by Whitney Crouch, RDN, CLT
The US population is living longer than ever before, with older adults increasingly making up a larger portion of that population. The US Census Bureau projects that the US population aged ≥65 years is expected to double by the year 2050.1 Aging is associated with changes in body composition, and there is evidence that these changes vary by ethnicity and gender.2
The loss of lean muscle mass that occurs with advancing age is termed sarcopenia (primary), which can be explained as an imbalance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Sarcopenia can also be hastened by nutritional deficiencies, hormonal changes, metabolic disturbances, comorbidities, inflammation, drug adverse effects, lack of physical activity, genetic predisposition, and the effects of early environment (secondary).3 This condition often leads to a concomitant loss of strength, increased frailty and risk of falls, and an overall loss of functional independence in the elderly.
In addition to changes in strength and functionality, reduced muscle mass increases the development of metabolic conditions including impaired glucose tolerance (IGT), obesity, and type 2 diabetes.3 Due to the impact on health and quality of life, sarcopenia was recently included in the ICD-10 classification of diseases.4
Age, sex, and ethnic differences in muscle mass
Researchers looking at African Americans (AA), Hispanics, non-Hispanic whites, and Asians examined the skeletal muscle mass of over 1,700 individuals.2 Not surprisingly, they found men to have a higher skeletal muscle-to-fat ratio than women, however there were differences based on age and ethnicity.2
Gender & Age: While the higher absolute amount of muscle mass was higher in men, the trend over time differed between men and women; men achieved their highest muscle mass in the 20-30 year old range, while women maintain their muscle mass a bit longer – typically through about 40 years old, declining around menopause.2Ethnicity: On average, AA males and females demonstrated the highest levels of skeletal muscle mass across the lifespan, followed by non-Hispanic whites, Hispanics, and then Asians.2
Physical fitness and sarcopenia
Since sarcopenia is typified by the loss of lean body mass with aging, the question should be asked – how can one mitigate this process to maintain muscle mass throughout the lifespan?
A 2017 meta-analysis explored the effects of various levels of physical activity on muscle mass in the aging population.5 The authors noted that many studies have shown that physical inactivity contributes to the development of sarcopenia, while physical activity increases muscle mass and strength in the aging.5
While physical activity reduces muscle loss associated with sarcopenia, not all physical activity is equally effective. “Physical activity” refers to any level of activity beyond seated rest that results from skeletal muscle activation and leads to movement and an increase in energy expenditure.6 “Exercise” refers to planned, structured, repetitive activity aimed to improve fitness.6Endurance-type activities that include aerobic exercises (running, high-intensity interval trainings (HIIT), cycling, etc.) are important for cardiovascular health and improving skeletal muscle oxidative capacity.7 These aerobic activities represent high repetition, low load-bearing exercises. In contrast, resistance training exercises include lower repetition, higher-load bearing exercises that increase power and strength of the muscles being challenged. This type of exercise increases mass of the muscles being trained, while simultaneously increasing glucose uptake into the working muscle groups.7
While optimal muscle mass can be maintained with regular resistance training exercises (3-5 times/week), it is important that individuals who are not well conditioned work their way up to this ability with a proper fitness routine and appropriate nutrition.7
Diet and the aging adult
A healthy lifestyle with regular exercise often goes hand in hand with better overall nutrition intake, both quality and quantity. However, as people age, oftentimes diet quality and quantity can become less than ideal due to socioeconomic factors, psychosocial factors, reduced mobility, reduced independence, dentition challenges, and reduced appetite.4
A ‘healthy diet’ including high consumption of fruits, vegetables, oily fish, and whole grains has been associated with improved grip strength in older adults, and a Mediterranean diet, in particular, has been associated with faster gait speed and reduced risk of frailty syndrome.8-10
Protein intake, supplementation, and muscle protein synthesis
Adequate overall calorie intake, including adequate protein intake (at least 1-1.2 g/kg body weight),11 is an important factor in reducing muscle breakdown in the body. During the aging process, it’s important to recognize that diet quality and quantity are not the only players in the game, and timing of nutrients can matter.
A normal part of the aging process is a decline in MPS related to muscle anabolic resistance. To examine the role of exercise, nutrition, and supplementation on MPS, a systematic review was conducted to examine: 1) exercise alone, 2) amino-acid based nutrition supplementation alone, and 3) exercise plus branched-chain amino acid (BCAA) supplementation.12 The exercise + BCAA arm provided sufficient evidence of age-related anabolic resistance, highlighting that optimization of exercise plus amino acid balance is required to induce a degree of MPS (muscle building).12
Many studies have shown improved muscle protein synthesis when protein is consumed post-workout, especially after a resistance training session.13 Studies also show that protein consumed with meals is best utilized when spread out relatively evenly across the meals for the day, with the exception of post-workout protein intake.11
BCAAs are often discussed in the context of post-workout muscle synthesis, stemming from a theory that they activate intracellular anabolic signaling factors that cause an increase in MPS, with specific focus on leucine.14 This is because leucine has been shown to be the most potent amino acid to stimulate MPS from activation of the nutrient and growth factor-sensing mammalian target of rapamycin complex 1 (mTORC1) and in turn, its downstream targets.15
An important fact to note is that there are a total of 22 amino acids that make up muscle protein.16 There are only 3 BCAAs – leucine, isoleucine, and valine, among the 9 essential amino acids (EAA) and another 11 non-essential amino acids, plus 2 conditionally essential amino acids.17 In a study conducted in healthy elderly adults, researchers found balanced essential amino acids to be primarily responsible for the amino acid-induced stimulation of MPS in the elderly, not the BCAAs alone.18
Bottom line: BCAAs are likely helpful as intracellular stimulators of anabolic signaling to cause muscle protein synthesis (potentially due to the extra leucine they provide), but they should be consumed as a part of an adequate protein diet providing all EAAs.
Other nutritional considerations
In addition to adequate and complete protein intake, more recent research has looked at specific nutrients that also help combat sarcopenia.
HMB
Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the BCAA leucine. In addition to the discussion of leucine’s role in promoting MPS, studies are also honing in on the HMB metabolite. A recent systematic review meta-analyzed 7 randomized, controlled trials that found HMB to be beneficial in preventing muscle atrophy in the aging or bedridden populations.19 Studies investigating interventions that included resistance training exercises also found significant gains in muscle growth and strength while supplementing with HMB.19
The optimal dosage of HMB for muscle improvement is not conclusive: the majority of studies demonstrating benefit to date have utilized 3 g/day of HMB; the HMB dose provided to the treatment groups in the aforementioned meta-analysis ranged between 2-3 g/d.19
Vitamin D
A vast array of studies have looked at the role of vitamin D status and supplementation on musculoskeletal health outcomes in the aging population.
Vitamin D status: The results of many different analyses conclude that individuals with insufficient or deficient levels of 25-hydroxyvitamin D (≤20 ng/mL and ≤10 ng/mL, respectively) are more prone to low bone density conditions, mobility and disability issues, slower gait speed, and weaker handgrip strength.11
Vitamin D supplementation: Research suggests that supplementing with 800-1,000 IU/day of vitamin D3 (but not necessarily higher doses) to achieve 25-hydroxyvitamin D status to ≥20 ng/mL supports normal muscle contractility, improved gait speed, and other measures of frailty.11
Omega-3 fatty acids
The majority of expert groups endorse intakes of 250–500 mg/day of marine-based omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for cardiovascular health, which translates into about 2 servings (140 g, 5 oz) of fatty/oily fish per week,20 but cardiovascular health is not the only consideration when determining the most effective dose of EPA and DHA.
The anabolic role of omega-3 fatty acids on skeletal muscle is thought to be owed to a variety of biochemical and physiological mechanisms: a reduction in pro-inflammatory cytokines and myosteatosis (accumulation of fat within the muscle), an improvement in insulin sensitivity,21 stimulation of MPS via the mTOR-p70S6k signaling pathway,22 and a reduction of mitochondrial reactive oxygen species emission.23
A review of the literature reveals positive changes in individuals with sarcopenia receiving omega-3 supplementation (with 3-6 months of treatment using ≥3 g/day EPA and DHA), netting improvements in functional measures and muscle mass and volume.22-23
Takeaways
Older adults are a large and growing demographic segment of the US population, and therefore, sarcopenia is and will continue to be a major, relevant healthcare issue
Anti-sarcopenic approaches should include regular resistance training exercise (3-5 times/week) and adequate protein intake (1-1.2 g/kg body weight) are recommended
Supplemental BCAAs and HMB may improve muscle protein synthesis and prevent muscle atrophy, which can improve strength training outcomes and prevent muscle loss during periods of inactivity
Vitamin D levels within normal range are shown to support optimal muscle function, and personalized supplementation should be considered to achieve or maintain these levels (at least ≥20 ng/mL)
High-dose of EPA and DHA (≥3 g/day, combined) or high intake of fatty fish may further support anabolism of skeletal muscle tissue
Citations
1. Ortman J et al. United States Census Bureau. An aging nation: the older population in the United States. Population Estimates and Projections. https://www.census.gov/prod/2014pubs/p25-1140.pdf. Accessed October 9, 2018.
2. Silva AM et al. Ethnicity-related skeletal muscle differences across the lifespan. Am J Hum Biol. 2010;22(1):76-82.Cartee GD et al. Exercise promotes healthy aging of skeletal muscle. Cell Metab. 2016;23(6):1034-1047.Fuggle N et al. Sarcopenia. Best Pract Res Clin Rheumatol. 2017;31(2):218–242.Steffl M et aI. Relationship between sarcopenia and physical activity in older people: a systematic review and meta-analysis. Clin Interv Aging. 2017;12:835-845.Caspersen CJ et al. Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research. Public Health Rep. 1985;100:126–131.Egan B et al. Exercise metabolism and the molecular regulation of skeletal muscle adaptation. Cell Metab. 2013;17(2):162-84.Robinson SM et al. Diet and its relationship with grip strength in community-dwelling older men and women: the Hertfordshire cohort study.J Am Geriatr Soc. 2008;56(1):84–90.Shahar DR et al. Adherence to Mediterranean diet and decline in walking speed over 8 years in community-dwelling older adults. J Am Geriatr Soc. 2012;60(10):1881–1888.Bollwein J et al. Dietary quality is related to frailty in community-dwelling older adults. J Gerontol A Biol Sci Med Sci. 2013;68(4):483–489.Tessier AJ et al. An Update on protein, leucine, omega-3 fatty acids, and vitamin D in the prevention and treatment of sarcopenia and functional decline. Nutrients. 2018;10(8):1099.Shad BJ et al. Does the muscle protein synthetic response to exercise and amino acid-based nutrition diminish with advancing age? A systematic review. Am J Physiol Endocrinol Metab. 2016;311(5):E803-E817.Cholewa JM et al. Dietary proteins and amino acids in the control of the muscle mass during immobilization and aging: role of the MPS response. Amino Acids. 2017;49(5):811-820.Blomstrand E et al. Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise. J Nutr. 2006;136(1 Suppl):269S-273S.Anthony JC et al. Leucine stimulates translation initiation in skeletal muscle of postabsorptive rats via a rapamycin-sensitive pathway. J Nutr. 2000;130:2413–2419.Wolff RR. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? J Int Soc Sports Nutr. 2017;14:30.NIH. US National Library of Medicine. MedLine Plus. Amino Acids. https://medlineplus.gov/ency/article/002222.htm. Accessed October 15, 2018.Volpi E et al. Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults. Am J Clin Nutr. 2003;78(2):250-258.Wu H et al. Effect of beta-hydroxy-beta-methylbutyrate supplementation on muscle loss in older adults: a systematic review and meta-analysis. Arch Gerontol Geriatr. 2015;61(2):168-175.Vannice G et al. Position of the Academy of Nutrition and Dietetics: dietary fatty acids for healthy adults. J Acad Nutr Diet. 2014;114(1):136-153.Ewaschuk JB et al. Role of n-3 fatty acids in muscle loss and myosteatosis. Appl Physiol Nutr Metab. 2014;39:654–662.Gray SR et al. Fish oil-derived n-3 polyunsaturated fatty acids for the prevention and treatment of sarcopenia. Curr Opin Clin Nutr Metab Care. 2018;21:104–109.Lalia AZ et al. Influence of omega-3 fatty acids on skeletal muscle protein metabolism and mitochondrial bioenergetics in older adults. Aging. 2017;9:1096–1129.Whitney Crouch, RDN, CLTWhitney Crouch is a Registered Dietitian with a BS in Clinical Nutrition from the University of California, Davis. She has over 10 years of experience across multiple areas of dietetics, specializing in integrative and functional nutrition and low toxicity living. When she’s not writing about nutrition or educating others on non-toxic skincare and hygiene, she’s spending time with her husband and young son. She’s often found running around the bay near her home with the family’s dog or in the kitchen cooking up new ideas to help her picky eater expand his palate.
