Plant-Based Protein, Protein Quality, & Performance

An athlete’s diet is extremely important to performance. Plant-based diets have experienced a surge in popularity lately, but is a vegan lifestyle compatible with a high-performance environment? In a world full of divisive opinions, cherry-picked research, and anecdotal evidence it can be difficult to ascertain what is real and what is not. The truth is constructing a vegan diet that can support the demands of performance training can be challenging and an athlete should take time to consider if the time and effort to employ such a diet is worth it.

Plant-based diets can be inconvenient and somewhat difficult in dealing with nutritional deficiencies. This is a reality a vegan athlete must accept if they wish to make the diet successful. Nutrients such as healthy fats and cholesterol, B12, zinc, carnitine, and choline need to be found through carefully selected foods and supplementation. The lack of protein in a plant-based diet is often cited as its biggest issue, but this is one criticism that isn’t entirely true. The difficulty isn’t in quantity alone, but rather the quantity of quality protein.

The comparison between the quality animal protein and plant protein is no contest. Animal proteins contain all nine EAA (essential amino acids), are easily absorbed by the body, and have concentrations of amino acids that support soft tissue grown and recovery. The amino acids leucine, isoleucine, and valine, known together as the branched chain amino acids (BCAAs) are particularly useful in stimulating muscle anabolism and are great importance to anyone who puts a great demand on their body.

To say BCAAs are anabolic is really saying BCAAs stimulate mTOR. Mammalian target of rapamycin (mTOR) is a central protein in the signaling pathway of muscle protein synthesis (MPS) that plays a major role in cell growth and metabolism. It is stimulated by both diet and exercise, but amino acid/protein supplementation has been shown to stimulate mTOR to a greater extent than exercise alone. BCAAs, especially leucine, have been shown to stimulate the mTOR pathway independent of other EAAs.

Athletes clearly need to consume protein that has a high bioavailability and amino acid profile that will support anabolism, but it is at these measures where plant-based proteins have their short-comings. Apart from soy, quinoa, and buckwheat plant proteins are incomplete and require the combination of a variety of foods to complete an amino acid profile. They lack the necessary concentration of EAAs (approx. 85% less when compared to animal) and especially BCAAs to generate significant MPS. This becomes especially problematic when you consider the rate limiting quality of amino acids. Protein synthesis can only occur at the rate which the lowest concentrated essential amino acid is available. If the supply of one EAA is exhausted, none of the other can be used, which causes serious limitations to muscle protein synthesis (MPS).

“If a diet is inadequate in any essential amino acid, protein synthesis cannot proceed beyond the rate at which that amino acid is available. This is called a limiting amino acid. Because the depletion of just one of the essential amino acids prevents protein synthesis the process illustrates the all or none principle. Either all nine essential amino acids are available or none can be used. The essential amino acids in smallest supply in food or diet in relation to the body’s needs become the limiting factor (called the limiting amino acid) because it limits the amount of protein the body can synthesize”. -Perspectives in Nutrition; 6th Edition

Soy, being a complete protein with a decent concentration of leucine, is a potentially plausible choice for athletes. Unfortunately, it contains phytoestrogens that have been shown to increase an enzyme called AMP-activated protein kinase (AMPK), which regulates cellular energy and is activated in muscles by means of glucose deprivation and exercise. Activated AMPK enhances processes that generate ATP, like glucose transport and fatty acid oxidation, but also decreases muscle protein synthesis as elevating AMPK will coincide with a drop in mTOR. This is great for mobilizing fatty acids, not so great for anabolism. Contrarily, whey protein has been popular among active populations for so long because of its high concentration of leucine and low-fat content making it a fantastic means of glycogen replenishment and MPS. It is far superior to soy and even a better choice post-workout than meat and egg proteins.

Nutrition is a personal choice. There are many admirable reasons why people would choose a plant-based diet, but empirical evidence shows these diets may not be the most practical choice for athletes. Fruits, vegetables, nuts, and seeds offer many nutrients and should be included in every diet but fall short when it comes to muscle development and performance recovery. The only conceivable way for a vegan diet to work comes with a painful amount of nutritional juggling, supplementation, and possibly anabolics. Over-complicating something that should be intuitive, like nutrition, seems to go against our better judgement.

Sources

D. Joe Millward (1999). The nutritional value of plant-based diets in relation to human amino acid and protein requirements. Proceedings of the Nutrition Society, 58, pp 249-260. doi:10.1017/S0029665199000348.

Wilson, J., & Wilson, G. J. (2006). Contemporary Issues in Protein Requirements and Consumption for Resistance Trained Athletes. Journal of the International Society of Sports Nutrition, 3(1), 7–27. http://doi.org/10.1186/1550-2783-3-1-7

Hartman J., Tang j. (2007). Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters. The American Journal of Clinical Nutrition, 86 (2), 373-381. http://ajcn.nutrition.org/content/86/2/373.full

Blomstrand E., Eliasson J. (2006) Branched-Chain Amino Acids: Metabolism, Physiological Function, and Application: Session. The Journal of Nutrition, 136, 269S – 273S. http://jn.nutrition.org/content/136/1/269S.long

Cederroth C., Vinciguerra, M., (2008). Dietary Phytoestrogens Activate AMP-Activated Protein Kinase With Improvement in Lipid and Glucose Metabolism. Diabetes, 57 (5), 1176-1185

Wardlaw G., Hampl J., Disilvestro R. (2003) Perspectives In Nutrition 6th Edition. New York, NY: McGraw-Hill

Smith-Ryan A., Antonio, J. (2013) Sports Nutrition & Performance Enhancing Supplements. Ronkonkoma, NY; Linus Learning

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