How much protein do you really need?

The evidence

The US RDA of 0.8g/kg/day was set by the Institute of Medicine (now the National Academy of Medicine) in 2005, using a meta-analysis of 58 nitrogen balance studies (Weiler et al., 2023). Researchers used 19 of the most rigorous studies to find the point where nitrogen balance hit zero. That gave an estimated average requirement (EAR) of ≈0.66g/kg/day. The RDA adds a safety margin on top, rounded to 0.8g/kg/day, designed to cover about 97-98% of healthy adults in a life stage group.

That method answers one question: how little protein avoids losing body nitrogen? It does not ask how much helps you build or keep muscle. The review itself warns that nitrogen balance studies tend to underestimate true protein needs.

For muscle, the clearest evidence is a 2018 meta-analysis of 49 trials and 1,863 people doing resistance training, with or without extra protein (Morton et al., 2018). Protein supplementation added about ≈0.30kg more lean mass and about ≈2.5kg more one-rep-max strength on average, compared with training alone. When the authors plotted daily protein intake against lean-mass gains, the benefit levelled off at about ≈1.6g/kg/day (95% CI: 1.03 to 2.20). The paper notes that the RDA of 0.8g/kg/day looks insufficient for people who want more strength and muscle from training.

The International Society of Sports Nutrition's 2017 position stand reaches a similar range: about 1.4 to 2.0g/kg/day for most people training to build or hold onto muscle, and higher, about 2.3 to 3.1g/kg/day, for people in a calorie deficit who want to protect muscle while losing fat (Jäger et al., 2017).

What it means in practice

Take someone who weighs ≈70kg (about 154 lb):

• RDA floor: 70 × 0.8 ≈ 56g/day.
• Muscle-building range from the position stand: 70 × 1.4 to 70 × 2.0 ≈ 98 to 140g/day.
• Plateau point from the 2018 meta-analysis: 70 × 1.6 ≈ 112g/day.

The floor and the range seen in training studies sit roughly double apart, for the same body weight. They answer different questions: one is about avoiding deficiency, the other is about what training studies measured.

How much people actually eat

Most US adults already eat more than the RDA. NHANES data from 2011-2014, covering 9,214 adults, found an average intake of ≈83.6g/day (Pikosky et al., 2022). Men averaged ≈98.8g/day, women ≈68.5g/day. Adults aged 19-50 averaged ≈89.0g/day, while adults 51 and older averaged less, about ≈76.5g/day.

So typical intake usually clears the RDA. Whether it clears the higher range seen in training research depends on your body weight, sex and how much you train.

Common mistakes or caveats

• Treating the RDA as a target. It is a floor built from nitrogen balance studies, a method the research itself flags as likely to underestimate real needs.
• Assuming more is always better. The 2018 meta-analysis found no extra muscle benefit above its ≈1.6g/kg/day breakpoint, and the evidence does not extend with confidence much past ≈2.2g/kg/day.
• Ignoring the age gap. NHANES shows older adults eating less protein on average, which matters because some research suggests ageing muscle responds less to a given protein dose.
• Treating this as medical advice. None of these figures are tailored to kidney disease or other conditions, which need individual guidance.

What to do instead

• If you are not training, the RDA of ≈0.8g/kg/day is a reasonable floor, and most people already clear it.
• If you do resistance training, aim nearer ≈1.4 to 2.0g/kg/day, spread across 3 to 4 meals. The position stand's own figures suggest about 0.25g/kg, or 20 to 40g, per dose.
• If you are cutting calories, lean toward the higher end of that range, since the evidence on protecting muscle during a deficit points up, not down.
• Use the protein calculator to turn these ranges into grams for your own weight, and check where foods like chicken breast or Greek yogurt fit into your day.