ENC likes to provide the opportunity for up and coming investigators to showcase their research, and today’s post comes from a student of Jamie I. Baum, PhD, Assistant Professor of Nutrition at the University of Arkansas. Brianna L. Neumann graduated from Truman State University with a bachelor of science in Exercise Science. Her undergraduate research experience involved sports nutritional research, which began her desire to continue her education to focus on protein’s metabolic effect in the body. She currently is a Master’s student at the University of Arkansas in the Department of Food Science, where her research specifically focuses on the impact protein quality and quantity on whole body energy metabolism.
In today’s society, big muscles are associated with weight lifting, men and sports. However, for most people, the benefits of gaining muscle mass include improvement in gross motor skills and a potential decrease in sarcopenia (gradual age-related loss in muscle mass and function). When discussing the building of muscle mass, a term you need to be familiar with is muscle protein synthesis (MPS). In general, in order to gain muscle mass, you need to synthesize more muscle than your body is breaking down. Through extensive research on muscle mass, it is known that an outside stimulus, such as resistance exercise, is required for building muscle. More recently, it has been discovered that nutrition, specifically in the form of protein, also plays a vital role in the physiology of this process5, 6.
Research has shown that consumption of high-quality proteins (e.g. beef; eggs) can stimulate MPS in both young and elderly individuals, following a meal8, and this effect may be attributed particularly to the quality – not just the quantity – of the protein. High-quality proteins tend to be from animal sources and include eggs, poultry, beef and dairy, which are high in essential amino acids (EAA), particularly the branched-chain amino acid leucine. Data show that leucine promotes MPS at a greater rate than that of the other EAA due to leucine’s ability to activate the mammalian target of rapamycin (mTOR), the key regulatory pathway in MPS1, 3.
A recent study clearly demonstrates the relationship between EAA and MPS. Eight individuals were given 10 grams of EAA on two separate occasions and a dose of rapamycin (an inhibitor of mTOR) on one occasion, which led to a 60% increase in MPS following ingestion of EAA. However, this effect was completely blocked when subjects were treated with rapamycin4. In addition, another study tested 8 healthy, sedentary older adults with diets supplemented by leucine for 2 weeks (4 grams per meal) and found a significant increase in muscle fractional synthesis rate at the end of the treatment period4. The muscle fractional synthesis rate is the fraction of the proteins that are synthesized in the muscle per unit of time9.
Resistance exercise can also increase MPS and add “bulk,” or increase muscle mass. There are two primary principles of exercise that need to occur in order for someone to successfully add “bulk”: progression and overload. The most important for MPS is overload, defined as placing additional stress on a muscle above normal conditions, and includes exercises such as weight lifting and swimming. Therefore, in order for someone to “bulk up,” they must have an outside stimulus that serves to initiate MPS inside the body. There are various ways to achieve overload such as adding more weight or increasing a swimming distance, and research is still being done regarding how to maximize MPS. A recent study examined the effect of concentric resistance exercise on 8 trained men2 to determine if muscle building signaling enzymes were progressively increased as more sets of resistance activity were performed. The investigators concluded that performing additional sets showed a greater increase in MPS than just a single set of lifts.
Is there an additive effect of protein ingestion and resistance exercise? As stated above, both exercise and nutrition initiate MPS, and ideally, one would have both in order to maximize muscle building within the body. For example, the effect of beef ingestion coupled with resistance exercise was recently tested in 35 middle-aged men who consumed one of four different amounts of beef (0, 57, 113 and 170 grams) prior to resistance exercise (unilateral movements). Results of this study demonstrated that eating 170 grams of beef in addition to exercise significantly elevated MPS when compared to the other groups7.
In summary, MPS is complex and can be influenced by both nutrition and exercise. Both can activate MPS individually, but research shows combining the two is best to promote MPS. Further research is still needed to understand the long-term impact of this combination, as well as the practicality of dietary intake for individuals in order to maintain and increase muscle tissue.
- Anthony JC, Yoshizawa F, Anthony TG, Vary TC, Jefferson LS, Kimball SR. Leucine stimulates translation initiation in skeletal muscle of postabsorptive rats via rapamycin sensitive pathway. Journal of Nutrition. 2000; 130(10): 2413-9.
- Burd NA. Holwerda AM, Selby KC, West DW, Staples AW, Caine NE, Cashaback JG, Potvin JR, Baker SK, Phillips SM. Resistance exercise volume affects myofibrillar protein synthesis and anabolic signaling molecule phosphorylation in young men. Journal of Physiology. 2010; 588(Pt 16): 3119-30.
- Caperson SL, Shelffield-Moore M, Hewlings SJ, Paddon-Jones D. Leucine supplemenatation chronically improves muscle protein synthesis in older adults consuming the RDA for protein.Clinical Nutrition. 2012; 31(4): 512-519.
- Dickson JM, Fry CS, Drummond MJ, Gundermann DM, Walker DK, Glynn EL, Timmerman KL, Dhanani S, Volpi E, Rasmussen BB. Mammalian target of rapamycin complex 1 activation is required for the stimulation of human skeletal muscle protein synthesis by essential amino acids.The Journal of Nutrition. 2011; 141(5): 856-62.
- Drummond MJ, Rasmussen BB. Leucine-enriched nutrients and the regulation of mammalian target of rapamycin signaling and human skeletal muscle protein synthesis. Current Opinion in Clinical Nutrition and Metabolic Care. 2008; 11(3): 222-6.
- Millward DJ, Layman DK, Tomé D, Schaafsma G. Protein quality assessment: impact of expanding understanding of protein and amino acid needs for optimal health. American Journal of Clinical Nutrition. 2008; 87 (5): 1576S-1581S.
- Robinson MJ, Burd NA, Breen L, Rerecich T, Yang Y, Hector AJ, Baker SK, Phillips SM. Does-dependent responses of myofibrillar protein synthesis with beef ingestion are enhanced with resistance exercise in middle-aged men. Applied Physiology, Nutrition, and Metabolism. 2013; 38 (2): 120-5.
- Symons TB, Sheffield-Moore M, Wolfe RR, Paddon-Jones D. A moderate serving of high quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects.Journal of American Dietetics Association. 2009; 109(9):1582-6.
- Wolfe RR. Skeletal muscle protein metabolism and resistance exercise. The Journal of Nutrition. 2006; 136(2): 525S-528S.