in active muscle-building phases sometimes go to 2.0–2.2 g/kg (0.9–1.0 g/lb), but marginal returns diminish above 1.6 g/kg. The biggest practical levers are: train progressively, eat enough calories, distribute protein across 3–4 meals with ~0.4 g/kg (0.18 g/lb) per meal (roughly 20–40 g), and include a protein-containing meal within a few hours of training. Protein quality matters less than total daily intake once you are in this range — a varied diet that hits the total will build muscle regardless of whether the sources are plant, animal, or mixed.

Clinical deficiency (kwashiorkor with oedema and liver enlargement, or marasmus with severe wasting) is rare in countries with stable food supplies. Subclinical inadequacy is more common and shows up as: gradual muscle loss (especially after 60), slowed wound healing, thinning hair and brittle nails, weakened immune response (more frequent or longer-lasting infections), persistent fatigue, and in some people swelling in the feet or ankles. In children, inadequacy causes stunted growth and cognitive impairment. The highest-risk groups are adults over 70 (up to 46% consume below the 0.8 g/kg RDA per Bauer et al. 2013), people recovering from surgery or serious illness, very low-calorie dieters, and people on restrictive diets without planning.

For people with healthy kidneys, the evidence does not support the popular claim that high protein intake damages kidney function. Systematic reviews of high-protein diets in healthy adults have not shown harmful effects on kidney markers. However, long-term intakes above about 3.5 g/kg (1.6 g/lb) provide no added benefit and may place unnecessary metabolic stress on the kidneys, and there is no Tolerable Upper Intake Level (UL) established for protein. The important exception: people with pre-existing chronic kidney disease (CKD) are often medically advised to restrict protein to reduce load on damaged nephrons — if you have or suspect CKD, diabetes-related kidney changes, or a single kidney, consult a healthcare provider before increasing protein intake. Signs people sometimes attribute to excess intake (dehydration, digestive discomfort, bad breath from ketosis) usually reflect low carb or low fluid intake rather than protein itself.

Yes, and strongly. After about age 50 the body becomes progressively less efficient at using dietary protein to build and maintain muscle — a phenomenon called anabolic resistance. To overcome it, the expert consensus from the PROT-AGE Study Group (Bauer et al. 2013, JAMDA) recommends 1.0–1.2 g/kg/day (0.45–0.55 g/lb) for healthy older adults and 1.2–1.5 g/kg (0.55–0.68 g/lb) for those with acute or chronic illness or existing muscle loss. Three elements matter together: (1) hit the daily total; (2) distribute across meals — ~25–30 g protein per meal clears the anabolic threshold better than loading protein at dinner; (3) pair protein intake with resistance (strength) training 2–3 times per week. Combined, this is the best-established strategy to preserve muscle mass, strength, and independence in later life.

The standard quality measure is the Digestible Indispensable Amino Acid Score (DIAAS) — a ratio of digestible essential amino acids in a food to the FAO reference pattern, where 1.0 means the food meets 100% of essential amino acid needs per gram of protein. Single foods: milk (1.22), egg (1.19), chicken (1.08), and soy protein isolate (0.98) are all at or near "excellent"; pea protein (0.82) is "good"; rice (~0.69) and wheat (~0.43) are lower because each is limited by a specific amino acid. Combinations: foods with opposite limiting amino acids cover each other — for example, a plate of about 100 g (3.5 oz) cooked rice with 87 g (3 oz) cooked lentils gives a computed DIAAS of ~1.06, matching animal proteins. A 2022 Journal of Nutrition study (Rafii et al.) confirmed that combining rice and lentils improves methionine availability versus lentils alone. Critically, complementary foods do not need to be eaten at the same meal: the body maintains a circulating amino acid pool that is replenished across meals throughout the day (Young & Pellett 1994, Am J Clin Nutr; Academy of Nutrition and Dietetics 2016). Bottom line: at the food level, several animal proteins score higher than most single plant proteins; at the diet level, a varied plant-based diet readily delivers equivalent protein quality to an animal-based diet.