Literature Review on the Benefits of Protein Supplementation for Muscle Hypertrophy

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1 Literature Review on the Benefits of Protein Supplementation for Muscle Hypertrophy Item Type text; Electronic Thesis Authors Mahdi, Layth Mithim Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 20/06/ :39:38 Link to Item

2 LITERATURE REVIEW ON THE BENEFITS OF PROTEIN SUPPLEMENTATION FOR MUSCLE HYPERTROPHY By LAYTH MITHIM MAHDI A Thesis Submitted to The Honors College In Partial Fulfillment of the Bachelors degree With Honors in Physiology THE UNIVERSITY OF ARIZONA M A Y Approved by: Dr. Douglas Keen Department of Physiology

3 Abstract The debate of whether protein supplementation in addition to that of diet is of any benefit is still on going as there are seemingly equivocal studies on both sides. This literature review attempts to examine the current studies and to find a pattern and a potential answer to this question. After looking at protein supplementation for the elderly and the active, the type of protein and the timing of the supplementation, it is concluded that the protein supplementation is most likely of no major benefit as long the individual is getting enough protein from diet. The timing of the supplementation is likely not nearly as important as the total protein intake. In addition, the RDA seems to be inadequate for the active and the elderly so it is of importance to continue conducting further studies to find an appropriate RDA range of protein for different population demographics. Introduction Engrained into mainstream bodybuilding and weightlifting culture is the importance of protein supplementation of one s daily needs to maximize muscle hypertrophy, strength and recovery. The supplement industry is massive with protein powder alone generating 5.6 billion dollars in sales worldwide during 2013 (Statista). Protein supplementation for the purposes of reaching the recommended daily allowance (RDA) of 0.8g protein/kg of bodyweight/day is of clear health benefit as amino acids are essential for the maintenance and growth of muscle. This is especially true for demographics such as growing children and pregnant women who may not being receiving the RDA of protein. However, there is much debate about whether additional supplementation past the RDA is beneficial. Athletes and those with active lifestyles often rely on protein supplementation as a way of enhancing performance and muscle hypertrophy even though they are receiving the RDA of protein from their diet. If in fact additional protein

4 supplementation has no benefit, then a large portion of this multibillion dollar industry would have no scientific basis. The purpose of this literature review will be to analyze current and past research to attempt to determine whether protein supplementation is of any benefit for muscle hypertrophy or potentially whether the RDA is sufficient. Skeletal muscle cells are made up of bundles of myofibrils. These myofibrils are composed of units of sarcomeres, each made up of thick filaments (myosin protein) and thin filaments (actin protein). There are other important proteins such as troponin found throughout the sarcomeres. Simply based off structure, it is clear that proteins and amino acids are inherent to the function and growth of muscle cells. Although resistance training does not lead to the formation of new muscle cells, the individual cells themselves can hypertrophy (increased crosssectional area). This occurs when resistance training results in micro-tears in muscle cells and injury to their organelles. This injury activates satellite cells and causes them to proliferate at the injury site. The satellite cells fuse to the muscle fibers, some forming organelles on the muscle fiber while the majority differentiate to form new myofibrils (in addition to repairing the tears) (sub Kwon, & Kravitz, 2017). The new myofibrils increase the cross-sectional area of the muscle fiber (increasing contraction force). In addition, some of the fused satellite cells contribute new nuclei. These new nuclei allow the muscle fiber to synthesize more contractile proteins (actin and myosin). The process of repairing and growing these muscles is heavily dependent on proteins and amino acids. Thus, the amount of protein ingested by diet and the total amount of amino acids in the body at any one time is also crucial to muscle hypertrophy (sub Kwon, & Kravitz, 2017). The digestion and absorption of ingested proteins first begins in the stomach. The gastric mucosa is stimulated by the entry of protein to release gastrin. Gastrin is a hormone which

5 stimulates chief cells to secrete pepsinogen and parietal cells to secrete HCl. HCl creates the acidic environment of the stomach which activates pepsinogen by causing it to unfold and cleave itself to become the active protease pepsin. The acidic environment of the stomach also denatures and unfolds the proteins exposing the peptide bonds to hydrolysis by pepsin. The ingested proteins can then be broken down into smaller peptides (Mehta, 2017). Next, the peptides enter the small intestine. When HCl enters from the stomach into the duodenum of the small intestine, the hormone secretin is released into the blood. The acinar cells of the pancreas are stimulated to release water and bicarbonate by secretin. The bicarbonate neutralizes the acidic ph to about 7. This is important for the purposes of preventing HCl and the acidic environment in the stomach from denaturing enzymes in the small intestine (Britannica). As the peptides move through the small intestine, the hormone cholecystokinin is activated and causes the release of zymogens (chymotrypsinogen, trypsinogen and procarboxypeptidase A and B) from the pancreas. Enteropeptidases convert trypsinogen to trypsin which then converts the other zymogens (including trypsinogen) into their activated enzymatic form. The various enzymes are specific for different amino acids and types of peptide bonds. This results in the conversion of the ingested peptides to free amino acids (Mehta, 2017). These free amino acids are transported across the apical surface of the intestinal mucosa. This is done via sodium-amino acid transporters. Next, the free amino acids enter the bloodstream to be transported to the liver, muscle and other cells throughout the body. (Anatomy and Physiology). How the body uses the dietary amino acids is dependent on the nitrogen balance. A positive nitrogen balance, where the intake of nitrogen (i.e. amino acids) is higher than the excretion of nitrogen, is required for muscle hypertrophy. When carbohydrates and fats are not meeting the body's energy needs (i.e. in a state of fasting), protein and amino acids will be used

6 for energy. One way this can happen is by degrading muscle protein into alanine which is converted to pyruvate in the liver. The pyruvate can be used in gluconeogenesis to produce glucose that fuels aerobic and anaerobic metabolism. Thus, it is important to maintain a positive nitrogen balance and to make sure the rest of the body's energy needs are being met to allow for maximal muscle hypertrophy (McKenzie, 2017). If we begin to look at studies concerning protein supplementation we come across varied and contradictory conclusions. This is not necessarily to be unexpected if we take into account the complexity of the human metabolism and all the mechanical and chemical factors of exercise. To the best of my ability, I will aim to summarize a diverse range of articles in order to find any connections or patterns between both similar and dissimilar conclusions. Review and Analysis I will begin with a group of studies that focus on protein supplementation and muscle hypertrophy in the elderly. Even though the main purpose of this literature review is to focus on those looking to increase muscle hypertrophy for athletic reasons, I believe that looking at aging will prove beneficial. It is well known that humans naturally lose muscle strength and mass as they age (Wolfe, 2008). One particular review found that there is consistent evidence that an increase in protein consumption for the elderly from the RDA of 0.8 g/kg/day to g/kg/day combined with resistance exercise will reduce age-related muscle mass loss (Nowson, 2015). This increased RDA is similar to that of those who are active (Phillips, 2006). I will compare these findings to studies that look at protein supplementation for athletes and analyze various factors including both amount of protein and the timing of the supplementation. One study conducted on healthy elderly men and women attempted to find out whether or not protein supplementation aided the adaptive response to prolonged resistance-type exercise

7 training (Leenders, 2013). In this study, 31 elderly men and 30 elderly women with an age of 70 +/- 1 years participated in resistance training over 24 weeks. They were randomly assigned to take additional protein supplementation (15g/day) or a placebo. The participants continued their own habitual dietary regimen but were asked to record their dietary intake records. As such it was found that women had an average of 1.2 +/- 0.1 g/kg/day of protein while men had an average of 1.1 +/- g/kg/day of protein (including the protein from supplementation). At the end of the study, leg muscle mass, quadriceps cross-sectional area, type II muscle fiber size, and sitto-stand improved similarly in the placebo group as the group that took the additional protein supplementation. This study does indeed confirm the benefits of resistance training for the elderly but indicates no benefits to taking a protein supplement (Leenders, 2013). Another similar study was conducted with 26 health elderly men (age 72+/- 2 years) who were randomly assigned to a progressive, 12-wk resistance-type exercise training program with (protein group) or without (placebo group) protein given before and after each exercise session (Verdijk, 2009). In this study, the participant s personal dietary regimen was also recorded and found that both the protein and placebo group had an average of 1.1 +/- 0.1 g/kg/day (excludes given protein supplementation). Muscle hypertrophy was assessed and it showed similar increases in leg muscle mass and quadriceps mass for both groups. Type I muscle hypertrophy was greater than type II but there was no significant difference between the two groups. This study once again shows the benefits of resistance training for the elderly but shows no significant benefit for additional protein supplementation. However, it should be noted for both these studies the average protein received from the diet was higher than the RDA of 0.8 g/kg/day (around 1.1 +/- 1 for most participants). This is consistent with the review from Nowson which showed a

8 decrease in age related muscle loss when combined with an increase in the RDA of protein from 0.8 to g/kg/day. A third study conducted on 65 frail elderly subjects attempted to assess the impact of 24 weeks of dietary protein supplementation on muscle mass, strength, and physical performance (Tieland, 2012). In this study, frailty was defined as a geriatric syndrome of decreased reserves and resistance to stressors that result in an increased of adverse outcomes, such as onset disability, morbidity, institutionalization, and mortality with sarcopenia (loss of skeletal muscle mass, strength and physical performance related to age) being a fundamental component of frailty. The participants were randomly assigned to a placebo supplementation (7.1g lactose, 0.5g fat, and.4g calcium) or a daily protein supplementation (the same with an additional 15g protein) which was given after breakfast and after lunch. The participants recorded their dietary intake and both the placebo and protein group were found to have an average protein intake of 1.0+/- 0.1 g/kg/day (excluding additional protein supplementation). Those in the protein supplementation group had in increase of ~1.0 to 1.4 g/kg/day of protein with no significant difference of fat and carbohydrates between the groups. The study found there was no change in skeletal muscle mass but there was a significant increase in muscle strength in both groups. However, leg extension strength increased from 57+/-5 to 68+/5 kg in the protein group which is more than the increase in the placebo group (57+/-5 to 63+/-5 kg). The protein group also experienced a significant increase in physical performance while the placebo group had no change. Overall, this study does show that additional protein supplementation resulted in increased muscle strength and performance (although no increase in muscle mass). This study is different from the previous two in that the subjects did not undergo resistance training. In addition, these results are at odds with the results of the previous two studies. The possible

9 reasons for this discrepancy is most likely related to the frail conditions of the participants and their sarcopenia. It is likely that these participants needed an increase in dietary protein as they were losing muscle faster than the other groups. This is evident by the fact that there seemed to be an increased need for nutrients overall due to the placebo group showing an increase in muscle strength even without the protein supplementation (just with the lactose, fat, and calcium supplementation). Just as the RDA for dietary protein should likely be higher for the elderly (Nowson, 2015), this study indicates that those who are frail would likely need even more protein in their diet. To analyze the use of protein supplementation for a younger demographic, we can begin by looking at a study that was designed to examine the effects of colostrum and a protein blend on muscle strength and morphology changes after four weeks of resistance training in untrained men (Boone-Medicine and Science, 2015). The participants were 27 untrained men with an average age of 22 +/- 2.5 years who were randomly assigned to one of 3 groups. The first group was a protein group where they were given colostrum (3g), whey protein (17g), and leucine (2g). The second group was a colostrum group where they were given just colostrum (3g) and the third group was given a placebo. There was no information present about the diets of the participants so the average dietary protein intake is unavailable. After four weeks of resistance training, there was increased muscle strength, muscle size and pennation angle for all participants with no significant differences between the groups. These results indicate that there is no benefit of protein supplementation for this young demographic, though more detailed analysis is difficult without information about the participants daily dietary regimen. A similar study was done by the same group but instead with 18 untrained men (age of 22 +/- 2.5 years) who trained for 4 weeks (Boone-Applied Physiology, 2015). The participants were

10 split into 2 groups with one group given colostrum (3g), whey protein (17g), and leucine (2g) and the other given a placebo post-exercise. The analysis of the dietary regimen found no significant difference between the groups in carbohydrates, fat, protein or relative protein intake at testing. At the end of the training period, it was found that both groups experienced similar improvements in performance and muscle morphology, once again indicating that protein supplementation did not have any additional benefits. If we look at a couple of studies that include a comparison of dairy based whey protein supplementation and a soy based protein supplementation, we find some results that show a benefit to protein supplementation to lean body mass gains. One study found that whey protein is more effective than soy protein at increasing lean body mass gains during resistance training (Volek, 2012). The whey protein group had an average increase of 3.3+/- 1.5 kg, the soy protein group had an increase of 1.8 +/- 1.6 kg and the carbohydrate group had an increase of 2.3+/- 1.7 kg of lean muscle mass. The study ensured that the participants had a standard protein intake of 1.0 to 1.2 g/kg/day (excluding the supplements). Thus, these results show the benefit of protein supplementation and the importance of protein quality [whey protein] as an important determinant of lean body mass responses to resistance training (Volek, 2012). Another study compared a whey protein supplement, a blend of soy-dairy protein supplement and a placebo during resistance exercise training (Reidy, 2017). The results of this study concluded that protein supplementation had a modest effect on whole body lean mass as compared to the placebo. In addition, there was no difference between the two protein types. This study correlates with the Volek study in showing the beneficial effects in lean body mass gains. However, the results did not corroborate with the previous study as it showed no effect between the two protein types. Although, it must be noted the Reidy study compared a blend of soy-dairy vs whey rather than

11 the soy vs whey the Volek study tested. In addition, the study by Reidy goes further to test myofibril hypertrophy, satellite content and myonuclear addition and concluded that protein supplementation did not enhance any of these factors. Although there may be benefit to protein supplementation in lean body mass gains, there does not seem to be a benefit in the actual hypertrophy of the muscle and thus Reidy proposes that as long as protein intake is adequate during muscle overload the adaptations in muscle growth and function will not be influenced by protein supplementation. It is also important to examine the importance of timing in the ingestion of the protein supplementation. A review focusing on the effect of creatine or protein supplementation during resistance training in the elderly found that protein ingestion before exercise sessions offers a small advantage, possibly through increased amino acid delivery to muscle owing to exerciseincreased blood flow (Candow, 2008). This review indicates that the timing of the supplementation may be more important than the absolute daily intake (Candow, 2008). However, this conclusion is in disagreement with a more recent meta-analysis that concluded that with respect muscle strength and hypertrophy, total protein intake was the strongest predictor (Schoenfeld, 2013). This conclusion refutes the commonly held belief that the timing of protein intake in and around a training session is critical to muscular adaptations and indicate[s] that consuming adequate protein in combination with resistance exercise is the key factor for maximizing muscle protein accretion (Schoenfeld, 2013). This analysis concludes that the perceived hypertrophic benefits seen in timing studies is likely a result of the increased consumption of protein rather than the timing of the supplementation. It also concludes that most likely a protein consumption of at least 1.6 g/kg/day is necessary to maximize muscle protein accretion in individuals involved in resistance training programs (Schoenfeld, 2013).

12 Conclusion Although the question of the benefits of protein supplementation seems rather simple, we can see there are many factors to consider and many more conflicting studies that try to address these factors. From this analysis, the overall trend indicates that the key to muscle hypertrophy and muscle strength increase is adequate protein intake. The issue seems to lie with how one defines what is the adequate protein intake and the troubles with trying to have one or even two recommended daily allowances for the entire population. Each body and situation is different and thus are its individual needs. The literature seems to lean in the direction that protein supplementation is of no great benefit if one is getting enough protein in their diet. The RDA of protein of 0.8 g/kg/day may be appropriate for a sedentary individual, but would most likely be much higher for the elderly and for those who are active. An appropriate RDA of protein for the elderly would likely need to be around g/kg/day to help combat the age-related muscle loss (Nowson, 2012) and possibly even higher with those who are frail (Tieland, 2012). Further studies need to be conducted to confirm that the benefit is due to the protein and not just the caloric increase (at least in the frail elderly) as well as attempt to find a more exact RDA range. For someone who is active and engages in resistance training, a similar increase in RDA of protein is needed of around g/kg/day (Schoenfeld, 2013). Protein supplementation itself is likely only of benefit when this elevated RDA is not met through diet. Even then, the timing of the supplementation is still not nearly as important as the total intake of the protein (Schoenfeld, 2013). Further studies are needed to confirm the lack of importance of the timing and to confirm or find a more exact RDA range.

13 Citations 1) Global sports nutrition protein product sales by category, 2013 Statistic. (2017). Statista. Retrieved 1 January 2017, from 2) Sub Kwon, Y., & Kravitz, L. (2017). How Do Muscles Grow?. Unm.edu. Retrieved 1 January 2017, from 3) Mehta, S. (2017). Digestion of Dietary Proteins in the Gastro-Intestinal Tract (GI tract) Biochemistry Notes PharmaXChange.info. PharmaXChange.info. Retrieved 1 January 2017, from gastro-intestinal-tract-gi-tract/ 4) Anatomy and Physiology. (2017). Philschatz.com. Retrieved 1 January 2017, from 5) McKenzie, L. (2017). Metabolism: Nitrogen - Fastbleep. Fastbleep.com. Retrieved 1 January 2017, from 6) Wolfe, R., Miller, S., & Miller, K. (2008). Optimal protein intake in the elderly. Clinical Nutrition, 27(5), ) Nowson, C., & O'Connell, S. (2015). Protein Requirements and Recommendations for Older People: A Review. Nutrients, 7(8), ) Phillips, S. (2006). Dietary protein for athletes: from requirements to metabolic advantage. Applied Physiology, Nutrition, And Metabolism, 31(6),

14 9) LEENDERS, M., VERDIJK, L., VAN DER HOEVEN, L., VAN KRANENBURG, J., NILWIK, R., & WODZIG, W. et al. (2013). Protein Supplementation during Resistance- Type Exercise Training in the Elderly. Medicine & Science In Sports & Exercise, 45(3), ) Verdijk, L., Jonkers, R., Gleeson, B., Beelen, M., Meijer, K., & Savelberg, H. et al. (2009). Protein supplementation before and after exercise does not further augment skeletal muscle hypertrophy after resistance training in elderly men. American Journal Of Clinical Nutrition, 89(2), ) Tieland, M., van de Rest, O., Dirks, M., van der Zwaluw, N., Mensink, M., van Loon, L., & de Groot, L. (2012). Protein Supplementation Improves Physical Performance in Frail Elderly People: A Randomized, Double-Blind, Placebo-Controlled Trial. Journal Of The American Medical Directors Association, 13(8), ) Boone, C., Beyer, K., Stout, J., Hoffman, J., Fragala, M., & Fukuda, D. (2015). Training- Induced Muscle Strength and Hypertrophy Occur Independently of Protein Supplementation in Untrained Young Men. Medicine & Science In Sports & Exercise, 47, ) Boone, C., Stout, J., Beyer, K., Fukuda, D., & Hoffman, J. (2015). Muscle strength and hypertrophy occur independently of protein supplementation during short-term resistance training in untrained men. Applied Physiology, Nutrition, And Metabolism, 40(8), ) Volek, J., Volk, B., Gómez, A., Kunces, L., Kupchak, B., & Freidenreich, D. et al. (2013). Whey Protein Supplementation During Resistance Training Augments Lean Body Mass. Journal Of The American College Of Nutrition, 32(2),

15 15) Reidy, P., Fry, C., Igbinigie, S., Deer, R., Jennings, K., & Cope, M. et al. (2017). Protein Supplementation Does Not Affect Myogenic Adaptations to Resistance Training. Medicine & Science In Sports & Exercise, 1. 16) Schoenfeld, B., Aragon, A., & Krieger, J. (2013). The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal Of The International Society Of Sports Nutrition, 10(1), ) Candow, D., & Chilibeck, P. (2008). Timing of creatine or protein supplementation and resistance training in the elderly. Applied Physiology, Nutrition, And Metabolism, 33(1),

16 Informational pamphlet based on the review: Protein Supplementation: Is it necessary? How much protein should I get per day? If you are sedentary (don t play sports or workout often) then 0.8 g/kg/day is an appropriate amount. o You can calculate this by multiplying your weight in kilograms by 0.8g. o You can convert from your weight in pounds to kilograms by dividing by 2.2. If you are active (play sports or workout often) then somewhere around g/kg/day is an appropriate amount. o You can calculate this by multiplying your weight in kilograms by 1.3g up to 1.6g. Should I take a protein supplementation? If you can track your protein intake throughout the day and find that you are getting an appropriate amount that it is likely unnecessary to take a protein supplementation. If you are unable to meet your required protein intake from diet, then a protein supplementation may be a good idea.