The benefits of a moderate to high protein intake in the diet are well documented, with current guidelines for athletes being 1.2-1.7g per kilogram of body mass/day (Rodriguez, 2009). However more recently this has been referred to as an over simplification and that recommending a daily protein intake is far more complex (Tipton & Witard, 2007).
Many people’s dietary intake of protein is inadequate in both quantity and timing. Muscle protein synthesis (MPS) is a complex balance between the source, pattern and timing of protein intake (Tipton & Witard, 2007). For example, it has been shown that in healthy young resistance trained men 20g of whey protein supplementation stimulates MPS as much as 40g of whey protein (Moore et al, 2009). It has also been established that on a meal by meal basis 20g of protein produces maximal MPS (Witard et al, 2014).
So the question remains what protein source is best? There are currently so many options, but if we examine the physiology the evidence starts to become more clear.
Proteins are made up of amino acids, there are 9 essential amino acids and 11 non-essential amino acids (Wolfe, 2017). Essential Amino Acids (EAA’s) refer to those which the body cannot produce and must be taken in from an outside source (Wolfe, 2017). These EAA’s can also be used to produce the other non-essential amino acids (Wolfe, 2017).
This essay will review the role of EAA mixes as a dietary protein supplement in comparison with other sources.
Muscle protein is in a constant state of turnover, with new protein being formed as old protein is being degraded (Wolfe, 2017). For muscle growth to occur muscle protein synthesis must exceed muscle protein breakdown (Wolfe, 2017). Muscle protein synthesis requires an abundant availability of all 9 essential amino acids, whereas a shortage of non-essential amino acids can be compensated for by increased de novo production (Wolfe, 2017).
When plasma EAA levels fall EAA’s are released from muscle to ensure adequate protein supply for other tissues – this is a catabolic state. Muscles have been referred to as a reservoir of EAA’s for the rest of the body to use as required (Wolfe, 2017). Endogenous stores of plasma and free EAA’s are small and therefore the muscles will readily be required to supply EAA’s for other tissues (Wolfe, 2017).
Therefore, supplementation of an imbalanced mixture of amino acids which does not contain all 9 essential amino acids will only be able to sustain transient MPS by utilizing endogenous stores of the other EAA’s required for MPS (Wolfe, 2017). Therefore, theoretically at least it is not possible for unbalanced supplements such as BCAA’s to stimulate MPS other than for a short transient period (Wolfe, 2017).
EAA supplementation, has been demonstrated to be as effective as whey protein at MPS in young populations, but more effective in older populations (Pasiakos et, al, 2011). The addition of leucine to an EAA mix further enhances the MPS potential (Pasiakos et al, 2011). Leucine is well known to enhance MPS by stimulating the mammalian target of rapamycin pathway, but sustained MPS requires all 9 essential amino acids (Crozier et, 2005). It has also been shown that the addition of carbohydrate to a leucine enhanced EAA mix does not further increase MPS (Crozier et al, 2005).
EAA Supplementation and Sarcopenia
A very concerning medical condition which is gaining increased attention in recent years is sarcopenia, or age related muscle loss. Muscle mass loss occurs at a rate of ~1%/y in men and ~0.5%/y in women beyond the age of 50 y (Wilkinson et al, 2017). Sarcopenia has been causally linked to metabolic syndrome, type 2 diabetes, osteoporosis, a lower quality of life and increased aging (Wilkinson et al, 2017). With an aging population this is becoming a major public health concern (Wilkinson et al, 2017).
Numerous protein supplements have been proposed to help prevent sarcopenia, however it also has to be remembered that older people may have a poorer absorption of protein and a reduced ability to break down whole proteins. Therefore, readily absorbable forms are more beneficial. Additionally, in older people a greater plasma amino acid spike is required to stimulate MPS, therefore a more readily absorbed form will be more beneficial.
EAA Supplementation and Cholesterol
A supplement of 44% leucine and 54% EAA has been shown to decrease plasma triglyceride concentrations by 20% and intrahepatic lipid by 50% in 16 weeks, this is equivalent or greater than the pharmaceutical drug Fenofibrate and was also independent of other diet or exercises changes (Coker et al, 2015).
EAA Supplementation and Insulin Resistance
In a further study the addition of 2g plant sterols produced benefits in reduced risk factors for metabolic syndrome, including increased insulin sensitivity in 4 weeks (Coker et al, 2015).
EAA Supplementation and Young Adults
As little as 6g of EAA supplementation was also found to increase muscle protein synthesis by 3.5-fold when it was given along with 35 g of carbohydrate after resistance exercise (Børsheim et al, 2002).
Journal of the International Society of Sports Nutrition concluded that post-exercise ingestion of EAAs, have been shown to stimulate robust increases in muscle protein synthesis with or without added carbohydrates (Kerksick et al, 2008 & Pasiakos et al, 2011).
In summary from this brief review essential amino acids appear to be very beneficial form of protein supplementation providing all the required amino acids, and producing very little waste produce. It can be concluded that EAA mixes are the cleanest form of protein supplementation ideal for use in all populations.
Børsheim, E., Tipton, K. D., Wolf, S. E., & Wolfe, R. R. (2002). Essential amino acids and muscle protein recovery from resistance exercise. American Journal of Physiology-Endocrinology and Metabolism, 283(4), E648-E657.
Coker, R.H., Deutz, N.E., Schutzler, S., Beggs, M., Miller, S., Wolfe, R.R. and Wei, J., 2015. Nutritional supplementation with essential amino acids and phytosterols may reduce risk for metabolic syndrome and cardiovascular disease in overweight individuals with mild hyperlipidemia. Journal of endocrinology, diabetes & obesity, 3(2).
Crozier SJ, Kimball SR, Emmert SW, Anthony JC, Je erson LS (2005) Oral leucine administration stimulates protein synthesis in rat skeletal muscle. J Nutr 135:376–382
Kerksick, C., Harvey, T., Stout, J., Campbell, B., Wilborn, C., Kreider, R., ... & Ivy, J. L. (2008). International Society of Sports Nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition, 5(1), 17.
Pasiakos SM et al (2011) Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances post exercise muscle protein synthesis. Am J Clinical Nutrition 94:809–818.
Rodriguez, N.R., Di Marco, N.M. & Langley, S. (2009). American College of Sports Medicine position stand. Nutrition and athletic performance. Medicine and Science in Sports and Exercise, 41, 709-731.
Tipton, K.D. & Witard, O.C. (2007). Protein requirements and recommendations for athletes: relevance of ivory tower arguments for practical recommendations. Clinical Sports Medicine, 26, 17-36.
Wilkinson, D. J., Bukhari, S. S., Phillips, B. E., Limb, M. C., Cegielski, J., Brook, M. S., ... & Lund, J. (2017). Effects of leucine-enriched essential amino acid and whey protein bolus dosing upon skeletal muscle protein synthesis at rest and after exercise in older women. Clinical Nutrition.
Witard, O.C. et al. (2014). Myo brillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise. American Journal of Clinical Nutrition, 99, 86-95.
Wolfe, R.R., 2017. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?. Journal of the International Society of Sports Nutrition, 14(1), p.30.