Article: Use it or lose it
There is a common fallacy that eating more protein will result in retaining more muscle mass as we age. Is that true? What does the evidence say?
Aging is characterized by a gradual decline in muscle mass which can lead to frailty (1)(2). Loss of muscle mass and strength increases our risk of falling, and can predict our future ability to live independently. While strength training can be leveraged to maintain and even gain muscle mass as we age, we tend to see a gradual declines of around 1-2% per year after the age of 50 (2).
Use it or lose it. In study after study, the only predictor of muscle mass gain or retention is regular strength training in older adults who consume adequate dietary protein (8)(9)(10)(11)(12)(13). This means that we all need to be strength training at minimum 2 days per week, which is what CDC recommends (6). In the absence of strength training, we see a predictable decline in muscle mass, irrespective of protein intake. Stimulus trumps intake.
Define adequate protein. RDA stands for the "Recommended Daily Allowance", which is the amount needed by 98% of people. By definition, almost half of us will be getting more protein than we need by meeting the RDA. The RDA for protein in women and men over the age of 19 is 46 and 56 grams, respectively (4). Average protein intake in the US is around double the RDA.
We often hear about protein intake requirements in terms of grams of protein per bodyweight per day, but the real equation is 0.8 grams per kg of ideal lean body mass (4). Ideal lean body mass in women is estimated to be about 100 lbs + 5 lbs for every inch above 5 feet in height. For men, it's 106 lbs + 6 lbs for every inch above 5 feet in height. For example, a 5'2" woman would be estimated to have an ideal lean body mass of 110 lbs. This calculation is often erroneously made using our current body weight, which is only appropriate for body builders with extremely low body fat. Remember that some body fat is required for health and so that 110 lbs of ideal lean body mass does not account for healthy fat mass.
Is there a benefit to eating more protein with strength training? Increasing protein intake above the RDA in middle-aged and older adults (ages 50+) does not appear to improve muscle mass and strength (5)(8)(9)(10)(11)(12)(13). A meta-analysis focusing purely on protein supplementation interventions, without strength training, failed to find any benefit for consuming more than the RDA for protein in older adults in terms of muscle mass retention and slowing muscle loss (5).
Harvard researchers took it one step further, randomizing older men to one of four groups placed on a strength training regimen (8).
Group 1: RDA protein + placebo
Group 2: 1.3g/kg/day protein + placebo
Group 3: RDA protein + testosterone
Group 4: 1.3g/kg/day protein + testosterone
Protein intake made no statistically significant difference in either group (graph below) (8).
What about the studies showing an increase in lean mass with higher protein intakes? Yes, I've seen these too! The results tends to differ when we compare study type: observational versus interventional. In observational studies, increasing protein intake appears to correlate with lean body mass... But that correlation disappears when we look at interventional studies. Actually place participants on a higher protein diet and we find no statistically significant difference in functional skeletal muscle size and function in older adults (5)(8)(9)(10)(11)(12)(13).
Understanding lean body mass measurement. Lean mass includes bones, muscles and organs. In studies where MRI scans are used to evaluate where changes in lean mass are occurring, the gains in lean mass appear to be in increased organ size (7)(9)(10). This may be due to swelling of the internal organs like the liver and kidneys (which is not ideal) (7)(9)(10). Other causes can be increased water retention in the muscles, which can skew lean mass readings (9). In studies focusing on actual amounts of skeletal muscle gain, there does not appear to be a benefit for higher protein recommendations older adults (5)(8)(10)(11)(12)(13).
What do I think? Muscle mass tends to decline with age, but this can be offset by engaging in a regular strength training regimen. Strength in the legs and arms is directly correlated with longevity and independence. Aim for adequate protein intake (the RDA), focus on overall diet quality instead of fixating on macronutrients, and commit to a regular strength training regimen. Simply consuming adequate dietary protein is not enough.
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References
Age-related changes in the structure and function of skeletal muscles. Faulkner et al. Journal of Clinical Experimental Pharmacology and Physiology. (2007) https://doi.org/10.1111/j.1440-1681.2007.04752.x
Frailty in older adults: evidence for a phenotype. Fried et al. The Journals of Gerontology. (2001) https://doi.org/10.1093/gerona/56.3.m146
A Multicomponent Exercise Intervention that Reverses Frailty and Improves Cognition, Emotion, and Social Networking in the Community-Dwelling Frail Elderly: A Randomized Clinical Trial. Terazona-Santabalbina et al. Journal of the American Medical Director Association. (2017) https://doi.org/10.1016/j.jamda.2016.01.019
Dietary Reference Intakes. Institute of Medicine of the National Academies. (2006) https://nap.nationalacademies.org/read/11537/chapter/59#536
The impact of dietary protein or amino acid supplementation on muscle mass and strength in elderly people: Individual participant data and meta-analysis of RCT's. Tieland et al. The Journal of Nutrition Health and Aging. (2017) https://doi.org/10.1007/s12603-017-0896-1
How much physical activity do adults need? Center for Disease Control and Prevention (CDC). (n.d.) https://www.cdc.gov/physicalactivity/basics/adults/index.htm#:~:text=Physical%20activities%20to%20strengthen%20your,addition%20to%20your%20aerobic%20activity.
Muscle or Nothing! Where Is the Excess Protein Going in Men with High Protein Intakes Engaged in Strength Training? Reidy. Journal of Nutrition. (2020) https://doi.org/10.1093/jn/nxz322
Effect of Protein Intake on Lean Body Mass in Functionally Limited Older Men A Randomized Clinical Trial. Bhasin et al. JAMA. (2018) https://jama.jamanetwork.com/article.aspx?doi=10.1001/jamainternmed.2018.0008&utm_campaign=articlePDF%26utm_medium=articlePDFlink%26utm_source=articlePDF%26utm_content=jamainternmed.2018.0008
Role of Ingested Amino Acids and Protein in the Promotion of Resistance Exercise–Induced Muscle Protein Anabolism. Reidy and Blake. The Journal of Nutrition. (2016) https://doi.org/10.3945/jn.114.203208
The effects of dietary protein intake on appendicular lean mass and muscle function in elderly men: a 10-wk randomized controlled trial. Cameron et al. American Journal of Clinical Nutrition. (2017) https://doi.org/10.3945/ajcn.117.160325
The effect of daily protein supplementation, with or without resistance training for 1 year, on muscle size, strength, and function in healthy older adults: A randomized controlled trial. Mertz et al. American Journal of Clinical Nutrition (2021) https://doi.org/10.1093/ajcn/nqaa372
Two-Year Whey Protein Supplementation Did Not Enhance Muscle Mass and Physical Function in Well-Nourished Healthy Older Postmenopausal Women. Zhu et al. The Journal of Nutrition. (2015) https://doi.org/10.3945/jn.115.218297
Protein Supplementation Does Not Significantly Augment the Effects of Resistance Exercise Training in Older Adults: A Systematic Review. Thomas et al. Journal of the American Medical Directors Association. (2016) https://doi.org/10.1016/j.jamda.2016.07.002
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