Protein For Endurance Athletes

Contributed by Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth, and Associate Professor of Exercise Physiology, Department of Human Sciences, and Department of Physiology and Cell Biology, The Ohio State University

A sensible, complete, whole food based nutrition plan for anyone, but especially athletes, must include appropriate quantities of each of the three macronutrients (protein, carbohydrate, and fat). Endurance athletes are no exception to this rule. Athletes need to fuel their training and provide their bodies the necessary nutrients to perform consistently, repair damaged tissue, and recover properly.

The macronutrient protein, and its dietary intake guidelines, seems to create unnecessary confusion for endurance athletes even through this area is widely studied by exercise physiologists. The bottom line for endurance athletes is that carbohydrates and fats are the two primary macronutrient fuels that are utilized for movement.

Protein is not in any way a significant source of fuel during exercise. Even in the presence of a diet high in protein this will not change, and it is widely accepted in the research literature that even when one is at rest that protein metabolism constitutes only 5% to 15% of your energy expenditure. Yes, during endurance exercise, in absolute terms, more amino acids may be metabolized for fuel. Relatively speaking though, protein as a fuel source during exercise is still not a major contributor due to the significantly greater increase in the utilization of carbohydrate and fat.

Accordingly, during prolonged endurance exercise the relative contribution of protein to energy expenditure is usually much lower than it is at rest, typically less that 5%. There have been research papers that report in extreme conditions, when carbohydrate availability is severely limited, protein utilization can elevate to as great as 10% of total fuel usage.

The recommended daily intake of protein for the average person is 0.8 grams of protein/kilogram of body weight. However, if you are an endurance athlete most scientists agree (and a significant amount of research supports) that a daily protein intake recommendation of 1.2 - 1.4 grams of protein/kilogram of body weight is best. The amount of recommended daily protein intake you require is easy to calculate. Simply divide your scale weight by 2.2 to go from pounds to kilograms. Then multiply that number by either 1.2 or 1.3 or 1.4 to arrive at the number of grams of dietary protein you should consume each day.

Recall that proteins are comprised of amino acids, and there are 20 proteinogenic (i.e., "protein building") amino acids. The 20 amino acid building blocks are used primarily to synthesize proteins in the body for various uses, including the repair and growth of skeletal muscle. Some amino acids are also utilized for the production of neurotransmitters and hormones.

Nine of the 20 amino acids are known as essential amino acids, because the human body is not able to produce them from other compounds. So the essential amino acids must be obtained from dietary foodstuffs or nutritional supplements. The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

The other are 11 amino acids are known as nonessential amino acids. Nonessential is a bit misleading in my opinion. These 11 amino acids actually are responsible for very important functions in your body, but since they can be synthesized (i.e., produced) by your body, they are not essential to obtain through your diet. Thus, the term nonessential. 

So your body can synthesize the 11 nonessential amino acids. However, there is one more very important twist that is important to understand. Of the 11 nonessential amino acids, eight of them are considered to be conditional amino acids. What conditional means is that when you are sick, fatigued, or under significant stress, your body may not be capable of producing enough of these 8 conditional amino acids to meet your metabolic needs. The eight conditional amino acids include arginine, glutamine, tyrosine, cysteine, glycine, proline, serene, and ornithine. The three remaining, alanine, asparagine, and aspartate are always nonessential, meaning your body is always able to produce them even under times of stress or fatigue.  

Finally, let me address the BCAA term, which stands for branch chain amino acids. This is a very popular and hot area in the supplement market right now, and has been for a few years. There are three branch chain amino acids - leucine, isoleucine, and valine, and all three of them are in the category of essential amino acids. The supplement market has latched on to BCAAs due primarily to a paper that was published in 2006. The data in this paper clearly indicated that the intake of leucine could increase muscle growth and repair and also potentially decrease appetite. This fact has resulted in an absolute explosion in the supplement market for BCAA products with some very exaggerated claims on the labels of the supplement packaging. 

My advice is to not focus on the intake individual amino acids. My advice is to consume between 1.2 – 1.4 grams of protein/kilogram of body weight every day. Focus on whole food, complete protein sources. Complete protein sources are those that contain all nine essential amino acids. Generally proteins from animal sources, including red meat, fish, poultry, and eggs are complete proteins. Vegetarian and vegan sources of complete proteins include soybeans and soy products (always choose non-GMO soy and soy products), pea protein, the grain quinoa, seaweed, and spirulina.