You need far more protein than the RDA

Trials that raised protein intake above the RDA of 0.8 g per kg of body weight per day have mostly found small extra gains in lean mass and strength, and mainly in people doing resistance training. A 2022 pooled analysis of 74 randomized trials found a small added lean mass effect in people doing resistance exercise, and a separate 2022 dose-response analysis found strength gains only when extra protein was paired with training, rising up to about 1.5 g per kg per day and not beyond. In about four out of five of the 74 trials, participants were already eating at least 1.2 g per kg per day before any protein was added, so most of this research compares an intake above the RDA with a higher one.

Trials that started near the RDA and involved no training programme point in different directions. A six-month double-blind trial of 92 men aged 65 and over with limited physical function found that raising intake from 0.8 to 1.3 g per kg per day did not change lean mass, strength, power or walking speed, although fat mass fell by about 1.1 kg more on the higher intake. A six-month trial of 276 adults averaging about 75 years old found that dietary advice lifting intake from about 0.8 to 1.2 g per kg per day shortened a 400 metre walk by about 12 seconds and raised leg strength, with no change in body composition or grip strength. Separately, newer methods for estimating the protein requirement itself place it roughly 30 to 50 percent above the older nitrogen balance method that the RDA rests on, which for people who are not athletes is higher than the RDA and below the 1.6 g per kg level where the training trials stopped showing added lean mass. A 2025 review commissioned through a US federal agency to inform an update of the reference values judged the research published since 2000 insufficient to set an average requirement. A 2020 pooled analysis of 18 randomized trials kept only trials whose comparison group ate the RDA. It found an average lean mass advantage of 0.32 kg for an average intake near 1.3 g per kg. The advantage appeared in 14 comparisons on energy-restricted diets (0.36 kg) and in 3 comparisons with resistance training (0.77 kg), and not in 7 comparisons with neither (0.08 kg, with a range from a loss of 0.59 kg to a gain of 0.75 kg).

The training evidence comes mainly from three pooled analyses. A 2018 analysis of 49 trials with 1,863 participants found that protein supplementation during at least six weeks of resistance training added 0.30 kg of fat-free mass and 2.49 kg to one-repetition maximum strength. Fat-free mass gains did not rise further once total intake passed about 1.62 g per kg per day, and the effect was smaller in older people and larger in people who were already trained. The 2022 analysis of 74 trials found the lean mass effect reached significance at 1.2 to 1.59 g per kg per day in adults 65 and older and at 1.6 g per kg or more in younger adults. Its strength results were slight and rated low certainty, effects on physical function tests were marginal, and effects on handgrip strength were unclear. The 2022 dose-response analysis of 82 reports found strength rose about 0.72 percent for each 0.1 g per kg increase in daily intake up to 1.5 g per kg.

The RDA is a nitrogen balance figure. A 2003 pooled analysis of 235 healthy adults across 19 studies estimated a median requirement of 0.65 g per kg per day and put the intake covering 97.5 percent of healthy adults at 0.83 g per kg, the basis for the current reference value. That measures the intake at which the nitrogen people take in matches the nitrogen they lose, not the intake that produces the most muscle. A 2007 study in eight young men using indicator amino acid oxidation, which tracks when extra protein stops changing how a labelled amino acid is burned, estimated a mean requirement of 0.93 and a population-safe intake of 1.2 g per kg per day. A 2025 analysis comparing 43 nitrogen balance reports with 17 oxidation reports found the oxidation estimates about 36 percent higher in non-athletes (0.88 versus 0.64 g per kg per day) and 27 percent higher in athletes (1.61 versus 1.27). The 2025 government-commissioned review found 66 studies of protein or amino acid requirements published from 2000 to May 2024 across all ages. For adults aged 19 to 50 it counted 16, with protein itself studied only in men, and six for adults over 50. Its full report says that where more than two studies existed, their differing designs and methods made combining them impossible.

For protein without exercise, a companion 2025 review from the same programme examined muscle, bone and kidney outcomes. Of 81 studies, 13 were judged at low or moderate risk of bias, and the reviewers rated the evidence insufficient. Among nine randomized trials with muscle outcomes, three of four found no difference in total lean mass, all four that measured fat-free mass found none, and one of three found faster 400 metre walking. That one was the trial of 276 older adults, in which a second group given the same advice plus guidance on timing gained leg strength but did not walk significantly faster, and in which neither participants nor staff were blinded. The single trial of kidney disease risk in adults found no significant effect.

The NIH Office of Dietary Supplements states the RDA as 0.8 g per kg per day for healthy adults, describes more recent data suggesting athletes need 1.2 to 2.0 g per kg per day, and reports average US intakes in 2007 to 2008 of 100 g a day for men and 69 g for women. It describes intakes of two to three times the RDA as not appearing to raise the risk of kidney stones or impair kidney function in healthy adults over several months. On funding: the senior author of the 2018 and 2022 analyses also ran one of the trials both of them pooled and disclosed dairy council support that also funded some included trials, and a 2020 correction added another author's advisory role with a sports supplement company. The 2022 analysis of 74 trials was funded by an industry-supported nonprofit and three of its authors worked for nutrition or ingredient companies. Five of the seven authors of the 2022 dose-response analysis worked for a dairy company, with government funding. The trial in older men was funded by the NIH, with supplements donated by food and nutrition companies. The two 2025 reviews were funded by US federal agencies, and their authors reported no other conflicts. The 2020 analysis with an RDA comparison reported no funding and no conflicts. The trial of 276 older adults was funded by the European Union; protein-enriched foods came from two food companies and were paid for from the grant.