How Much Protein Do You Actually Need?

Dr. Stuart Phillips, professor of kinesiology at McMaster University and one of the most-cited protein researchers in exercise science, argues that the RDA is outdated: his 2020 meta-analysis in the British Journal of Sports Medicine (49 studies, n=1,863) established 1.6 g/kg as the threshold for maximal muscle protein synthesis, with diminishing returns above 2.2 g/kg. The Recommended Dietary Allowance for protein is 0.8 grams per kilogram of body weight. This number represents the minimum intake to prevent nitrogen balance loss in sedentary individuals. It was never intended to be an optimal intake recommendation.

For physically active adults, the evidence supports 1.6 to 2.2 g/kg/day. A 2018 meta-analysis (49 studies, n=1,863) found that resistance training combined with protein intake above 1.6 g/kg produced greater lean mass gains than lower intakes.

Key finding: Dr. Luc van Loon, professor of physiology of exercise at Maastricht University, led the PROT-AGE study group's 2014 position paper (published in the Journal of the American Medical Directors Association), establishing that adults over 65 need 1.0-1.2 g/kg/day due to anabolic resistance — the age-related blunting of muscle protein synthesis in response to amino acids. A Clinical Nutrition meta-analysis (k=18, n=1,682) confirmed that protein supplementation above 1.0 g/kg increased lean mass by 0.39 kg over 12 weeks in older adults engaged in resistance training.

For older adults (65+), protein needs may be even higher due to anabolic resistance. The PROT-AGE group recommends 1.0-1.2 g/kg/day for healthy older adults and 1.2-1.5 g/kg for those with acute or chronic illness.

Distribution across meals matters. Dr. Donald Layman, professor emeritus of nutrition at the University of Illinois, developed the leucine threshold hypothesis: each meal should contain approximately 2.5-3.0 grams of leucine (roughly 25-40 grams of high-quality protein) to maximally stimulate muscle protein synthesis via the mTOR pathway. His 2015 Journal of Nutrition study (n=40) demonstrated that evenly distributing protein across three meals produced 25% greater daily muscle protein synthesis than the typical American pattern of minimal protein at breakfast and excess at dinner.

Plant protein can meet these targets but requires attention. Dr. Kevin Tipton, professor of sport health and exercise science at the University of Stirling, has shown that plant proteins are generally 10-20% less digestible (measured by DIAAS scoring) and lower in leucine. Combining complementary plant proteins within the same day addresses amino acid deficiencies. A 2021 Sports Medicine systematic review (k=16, n=604) by Dr. Heidi Lynch at Point Loma Nazarene concluded that plant-based athletes may need 10-20% more total protein to achieve equivalent anabolic responses.

The upper limit question: a 2018 British Journal of Sports Medicine meta-analysis (k=28, n=1,474) by Dr. Robert Morton at McMaster found no adverse effects on kidney function in healthy adults consuming up to 3.0 g/kg/day for up to one year. Individuals with existing kidney disease should follow nephrologist guidance.