How much protein do you really need: from the RDA to protein shakes

Protein has become the star of food labels: protein bars, “high-protein” yogurts, post-workout shakes. It all creates the impression that we’re always short of it and that more is always better. Let’s see what the research says.

Where the target comes from

Protein needs are measured by nitrogen balance: how much nitrogen a person takes in with food and how much they lose. A meta-analysis of 19 such studies with 235 participants found that the average requirement of a healthy adult is 0.65 g of good-quality protein per kilogram of body weight per day. The recommended allowance, enough for 97.5% of healthy adults, is 0.83 g/kg. Climate, age, sex and protein source made no significant difference, although women may need slightly less (Rand et al., 2003).

Target = 0.83 g × body weight (kg)
60 kg → ≈ 50 g protein a day
80 kg → ≈ 66 g protein a day

Over 65 — more

With age, the body responds less well to dietary protein, and the illnesses that become more common raise the need further. So the European PROT-AGE group advises people over 65 to get at least 1.0–1.2 g of protein per kilogram a day, active people 1.2 g/kg or more, and those with acute or chronic illness 1.2–1.5 g/kg. The exception is severe kidney disease without dialysis, when protein may need to be limited (Bauer et al., 2013). The European Society for Clinical Nutrition and Metabolism (ESPEN) gives the same figures and recommends daily physical activity — both resistance and aerobic exercise — for all older people (Deutz et al., 2014).

How much protein comes in a single meal also matters. To maximally stimulate muscle protein synthesis, men around 71 needed on average 0.40 g of protein per kilogram in one go, versus 0.24 g/kg for 22-year-olds (Moore et al., 2015). For someone weighing 70 kg, that’s about 28 g versus 17 g. A breakfast of tea and biscuits won’t provide that. That said, the PROT-AGE authors note there isn’t yet enough evidence on protein timing to make specific recommendations.

Protein and the gym

The largest meta-analysis on the subject covered 49 studies and 1,863 participants doing resistance training for at least six weeks. With protein supplements, the weight participants could lift once rose by an average of 2.49 kg more than without them, and fat-free mass — muscle, bone and water — by 0.30 kg more. The effect was smaller in older people and larger in trained ones. Most importantly, beyond about 1.6 g of protein per kilogram a day there was no further muscle gain (Morton et al., 2018). One of the authors has received funding from the US National Dairy Council — the paper says so.

What about the kidneys?

A meta-analysis of 28 studies with 1,358 healthy adults compared high-protein diets (at least 1.5 g/kg, or 20% of calories, or 100 g of protein a day) with normal ones. The change in glomerular filtration rate — the main measure of kidney function — didn’t differ between groups: in healthy people, a lot of protein doesn’t harm the kidneys (Devries et al., 2018). For people who already have kidney disease that’s not the case: their protein intake is set by a doctor.

Protein in everyday food

Be careful with grains and legumes: the pack lists protein for the dry product. 100 g of dry lentils has 24.6 g of protein, but those 100 g become about 300 g cooked, so 100 g of cooked lentils has about 8 g. Cooked buckwheat has about 3 g per 100 g. The calculator does this conversion itself if you choose the cooking method.

• 2 eggs (about 100 g) — 12.6 g of protein
• 150 g of low-fat cottage cheese — about 19 g
• 200 g of cooked buckwheat — about 6 g
• 100 g of chicken breast (raw weight) — 22.5 g
• Total — about 60 g: the daily target for a 70 kg person, with no supplements at all.

The calculator sets the protein target exactly this way: 0.83 g per kilogram of body weight, 1.2 g/kg from age 65, and 1.6 g/kg for the “gain weight” goal. The remaining calories are shared between fat and carbs. Find the richest protein sources on the Foods rich in protein page.