Protein and Longevity: How Much You Actually Need and Why It Changes With Age
The RDA for protein, 0.8 g/kg of body weight a day, is set at the intake that meets the needs of nearly all healthy adults; a meta-analysis of nitrogen-balance studies put that level at 0.83 g/kg.8 Older adults and people who train may benefit from more, but how much protein is best for long-term health is less settled than popular advice suggests.2,4
- No protein target for longevity has been established. For people doing resistance training, a meta-analysis found extra protein stopped adding muscle gains above about 1.6 g/kg a day.3 For older adults, the PROT-AGE expert group recommends at least 1.0 to 1.2 g/kg a day, at least 1.2 for those who exercise, and 1.2 to 1.5 for most people with acute or chronic illness.4
- Older muscle needs more protein per meal to respond fully: muscle protein synthesis plateaued at about 0.4 g/kg per meal in older men versus 0.24 g/kg in younger men, roughly 30 g for a 75-kg older man.5
- In people with healthy kidneys, a meta-analysis of 28 trials found that higher protein intakes did not adversely affect kidney function.6 People with chronic kidney disease should follow their clinician's advice on protein.
- Protein distribution may matter less than once thought: in a study of 8 adults, spreading protein evenly across three meals produced 25 percent more 24-hour muscle protein synthesis than eating most of it at dinner,7 but in an 8-week trial in 14 older adults, even and dinner-heavy patterns made no difference to lean mass, strength or function.9
- Age may change the picture: in US survey data, adults aged 50 to 65 who ate the most protein had 75% higher overall mortality over 18 years, an association weakened when the protein was plant-based, while over 65 high protein went with lower overall mortality.2 These are observational findings.
The Protein Adequacy Problem
The RDA for protein, 0.8 g/kg a day, is often read as a target. It is set at the 97.5th percentile of individual requirements, the intake that covers nearly all healthy adults; in a meta-analysis of nitrogen-balance studies, the median requirement was 0.65 g/kg and the RDA level 0.83 g/kg.8
Needs rise with training. A review for athletes suggested 1.3 to 1.8 g/kg a day spread over 3 to 4 meals to maximize muscle protein synthesis, and up to 1.8 to 2.0 g/kg during calorie restriction to protect lean mass.1 In a meta-analysis of resistance-training trials, gains in lean mass from extra protein levelled off above about 1.6 g/kg a day.3
Protein and the Aging Paradox
The relationship between protein and longevity is not simply "more is better". In a US analysis, high protein intake at ages 50 to 65 was linked to a 75% increase in overall mortality and a four-fold increase in cancer death over 18 years, associations that were abolished or weakened when the protein came from plants; over 65, high protein went with lower cancer and overall mortality, though with a five-fold increase in diabetes mortality across all ages.2
The authors linked these findings to growth hormone and IGF-1 signaling, which protein restriction reduces; mouse experiments supported the link but also showed harm from low-protein diets in very old animals.2 Because the human data are observational, they cannot show that protein itself caused the differences.
Plant or Animal Protein?
The source may matter more than the amount. In two large US cohorts of 131,342 health professionals, higher animal protein intake was linked to higher cardiovascular mortality, and each additional 3% of energy from plant protein to about 10% lower all-cause mortality; these associations appeared only in people with at least one unhealthy lifestyle factor, such as smoking, heavy drinking, excess weight or inactivity. Replacing protein from processed red meat with plant protein was linked to the largest difference.10 Like the US survey data above, these are observational findings, so they cannot separate protein from the rest of the diet.
References
- 1Phillips SM, Van Loon LJ. "Dietary protein for athletes: from requirements to optimum adaptation." J Sports Sci. 2011;29 Suppl 1:S29-38. PubMed · DOI
- 2Levine ME, et al. "Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population." Cell Metab. 2014;19(3):407-17. PubMed · DOI
- 3Morton RW, et al. "A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults." Br J Sports Med. 2018;52(6):376-384. PubMed · DOI
- 4Bauer J, et al. "Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group." J Am Med Dir Assoc. 2013;14(8):542-59. PubMed · DOI
- 5Moore DR, et al. "Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men." J Gerontol A Biol Sci Med Sci. 2015;70(1):57-62. PubMed · DOI
- 6Devries MC, et al. "Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets: A Systematic Review and Meta-Analysis." J Nutr. 2018;148(11):1760-1775. PubMed · DOI
- 7Mamerow MM, et al. "Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults." J Nutr. 2014;144(6):876-80. PubMed · DOI
- 8Rand WM, et al. "Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults." Am J Clin Nutr. 2003;77(1):109-27. PubMed · DOI
- 9Kim IY, et al. "Protein intake distribution pattern does not affect anabolic response, lean body mass, muscle strength or function over 8 weeks in older adults: A randomized-controlled trial." Clin Nutr. 2018;37(2):488-493. PubMed · DOI
- 10Song M, et al. "Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality." JAMA Intern Med. 2016;176(10):1453-1463. PubMed · DOI
