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BCAA (Leucine) Supplementation Increases Muscle Protein Synthesis in Healthy Women

by Bianca Garilli, ND

A reduction in muscle mass, strength, and function reduce the independence and health of aging adults. Sarcopenia, the loss of muscle tissue typically associated with the natural aging process, also increases the risk for morbidity and mortality through its association with chronic illnesses including cardiovascular disease, diabetes, and obesity. The greater the degree of sarcopenia, the higher the risk of these disease processes.1-2 

Sarcopenia can be slowed through routine engagement in exercise, including strength or resistance training.3 Additionally, adequate intake of high-quality protein is required for the growth, and overall homeostasis of lean tissue.4 The Recommended Dietary Allowance (RDA) for protein and amino acids in adults is 0.8 g/kg body weight/day; this represents an estimate of adequate, average daily intake for 98% of the (healthy, general) population.4  Geriatric nutrition experts, however, posit that older adults may require more than the present RDA; in fact some have suggested that a protein intake of 1.2-2g/kg/day may be a more appropriate recommendation to help delay the sarcopenic process in older adults.2

It may, however, be difficult for aging adults to consume this amount of protein on a routine basis for a variety of reasons observed in the older adult population: reduction in overall energy intake (including protein), poor dentition, changes in food preferences, and a reduced ability to acquire and prepare food.5 Moreover, the elderly show a reduced ability to utilize protein as efficiently as younger adults, illustrating a blunted muscle protein synthesis (MPS) response to food intake including postprandial hyperaminoacidemia.6 Research indicates that this anabolic resistance may be overcome by increasing the intake of leucine, one of the three essential (must be consumed via diet and/or supplement) branched-chain amino acids (BCAAs).6

A single-blind, parallel-group study was conducted to assess leucine’s impact on myofibrillar protein synthesis (myoPS), the rate at which protein is being made in muscle tissue, comparing the effects of two protein beverage supplements:6

  • Lower protein + leucine: 10g of milk protein plus an additional 3g of L-leucine – “LEU” group
  • Higher protein with leucine: 25g of whey protein isolate (WPI) containing 3g of L-leucine – “WPI” group

Twenty-two healthy females (average age: 69) were randomly assigned to LEU or WPI groups and consumed their respective supplement BID for 6 days.6 Additionally, participants were asked to engage in unilateral leg resistance exercise during the study to determine the impact of the supplement both with and without resistance exercise. MyoPS was measured in the fasting and supplemented states as well as in the non-exercised and exercised states.6

The results of this study6 show that compared to a fasting state, acute (hourly) myoPS increased with the LEU supplement in the non-exercised leg (↑45%) and exercised leg (↑71%). In the WPI group, acute myoPS also increased in both the non-exercised leg (↑29%) and exercised leg (↑47%). Additionally, compared to the rested leg, acute myoPS was greater in the exercised leg with LEU (↑58%) and WPI (↑63%). Lastly, integrated (daily) myoPS increased similarly with WPI (↑9%) and LEU (↑9%) supplementation in the exercised leg, but only with WPI supplementation in the non-exercised rested leg.

In healthy older women, leucine supplementation added to a low dose of milk protein (10g) increased acute and daily protein muscle synthesis similar to a higher-protein whey protein isolate (25g).6 Exercise incrementally increased the muscle protein synthesis effect of leucine supplementation in healthy older women.6

Why is this Clinically Relevant?

  • Sarcopenia is a risk factor for loss of mobility and independent living and increases the risk of chronic disease
  • Sarcopenia can be slowed through routine resistance and strength training combined with adequate intake of protein, both in quantity and quality
  • Protein supplements with added leucine may be a prudent approach to mitigate skeletal muscle loss in aging women6
  • Clinicians can cater to each patient’s individualized protein needs and consider supplementation when appropriate

View the abstract


  1. Wolfe RR. The role of dietary protein in optimizing muscle mass, function and health outcomes in older individuals. Br J Nutr. 2012;108(Suppl 2):S88-93.
  2. Baum JI, Kim IY, Wolfe RR. Protein consumption and the elderly: what is the optimal level of intake? Nutrients. 2016;8(6):359. 
  3. Law T, Leatha AC, Clark BC. Resistance exercise to prevent and manage sarcopenia and dynapenia. Annu Rev Gerontol Geriatr. 2016;36(1):205–228.
  4. Dietary Reference Intakes for Energy, Carbohydrate. Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2002/2005).
  5. Volpi E, Campbell WW, Dwyer JT, et al. Is the optimal level of protein intake for older adults greater than the recommended dietary allowance? J Gerontol A Biol Sci Med Sci. 2013; 68(6): 677–681.
  6. Devries MC, McGlory C, Bolster DR, et al. Leucine, not total protein, content of a supplement is the primary determinant of muscle protein anabolic responses in healthy older women. J Nutr. 2018;148(7):1088-1095.


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