Protein: the Right Dose for Maximum Muscle Growth

By Michael J. Rudolph, Ph.D.

Greater dietary protein consumption drives muscle anabolism well beyond acknowledged limits, by powerfully preventing muscle protein breakdown and promoting tremendous gains in size and strength.

The anabolic response within muscle, or net gain in muscle protein, is the difference between the rates of muscle protein synthesis versus muscle protein breakdown where greater protein synthesis produces muscle growth. This anabolic response can be increased considerably by dietary protein consumption, which stimulates muscle protein synthesis and decreases muscle protein degradation.¹ Several studies, including one by Symons et al.², indicate that the maximum stimulation of muscle protein synthesis occurs with intake of 20-30 grams of protein per meal. This conclusion eventually drove the concept that there is a maximal anabolic response to protein intake, and consuming more than 20-30 grams of protein per meal will most likely exceed the maximally effective intake of protein on the anabolic response.³ However, according to more recent research, this interpretation relies too heavily on protein consumption’s influence on muscle protein synthesis while not putting enough importance on muscle protein breakdown. One of the primary reasons for this misconception is that experimentally measuring muscle protein breakdown is rather difficult, requiring much more complicated experimental protocols.⁴ Taking this fact into account, recent scientific data simultaneously measuring both muscle protein synthesis and breakdown suggests that the ability of protein consumption to reduce muscle protein breakdown may be much larger than originally thought, contributing to much greater levels of muscle protein accumulation for considerably greater muscle size. 

Limited Influence on Muscle Protein Synthesis

As previously mentioned, protein turnover in the muscle cell is a complex process that encompasses both protein synthesis and protein breakdown of existing muscle protein. Increasing muscle mass arises, in part, from a greater amount of muscle protein synthesis. Protein or amino acid consumption achieves greater muscle protein synthesis by activating the extremely important nutrient-sensing molecule mTOR, which stimulates muscle protein synthesis and increases muscle mass. This has clearly been shown in several studies, including one by Walker et al.⁵, which showed that ingesting essential amino acids increased mTOR activity – leading to greater muscle protein synthesis by an additional two hours, as compared to an exercised group that was not fed essential amino acids. Interestingly, this study also confirmed that consuming greater amounts of essential amino acids increased the cellular stockpile of amino acids stimulating muscle protein synthesis, but this stimulatory influence leveled off at 10 grams of essential amino acids per day. Additionally, another study by Moore et al. confirmed that protein intake of 20 grams immediately after lifting weights induces optimal muscle protein synthesis, with anything greater than 20 grams having no additional muscle-building effect.³

Preventing Muscle Protein Breakdown

Insulin is an extremely anabolic hormone that is released at an increased rate in response to ingestion of carbohydrate and certain proteins or amino acids. After secretion from the pancreas, insulin binds to the insulin receptor, setting off a cascade of signaling events that eventually activates the enzyme mTOR that directly activates muscle protein synthesis and prevents muscle protein breakdown.^6,7 Since muscle protein breakdown generates free amino acids, the ability of insulin to decrease muscle protein breakdown also reduces the amount of amino acids within the muscle cell. Unfortunately, this decrease in amino acid amount within muscle eventually precludes any positive influence that protein consumption has on muscle protein synthesis – creating a point where further protein consumption no longer promotes muscle protein synthesis. However, according to recent research^8-11, even at this point insulin continues to promote muscle growth because it can still potently suppress muscle protein breakdown. Therefore, insulin’s capacity to suppress muscle protein breakdown is presumably most important when considering how much protein to consume. This is especially true when protein is simultaneously consumed with carbohydrate, which induces an even greater insulin response than protein. That said, consuming higher levels of protein that were previously thought to be ineffective because the rate of muscle protein synthesis reached its peak should promote greater muscle growth – especially when consumed with carbohydrate, due to a greater insulin response that suppresses protein breakdown and enhances muscle growth.

While initially this observation seems questionable, results from a study by Bouillanne et al. clearly support this hypothesis.¹² In this study, test subjects consumed increasing amounts of protein, up to as high as 80 percent of their daily protein requirement in a single meal. Interestingly, while measuring net muscle protein synthesis they saw a linear increase in all subjects, even when they consumed 80 percent of their daily protein requirement. These results show that a maximal anabolic response was not reached even while consuming 80 percent of their daily protein requirement. Since muscle protein synthesis most likely peaked at protein consumption levels much lower than 80 percent of daily requirement, it must be the reduction in muscle protein breakdown that continues to provide an anabolic response. Moreover, several other studies^8-11 measuring muscle protein synthesis and breakdown confirm that this observation is correct even at very high protein intake – and most importantly, all of these studies show that greater protein consumption also increases muscle mass.

While these studies highlight an experimental flaw that sheds new light on protein consumption and muscle growth, obviously the linear relationship between protein intake and muscle growth seen in these studies will eventually level off. So the take-home message here seems to be that many of us have probably underestimated our protein consumption requirements, and an incremental increase in protein intake will in all likelihood elicit additional muscle mass and strength.

Gains in Size and Strength

In conclusion, although protein intake stimulates muscle protein synthesis and this contributes to muscle growth, protein consumption has an even greater influence on muscle size due to its ability to impressively reduce muscle protein breakdown. Moreover, because protein consumption has a limited influence on muscle protein synthesis, accepted nutritional guidelines based on this fact have erroneously concluded that there is also a maximal amount of protein intake for muscle protein breakdown. Recent evidence indicates that greater dietary protein consumption drives muscle anabolism well beyond acknowledged limits, by powerfully preventing muscle protein breakdown and promoting tremendous gains in size and strength.

For most of Michael Rudolph’s career he has been engrossed in the exercise world as either an athlete (he played college football at Hofstra University), personal trainer or as a research scientist (he earned a B.Sc. in Exercise Science at Hofstra University and a Ph.D. in Biochemistry and Molecular Biology from Stony Brook University). After earning his Ph.D., Michael investigated the molecular biological effects of exercise as a fellow at Harvard Medical School and Columbia University. That research contributed seminally to understanding the function of the incredibly important cellular energy sensor AMPK – leading to numerous publications in peer-reviewed journals including the journal Nature. Michael is currently a Senior Scientist working at the New York Structural Biology Center where he investigates the molecular nature of human illness and disease.

References:

1. Hawley JA, Gibala MJ and Bermon S. Innovations in athletic preparation: role of substrate availability to modify training adaptation and performance. J Sports Sci 2007;25 Suppl 1: p. S115-24.

2. Symons TB, et al. A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects. J Am Diet Assoc 2009;109(9): p. 1582-6.

3. Moore DR, et al. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr 2009;89(1): p. 161-8.

4. Zhang XJ, Chinkes DL and Wolfe RR. Measurement of muscle protein fractional synthesis and breakdown rates from a pulse tracer injection. Am J Physiol Endocrinol Metab 2002;283(4): p. E753-64.

5. Walker DK, et al. Exercise, amino acids, and aging in the control of human muscle protein synthesis. Med Sci Sports Exerc 2011;43(12): p. 2249-58.

6. Guillet C, et al. Impaired anabolic response of muscle protein synthesis is associated with S6K1 dysregulation in elderly humans. Faseb J 2004;18(13): p. 1586-7.

7. Biolo G, Fleming Declan RY and Wolfe RR. Physiologic hyperinsulinemia stimulates protein synthesis and enhances transport of selected amino acids in human skeletal muscle. J Clin Invest 1995;95(2): p. 811-9.

8. Elango R, et al. Protein requirement of healthy school-age children determined by the indicator amino acid oxidation method. Am J Clin Nutr 2011;94(6): p. 1545-52.

9. Humayun MA, et al. Reevaluation of the protein requirement in young men with the indicator amino acid oxidation technique. Am J Clin Nutr 2007;86(4): p. 995-1002.

10. Reeds PJ and Garlick PJ. Protein and amino acid requirements and the composition of complementary foods. J Nutr 2003;133(9): p. 2953S-61S.

11. Walrand S, et al. Functional impact of high protein intake on healthy elderly people. Am J Physiol Endocrinol Metab 2008;295(4): p. E921-8.

12. Bouillanne O, et al. Impact of protein pulse feeding on lean mass in malnourished and at-risk hospitalized elderly patients: a randomized controlled trial. Clin Nutr 2012;32(2): p. 186-92.

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