Many of us know that eating protein is a key component of a healthy, well-balanced diet. But understanding the specifics of how dietary protein actually regulates muscle protein metabolism, muscle mass, and muscle strength? Well—that might be a bit more of a question mark. (We feel you.)

The protein we consume (and produce) has a lot of different roles— importantly, the gains or losses of muscle mass depend on the balance of muscle protein we produce and breakdown. If you’ve ever been curious about protein’s specific role alongside your exercise, it might be useful to start with a crash course in something called muscle protein synthesis. Let’s break it down.

What Is Muscle Protein Synthesis?

“From a physiological standpoint, our muscle tissue is dynamic and in a constant state of turnover, with muscle proteins being synthesized and broken down simultaneously throughout the day,” says Harvard-trained physiologist, Professor Nima Alamdari, who is Chief Scientific Officer at Ritual and Honorary Professor of Sport and Health Sciences at the University of Exeter.

Basically, muscle protein synthesis is a metabolic process that produces muscle protein, facilitating the maintenance or building of muscle mass. It works in opposition to muscle protein breakdown that can accelerate the loss of muscle mass, as experienced in age-related muscle loss, immobilization, inactivity, and other catabolic (or breakdown) conditions. (1)

Loss of muscle mass and strength is of major public health concern, with age-related muscle loss being up to 2% of total muscle mass loss per year from the age of around 50 years onwards. But the good news is that our habits can have an impact, as the turnover of muscle protein is regulated largely by what you eat, and also how you move. (2)

Still with us? Let’s dive deeper.

“When muscle protein synthesis exceeds muscle protein breakdown, muscle hypertrophy [also known as muscle growth] occurs,” says Dr. Nima. “Muscle hypertrophy is dependent on the balance between muscle protein synthesis and breakdown and can be influenced by many factors, including nutrition and exercise.”

By now, it's probably pretty obvious that muscle protein synthesis is a pretty complex topic. But based on the latest research, there are things you can do to maximize muscle protein synthesis. Keep reading to learn more.

How to Optimize Muscle Protein Synthesis

1. Monitor your protein intake, quality, and timing.

Quality. Dietary protein provides amino acids needed for the synthesis of muscle protein, and that means emphasizing high-quality protein sources with complete amino acid profiles. (Quick crash course: Protein is made up of building blocks called amino acids, nine of which are considered “essential.” When a food or meal contains all nine essential amino acids at sufficient amounts, it’s considered “complete.”)*

Dietary protein-derived essential amino acids act as signals to induce muscle protein synthesis. Differences in protein types and sources result in differences in the magnitude of the muscle protein synthesis response, largely because of the differences in the availability of essential amino acids (and L-leucine in particular) to the muscle. This availability depends on different factors, including a protein’s essential amino acid composition and overall content. Suboptimal protein sources are associated with a lower essential amino acid content or shortage in a specific amino acid such as L-leucine, L-lysine, or L-methionine. All these amino acids are needed for protein synthesis and lack of one or more will compromise the protein synthesis response.* (1)

In other words, protein quality—and not just how much you're consuming—can be a pretty big factor here. That means considering the amino acid profile of the protein source in question. Certain animal protein sources provide a strong stimulus in muscle protein synthesis, and recently it’s been shown that certain plant-based proteins have a relatively high and balanced amino acid content. For example, soy protein has essential amino acid contents that meet the requirements as recommended by the World Health Organization/Food and Agriculture Organization of the United Nations/United Nations University (WHO/FAO/UNU), and pea protein comes really close (falling short on methionine). This information suggests certain plant proteins could be effective alternatives to animal proteins for a meaningful stimulation of muscle protein synthesis, especially if you consider pairing certain plant-based options together.* (3)

Intake. Again, quality is an important factor—but quantity also still plays a role. Studies have shown that around 20 g (or roughly 0.3 g/kg of body weight) of rapidly digested, high quality protein helps maximize the muscle protein synthesis response at rest, and after exercise. However, in older adults this amount may not be enough, with recent studies suggesting a heightened “anabolic resistance” as we age, and a need for further stimulating muscle protein synthesis.* (4,5)

While increased protein intake (30-40 g) for older individuals can help maximize muscle protein synthesis, other strategies may be more practical and easily adopted—and this is where quality (aka the amino acid profile) comes back into play. Specific amino acids have been shown to increase muscle protein synthesis and net balance, and supplementation with leucine, isoleucine, and valine has been used to support muscle maintenance. In particular, increased leucine consumption has been shown to increase the muscle protein synthesis rate in older individuals and may be of benefit to address normal age-related declines in muscle mass. There is also interest in β-hydroxy-β-methylbutyrate (HMB), a key metabolite of leucine, with demonstrated effects on protein synthesis and protein breakdown. Recent findings also suggest an age-related decline in endogenous HMB (aka the kind we produce ourselves) in the body. HMB supplementation has been tested in older adults, and there is a growing body of evidence that suggests HMB may help support muscle maintenance and measures of muscle strength.* (6)

Timing. When should protein your protein be consumed? Muscle protein synthesis is short lived and lasts around 4-5 hours. Therefore, consuming protein in regular intervals throughout the day is needed to help maximize net muscle protein accretion at rest, and timing protein consumption after exercise also further potentiates this effect.

2. Step up resistance training.

Although physical activity and exercise training of any type is excellent for overall health, aerobic exercise won’t do much for increasing muscle mass. Resistance exercise, however—that is, exercises that create mechanical tension and metabolic stress—certainly will. Muscle hypertrophy occurs when muscle protein synthesis is promoted over muscle protein breakdown. This can be achieved by targeted resistance training and sufficient protein intake which is why consideration should be given to both training type and diet. P.S. Exercise itself sensitizes the effects of protein to maximize muscle protein synthesis. This gives more reason to take protein within the first few hours after a workout, given the synergistic effect on muscle protein synthesis. * (7)

Another way of putting it? “It’s true that you need to move it or lose it," says Dr. Nima. "Resistance exercise combats the loss of muscle mass, which is particularly important for older adults.”

For increasing muscle mass through exercise, Dr. Nima says that “resistance training with a moderate number of reps (6−12), short rest intervals (60 seconds), multiple sets (3−6), and moderate loads (around 60−80% of your 1 rep max), with subsequent increases in training volume (12–28 sets per muscle, per week) generates greater metabolic stress which better stimulates muscle hypertrophy.” An important note: Maintaining proper form and technique throughout is essential. You don’t want to injure yourself in the process, which can be counterproductive in attempting to enhance muscle protein synthesis, and the maintenance or gain of lean muscle mass.

Resources:

1. Atherton, P. J., & Smith, K. (2012). Muscle protein synthesis in response to nutrition and exercise. The Journal of physiology, 590(5), 1049–1057.
2. Keller, K., & Engelhardt, M. (2014). Strength and muscle mass loss with aging process. Age and strength loss. Muscles, ligaments and tendons journal, 3(4), 346–350.
3. Gorissen, S., Crombag, J., Senden, J., Waterval, W., Bierau, J., Verdijk, L. B., & van Loon, L. (2018). Protein content and amino acid composition of commercially available plant-based protein isolates. Amino acids, 50(12), 1685–1695.
4. Schoenfeld, B.J., Aragon, A.A. How much protein can the body use… J Int Soc Sports Nutr 15, 10 (2018).
5. Burd NA, Gorissen SH, van Loon LJ. Anabolic resistance of muscle protein synthesis… Exerc Sport Sci Rev. 2013 Jul;41(3):169-73. doi: 10.1097/JES.0b013e318292f3d5. PMID: 23558692.
6. Rossi AP, D'Introno A, Rubele S, Caliari C, Gattazzo S, Zoico E, Mazzali G, Fantin F, Zamboni M. The Potential of β-Hydroxy-β-Methylbutyrate… Drugs Aging. 2017 Nov;34(11):833-840. doi: 10.1007/s40266-017-0496-0. PMID: 29086232.
7. Damas F, Phillips S, Vechin FC, Ugrinowitsch C. A review of resistance training-induced changes in… Sports Med. 2015 Jun;45(6):801-7. doi: 10.1007/s40279-015-0320-0. PMID: 25739559.