As we age, our bodies undergo numerous physiological changes that can affect our health and well-being. One of the critical areas impacted by aging is muscle mass and function. Protein intake becomes increasingly important as we grow older due to a phenomenon known as anabolic resistance, which is the decreased response of muscle protein synthesis to dietary protein.
What is Anabolic Resistance?
Anabolic resistance[1] refers to the reduced efficiency of muscle protein synthesis (MPS) in response to dietary protein intake and physical activity in older adults. It means that aging muscles require more protein to achieve the same anabolic effect (muscle building) as younger muscles.
In younger individuals, the consumption of protein stimulates muscle protein synthesis effectively, leading to muscle maintenance and growth. However, as we age, several factors contribute to a diminished response to protein intake:
- Decreased Muscle Sensitivity:[2] Aging muscles become less sensitive to the anabolic stimuli provided by protein intake. This means that the same amount of dietary protein that once effectively stimulated MPS in younger individuals is less effective in older adults.
- Hormonal Changes:[3] Hormones such as growth hormone, insulin-like growth factor 1 (IGF-1), and testosterone play significant roles in muscle protein synthesis. As we age, the levels and activity of these hormones decline, contributing to reduced muscle anabolism.
- Reduced Physical Activity:[4] Physical activity, particularly resistance exercise, is a powerful stimulus for muscle protein synthesis. Older adults may experience reduced levels of physical activity due to various factors, including decreased mobility and health conditions, which further exacerbate anabolic resistance.
Research has shown that older adults need higher amounts of dietary protein to stimulate muscle protein synthesis effectively. Moore et al.[5] investigated the amount of dietary protein needed to maximize muscle protein synthesis (MPS) in healthy older versus younger men. They found that older men need approximately 0.40 grams of protein per kilogram of body weight per meal to achieve maximum MPS, while younger men require about 0.24 grams per kilogram. This "anabolic resistance" in older adults suggests that their muscles do not respond as efficiently to lower amounts of protein, necessitating higher intake to maintain or increase muscle mass.
What is the RDA for Protein?
While the Recommended Dietary Allowance (RDA) for adults over 19 is set at 0.8 grams per kilogram of body weight per day, evidence suggests that this may not be sufficient for older adults due to the age-related decline in muscle mass and function, known as sarcopenia.
A review paper by Traylor et al.[6] highlights the inadequacy of the current RDA for protein in older individuals. Research indicates that older adults have a lower anabolic response to dietary protein, meaning their muscles do not build and repair as efficiently as in younger individuals.
Keep in mind that the RDA is set to avoid a deficiency, rather than to suggest what is optimal for a particular age group.
How Much Protein Do Older Adults Need to Consume?
Research suggests[7] that consuming between 1.2 to 1.6 g/kg/day of high-quality protein is more effective in maintaining muscle mass and function in older individuals. This increase is necessary due to anabolic resistance, where aging muscles have a diminished response to protein, necessitating higher intake levels to stimulate muscle protein synthesis adequately.
Higher protein consumption in older adults helps prevent sarcopenia—the loss of muscle mass and strength that leads to frailty and loss of independence. Observational studies, as cited in their review by Phillips et al.,[7] have shown that increased protein intake is associated with better muscle mass retention and improved physical function. Additionally, higher protein diets enhance satiety and support weight management, which is crucial for older adults who often experience reduced appetite.
Despite concerns, there is no evidence linking higher protein intakes to renal disease or adverse bone health. On the contrary, when paired with adequate calcium and vitamin D, higher protein intakes can support bone health. Therefore, revising the RDA for older adults to at least 1.2 to 1.6 g/kg/day of high-quality protein can significantly contribute to healthier aging, preserving muscle mass, and improving overall quality of life.[7]
Sources of Protein for Aging Adults
To achieve the higher protein needs, older adults should focus on incorporating high-quality protein sources into their diet. These include:
- Lean Meats: Chicken, turkey, and lean cuts of beef and pork provide high-quality protein with essential amino acids.
- Fish and Seafood: Salmon, tuna, and other fish are excellent sources of protein and also provide beneficial omega-3 fatty acids.
- Dairy Products: Milk, yogurt, and cheese are rich in protein and calcium, which support bone health.
- Plant-Based Proteins: Beans, lentils, tofu, and quinoa are great options for those following a plant-based diet.
- Eggs: Eggs are a versatile and nutrient-dense source of protein.
- Nuts and Seeds: Almonds, walnuts, chia seeds, and flaxseeds offer protein along with healthy fats and fiber.
- Protein Powders: Whey protein, casein, and plant-based protein powders provide a convenient way to increase protein intake, especially for those with higher protein needs or limited appetite. We recommend 100% whey protein isolate because it is a high quality, bioavailable protein source that is easy on the stomach and tastes great!
Conclusion
Increased Protein Needs: Older adults require higher protein intakes (1.2 to 1.6 g/kg/day) compared to the current RDA of 0.8 g/kg/day to combat anabolic resistance and maintain muscle mass and function.
Combatting Sarcopenia: Higher protein consumption helps prevent age-related muscle loss and strength decline, reducing the risk of frailty and loss of independence.
Improved Physical Function: Studies show increased protein intake is linked to better muscle mass retention and enhanced physical function in older adults.
Weight Management: Higher protein diets improve satiety and support weight management, crucial for older adults with reduced appetite.
No Adverse Health Effects: There is no evidence linking higher protein intakes to renal disease or adverse bone health; instead, it supports bone health when combined with adequate calcium and vitamin D.
Sources of Protein: Lean meats, fish, dairy, plant-based proteins, eggs, nuts, seeds, and protein powders are excellent sources to meet the higher protein needs of older adults.
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References:
1. Burd, Nicholas A.; Gorissen, Stefan H.; van Loon, Luc J.C.. Anabolic Resistance of Muscle Protein Synthesis with Aging. Exercise and Sport Sciences Reviews 41(3):p 169-173, July 2013. | DOI: 10.1097/JES.0b013e318292f3d5
2. Straight, C. R.; Ades, P. A.; Toth, M. J.; Miller, M. S. Age-Related Reduction in Single Muscle Fiber Calcium Sensitivity Is Associated with Decreased Muscle Power in Men and Women. Experimental Gerontology, 2018, 102, 84–92. https://doi.org/10.1016/j.exger.2017.12.007.
3. Pataky, M. W.; Young, W. F.; Nair, K. S. Hormonal and Metabolic Changes of Aging and the Influence of Lifestyle Modifications. Mayo Clinic Proceedings, 2021, 96 (3), 788–814. https://doi.org/10.1016/j.mayocp.2020.07.033.
4. Milanović, Zoran et al. “Age-related decrease in physical activity and functional fitness among elderly men and women.” Clinical interventions in aging vol. 8 (2013): 549-56. doi:10.2147/CIA.S44112
5. Moore, D. R.; Churchward-Venne, T. A.; Witard, O.; Breen, L.; Burd, N. A.; Tipton, K. D.; Phillips, S. M. 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. https://doi.org/10.1093/gerona/glu103.
6. Traylor, D. A.; Gorissen, S. H. M.; Phillips, S. M. Perspective: Protein Requirements and Optimal Intakes in Aging: Are We Ready to Recommend More Than the Recommended Daily Allowance? Adv Nutr, 2018, 9 (3), 171–182. https://doi.org/10.1093/advances/nmy003.
7. Phillips, S. M.; Chevalier, S.; Leidy, H. J. Protein “Requirements” beyond the RDA: Implications for Optimizing Health. Appl. Physiol. Nutr. Metab., 2016, 41 (5), 565–572. https://doi.org/10.1139/apnm-2015-0550.
