If I had a dollar for how many times I have been asked “How much protein do you need every day?” I would retire tomorrow. It is probably the question I am asked the most in my day to day. It is a very important question, don’t get me wrong, but I believe it has come time to shift some of the focus of protein quantity to protein QUALITY.
When it comes down to it, what is the measure of protein quality? This is a tough question to answer because up until recently, the assumption was that all protein is created equal. I would argue that this is not the case. Like everything else in life, we have to establish the framework around this question. First, we need to establish the context for quality. For athletes, the quality of protein typically deals with how effective a protein source is at increasing muscle size, strength, power, and other training-induced adaptations. So to simplify the context, we are searching for how effective a protein is at stimulating Muscle Protein Synthesis (MPS).
As an athlete, MPS should be something you are both aware of and somewhat familiar with because “Muscle protein synthesis (MPS) is the driving force behind adaptive responses to exercise and represents a widely adopted proxy for gauging chronic efficacy of acute interventions, (i.e. exercise/nutrition).” Without MPS, there is no repair, growth, or positive athletic change.
Next, we have to figure out how much protein is needed to stimulate MPS. MPS is stimulated primarily in two ways. The first is through training. Let’s assume you are already doing that. The second is nutrient-dependent. What nutrients? All the macronutrients (Protein, Carbs, and Fats) play a role in MPS, but the nutrient that plays the most influential role is protein, and more specifically, the amino acids that make up protein. Of the 20 amino acids, 9 are considered Essential, and 11 are considered Non-Essential. The Essential Amino Acids (EAA’s) are given this characteristic because the body has to get them from the diet, whereas the Non-Essential Amino Acids (NEAA’s) can be “made” within the body through different processes. Ingesting NEAA’s does not stimulate MPS at all, while MPS is most effectively stimulated by the presence of EAA’s in your bloodstream.
So how much protein (or EAA’s) do you need to ingest in one sitting to maximally stimulate MPS? We are getting closer and closer to a definitive answer to this question. To figure this out, researchers have tested individual amino acids and groups of amino acids effects on MPS. Long story short, Leucine has the most potent effect on MPS, and these effects are most pronounced when the amount of Leucine ingested is at a threshold dose of around 2-3 grams. So now we can measure protein quality based on the Leucine content within a specific type of protein. Based on this criterion, whey protein is going to be one of the highest quality proteins because the Leucine content is around 11%. This means that you can maximally stimulate MPS with about 27 grams of whey. Other protein types have lower Leucine content, so in order to maximally stimulate MPS, you need to ingest more to reach the same Leucine threshold dose. Here are a few other protein types, their Leucine %, and how many grams of that protein to hit that 2-3 gram threshold dose.
- Milk, 9.8%: 31 grams
- Egg, 8.8%: 34 grams
- Fish, 8.1%: 37 grams
- Beef, 8%: 38 grams
- Chicken, 7.5%: 40 grams
- Wheat, 6.8%: 44 grams
Across the board, you’re looking at a minimum of 30 grams of protein to maximally stimulate MPS, though plant based protein sources have a much lower Leucine percentage, so much more of this type of protein has to be ingested to reach the threshold dose.
Related to MPS is what is known at the refractory period. The duration that MPS is increased due to Leucine concentrations elevated in the blood typically only lasts for 1.5-3 hours, even though the concentration of Leucine and other amino acids can remain elevated in the blood for longer than 3 hours. In order to maximally stimulate MPS again, the Leucine concentration in the blood has to drop below a set concentration, which occurs 4-6 hours after the protein/Leucine is first ingested.
Based on this data, the body may only be able to maximally stimulate MPS 4 or 5 times per day because of the refractory period needed to drop the Leucine concentration in the blood so it can then “spike” and re-stimulate MPS. It may actually not be beneficial to eat protein every 2-3 hours because if the Leucine concentration in your blood does not drop, the signal to stimulate MPS is not “reset” and you may only be stimulating MPS 1-2 times per day. Understanding this and spreading out your protein into 30-40+ gram meals every 4-6 hours may be the best way to get stronger, faster, and more powerful, but also recover, repair, and adapt to a greater extent.
So what is the takeaway? Well, I love bullet points, so here you go.
- Protein QUALITY is primarily dependent on the Leucine content
- Muscle Protein Synthesis is maximally stimulated at a dose of about 3 grams of Leucine
- Whey protein has the highest concentration of Leucine
- Due to the refractory period, shoot for a minimum of 30-40 grams of protein every 4-6 hours.
There you have it. Protein quality primarily comes down to Leucine content, and the total amount of protein you ingest needs to be seen through the lens of quality, not just quantity. Hitting your daily protein goal is important, but so it maximizing MPS.
About Kevin Kuhn:
Kevin Kuhn, M.S.Ed., CSCS, MFS is a Kinesiologist and Sport Nutrition Coach in Dallas, Texas. Before moving to Dallas in 2012, Kevin was the head strength & conditioning coach for the Indiana Invaders professional running club in Indianapolis, Indiana. Kevin specializes in athletic performance with great interest and experience in running-specific strength & conditioning, corrective exercise, and exercise and sport nutrition. Kevin has been certified by the National Strength & Conditioning Association as a Certified Strength and Conditioning Specialist (CSCS) and as a Master Fitness Specialist by the Cooper Institute.
References:
Atherton, P.J., Smith, K. (2012). Muscle protein synthesis in response to nutrition and exercise. J Physiol (Lond). 590(Pt 5):1049-57.
Houston, M. E. (2006.) Biochemistry primer for exercise science. Champaign Il: Human Kinetics.
Norton, L.E. (2010). Leucine is a critical factor determining protein quality and quality of a complete meal to initiate muscle protein synthesis (Doctoral dissertation). Retrieved from https://www.biolayne.com/wp-content/uploads/Layne-Norton-PhD-Thesis.pdf
Norton, L.E., Wilson, G.J., Layman, D.K., Moulton, C.J., Garlick, P.J. (2012) Leucine content of dietary proteins is a determinant of postprandial skeletal muscle protein synthesis in adult rats. Nutr Metab (Lond). 9(1): 67.
Norton, L.E., Wilson, G.J. (2009). Optimal protein intake to maximize muscle protein synthesis. Agro Food Ind Hi Tech. 20(2): 54-57.
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