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Optimal Protein intake for older adults

Highlights: Muscle mass loss occurs at a rate of 2% per year after the age of 30. Current recommended minimum protein intakes may not be enough to stave off sarcopenia. Quality of protein is important.

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Note: for ease of reading in this article muscle mass refers to skeletal muscle mass

 

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There are heated debates about the optimum protein intake for adults, not only in scientific research but also in the public sphere. The intake level needed to avoid risk of deficiency and disease is called the Recommended Dietary Intake (RDI)* (1) (2) – it is the amount of nutrient intake required to keeps you out of hospital. For adults the protein RDI is generally accepted as > 0.8 g/kg body weight with adjustments for age and gender see Table 1 (1). It opens the question about where the optimum intake level for protein is. Multiple studies have proposed that this level is too low for many population groups and adults may benefit from higher intakes as well as better quality protein (3).

Beef Steak
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Sarcopenia is defined as a progressive, age-related loss of muscle mass and function – estimated at 3-8% per decade after the age of 30 years (4). It is estimated that over 30% of adults over 60 years have significant sarcopenia. Prevalence increase to over 50% for those over 80 years. This matter because muscle function determines independence as you get older (5). Being able to do daily activities, like getting out of a chair without help, picking up groceries, reaching for items in high cupboards, climbing stairs and catching yourself when you trip to prevent a fall, makes life easy.

 

Anabolic resistance increases as we get older. This means that building and maintaining muscle is more difficult to achieve despite the same muscle building stimulus from resistance training and protein ingestion. Muscle fibres are constantly being broken down from daily activities. Our bodies are continually making new fibres and repairing damaged muscle in order to maintain functional movement.

 

How do we make protein for muscle fibres? Resistance training is well accepted as the first line of defence against age related muscle loss (3) but adherence can be low in some population groups.  We also need to ingest sufficient protein to stimulate muscle synthesis. Specifically, we need the amino acid leucine. Amino acids are the building blocks for proteins, like different colour Lego blocks. They have functions on their own, for instance as neurotransmitters like glutamate or are put together for specific roles and functions like making insulin, collagen or muscle cells. The amino acid leucine is the key signal stimulus for muscle protein synthesis (6). To overcome the inevitable anabolic resistance of aging, the leucine content and bioavailability becomes increasingly important to prioritise in the diet.

 

​​​​How much leucine and where do you get it?

Various studies have shown that >2.5g/meal is required for the restorative impact of leucine (2, 3, 6-8). This is roughly 7.5g of leucine per day – more than double the RDI (9). Our essential need for leucine drives aspects of our requirement for dietary protein. Animal protein foods have a higher percentage of leucine content compared to plant sources (12% in whey protein and 6% in grains) (10). The average leucine content for food sources is around 8% equating to roughly 30g of high-quality protein per meal to stimulate protein synthesis.

 

Protein quality depends on the combination of essential amino acids and the digestibility. The DIAAS (digestible indispensable amino acid score) is used the rank protein quality in terms of essential amino acid content in protein in mg/g of protein (11). A score of 75-100% is considered good but not an optimal 100% supply of essential amino acids. An optimal source of all essential amino acids in required ratios will give a score of >100%. Many factors like, fiber content, can lower the digestibility of protein in foods. The highest DIAAS scores are found in isolated protein supplements like whey and soy  (12). Table 2 lists a few well-known protein supplement powders and whole food sources (13). If one or more essential amino acid is absent from the food source the DIAAS score is reduced as is the case for collagen powders where the limiting (absent) amino acid is tryptophan. Hence collagen cannot be considered a replacement for protein.

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The acceptable range of protein intake is 10-35% of total energy intake, or 0.8-2.5 g/kg (14). To put this in perspective, for an adult weighing 70kg the protein intake range is 56-175 g. It is important to point out here that this is grams of protein content, not the weight of the protein containing food. Table 3 shows protein and leucine content for common food in everyday serving sizes.

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Final thoughts

Observational studies show that a higher protein intake is associated with increase in lean mass and better physical function and the effect is more pronounced in females (5). This translates to a reduced risk of developing osteoporosis and fracture from falling (17). Physical function was improved with supplementation even in older adults with compromising conditions (18). Other research has shown that muscle mass decline with diets that contain the RDI protein content (19, 20).

 

Protein, together with adequate calcium and vitamin D, is protective for bone health and there is no evidence that ‘too much’ protein will lead to bone loss or decrease in renal function (21-28).

 

Research indicates RDA is insufficient for older adults to offset effect of age related anabolic resistance(2).

 

October 2020

 

* Confusingly US/Canadian terminology use Recommended Dietary Allowance (RDA).

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Reference:

  1. Nutrient Reference Values. Protein. In: NHMRC, editor. Australia2014.

  2. Phillips SM, Paddon-Jones D, Layman DK. Optimizing Adult Protein Intake During Catabolic Health Conditions. Advances in Nutrition. 2020;11(4):S1058-S69.

  3. Phillips SM, Chevalier S, Leidy HJ. Protein “requirements” beyond the RDA: implications for optimizing health. Applied Physiology, Nutrition, and Metabolism. 2016;41(5):565-72.

  4. Anton SD, Woods AJ, Ashizawa T, Barb D, Buford TW, Carter CS, et al. Successful aging: Advancing the science of physical independence in older adults. Ageing Res Rev. 2015;24(Pt B):304-27.

  5. Gregorio L, Brindisi J, Kleppinger A, Sullivan R, Mangano KM, Bihuniak JD, et al. Adequate dietary protein is associated with better physical performance among post-menopausal women 60-90 years. J Nutr Health Aging. 2014;18(2):155-60.

  6. Devries MC, McGlory C, Bolster DR, Kamil A, Rahn M, Harkness L, et al.  Leucine, Not Total Protein, Content of a Supplement Is the Primary  Determinant of Muscle Protein Anabolic Responses in Healthy Older Women.  The Journal of nutrition. 2018;148(7):1088-95.

  7. Katsanos CS, Kobayashi H, Sheffield-Moore M, Aarsland A, Wolfe RR. A high  proportion of leucine is required for optimal stimulation of the rate of muscle  protein synthesis by essential amino acids in the elderly. Am J Physiol    Endocrinol Metab. 2006;291(2):E381-7

  8. Murphy CH, Saddler NI, Devries MC, McGlory C, Baker SK, Phillips SM.   Leucine supplementation enhances integrative myofibrillar protein synthesis in  free-living older men consuming lower- and higher-protein diets: a parallel-group crossover study. The American Journal of Clinical Nutrition.  2016;104(6):1594-606.

  9. Bauer J, Biolo G, Cederholm T, Cesari M, Cruz-Jentoft AJ, Morley JE, 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.

  10. Gorissen SHM, Crombag JJR, Senden JMG, Waterval WAH, Bierau J, Verdijk  LB, et al. Protein content and amino acid composition of commercially  available plant-based protein isolates. Amino Acids. 2018;50(12):1685-95.

  11. Nations FaAOotU. Dietary protein quality evaluation in human nutrition.  Report of an FAO expert consultation. FOA Food and Nutrition Paper 92. 2013.

  12. Agropur US. PDCAAS to DIAAS: A new way to look at protein quality. USA  [Available from: https://www.agropuringredients.com/pdcaas-to-diaas-a-new-way-to-look-at-protein-quality/.

  13. Phillips S. Current Concepts and Unresolved Questions in Dietary Protein Requirements and Supplements in Adults. Frontiers in Nutrition. 2017;4.

  14. Wolfe RR, Cifelli AM, Kostas G, Kim I-Y. Optimizing Protein Intake in Adults: Interpretation and Application of the Recommended Dietary Allowance  Compared with the Acceptable Macronutrient Distribution Range. Advances in nutrition (Bethesda, Md). 2017;8(2):266-75.

  15. FSANZ. Australian Food Composition Database. In: Health, editor. Canberra2019.

  16. Sports Dietitians Australia. fact sheet: Protein and amino acid  supplementation Australia: SDA; 2011 [Available from:   https://www.sportsdietitians.com.au/wp-content/uploads/2015/04/110701-Protein-Supplementation_General.pdf.

  17. Isanejad M, Mursu J, Sirola J, Kröger H, Rikkonen T, Tuppurainen M, et al. Association of protein intake with the change of lean mass among elderly  women: The Osteoporosis Risk Factor and Prevention - Fracture Prevention Study (OSTPRE-FPS). J Nutr Sci. 2015;4:e41.

  18. Avenell A, Smith TO, Curtain JP, Mak JC, Myint PK. Nutritional supplementation for hip fracture aftercare in older people. The Cochrane  database of systematic reviews. 2016;11(11):Cd001880.

  19. Campbell WW, Trappe TA, Jozsi AC, Kruskall LJ, Wolfe RR, Evans WJ. Dietary  protein adequacy and lower body versus whole body resistive training in older humans. J Physiol. 2002;542(Pt 2):631-42.

  20. Mitchell CJ, Milan AM, Mitchell SM, Zeng N, Ramzan F, Sharma P, et al. The effects of dietary protein intake on appendicular lean mass and muscle function in elderly men: a 10-wk randomized controlled trial. Am J Clin Nutr.      2017;106(6):1375-83.

  21. Shams-White MM, Chung M, Du M, Fu Z, Insogna KL, Karlsen MC, et al.  Dietary protein and bone health: a systematic review and meta-analysis from  the National Osteoporosis Foundation. Am J Clin Nutr. 2017;105(6):1528-43.

  22. Shams-White MM, Chung M, Fu Z, Insogna KL, Karlsen MC, LeBoff MS, et al.  Animal versus plant protein and adult bone health: A systematic review and  meta-analysis from the National Osteoporosis Foundation. PloS one.2018;13(2):e0192459.

  23. Devries MC, Sithamparapillai A, Brimble KS, Banfield L, Morton RW, Phillips  SM. 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. The Journal of nutrition.  2018;148(11):1760-75.

  24. Van Elswyk ME, Weatherford CA, McNeill SH. A Systematic Review of Renal Health in Healthy Individuals Associated with Protein Intake above the US  Recommended Daily Allowance in Randomized Controlled Trials and  Observational Studies. Adv Nutr. 2018;9(4):404-18.

  25. Schwingshackl L, Hoffmann G. Comparison of high vs. normal/low protein  diets on renal function in subjects without chronic kidney disease: a  systematic review and meta-analysis. PloS one. 2014;9(5):e97656.

  26. Surdykowski AK, Kenny AM, Insogna KL, Kerstetter JE. Optimizing bone  health in older adults: the importance of dietary protein. Aging health.  2010;6(3):345-57.

  27. Groenendijk I, den Boeft L, van Loon LJC, de Groot L. High Versus low  Dietary Protein Intake and Bone Health in Older Adults: a Systematic Review  and Meta-Analysis. Comput Struct Biotechnol J. 2019;17:1101-12.

  28. Bilancio G, Cavallo P, Ciacci C, Cirillo M. Dietary Protein, Kidney Function and  Mortality: Review of the Evidence from Epidemiological Studies. Nutrients. 2019;11(1).

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