Background on Proteins

Proteins have many functions in the body, but many athletes and people think of protein only in the process of the make-up of tissues.  When building muscle it is commonly assumed that the more protein the more muscle, but there is more to proteins and their functions than just loading the body with protein.  Not all protein sources are created equal; some provide more protein per gram than others, some provide more complete forms of amino acid chains, some provide additional nutritional benefits, and some are more easily digestible than others.  Proteins are made up of a combination of different amino acids, of which 9 are essential, 11 non-essential, and then some can conditionally-essentially amino acids  “In general meat, poultry, eggs, and dairy products are complete protein sources, whereas plant products are incomplete protein sources” (McGuire & Beerman, 2013, p. 165).  That said combining two plant-based sources can complete the essential amino acid profile (Elkaim, 2014, p. 87).

It is important to keep in mind that just because it is a complete protein source doesn’t mean that it is easily absorbed; it also needs to be easily absorbed to be a high-quality protein source.  Another issue with proteins is the disruption of a protein’s shape, called denaturation.  Denaturation of a protein can result in poor absorption, loss of essential amino acids, loss of function and can even have serious chemical issues like acid/base and heavy metal reactions in the body (McGuire & Beerman, 2013, p. 173).   So many protein powders have high amounts of protein in them, but aren’t high quality, easily absorbed and can be denatured in the production process; which results in excretion or storage of proteins as body fat.

Protein turnover, the ability to break down and use protein, is what is important in protein utilization and is regulated mainly by hormones (McGuire & Beerman, 2013, p. 185).  Eating high glycemic carbohydrate diets, resulting in high insulin, inhibits protein utilization because the body is trying to utilize carbohydrates.  However, the release of cortisol during various types of stress, including exercise, stimulates protein use.  After exercise your body secretes cortisol and utilizes sugars directly into muscle, which is why you can utilize carbohydrates and protein at higher levels post-exercise.

Protein status in the end needs to be examined in nitrogen balance which is the amount of protein intake compared with the amount of nitrogen lost in the body (McGuire & Beerman, 2013, p. 187).  To prevent illness and muscle breakdown we need our body to have nitrogen balance which is when protein or nitrogen loss is equal to intake.  In order to build muscle or recover from illness or a workout we need our bodies intake to exceed loss and be in positive nitrogen balance.  Human bodies use protein for enzyme formation, movement, transportation and communication, immune system protection, fluid and electrolyte balance, and many other important functions in the human body; therefore the quality and quantity of proteins is important for health in general.  So how much protein does everyone need?


Athletes are causing more stress on the body from exercise than a non-athlete and need protein to rebuild muscle and prevent breakdown of the body seen with negative nitrogen balance.  The goal of sport and exercise needs to be determined in the amount of protein consumed.   Low and moderate-intensity endurance exercise does not affect dietary protein requirements, because low to moderate amounts of exercise are factored into the Recommended Dietary Allowances (RDA) of nutrients.  Athletes trying to put on muscle mass or endurance athletes that have strenuous training on the majority of days need a higher percentage of calories from protein.  There is some disagreement in recommendation levels of protein needed by athletes and (Philips, Moore, & Tang, 2007) did a review of different studies concluding that protein “timing and composition (quality) as well as consumption in combination with macronutrients such as carbohydrate; attention to these details, we contend, will enable athletes to perform to the best of their potential” (p. 71).  So it is important to keep in mind that even though there are recommended percentages and ranges for proteins within the athlete population, a number of factors need to go into recommended protein use.


In order to build muscle mass a person needs to be in positive nitrogen balance.  According to (Greenfield, 2014, p. 307) “there really isn’t much additional benefit to be gained by exceeding 0.55 grams per pound of body weight to maintain nitrogen balance.  That said when trying to exceed nitrogen balance and go into a state of positive nitrogen balance; studies suggest that you don’t need to go more than 25 percent above the .55 grams per pound of body weight, which ends up being .68 grams per pound of body weight (Wilson, 2006).  While being in a state of nitrogen balance it is important to remember that ammonia is a byproduct of the use protein and can be toxic to the body.  This means that having too much protein can result in toxic levels and can cause great strain on the body’s organs, in particular the kidneys.  Maintaining adequate water intake helps with the process of excreting the ammonia byproducts and therefore prevention of dehydration is very important in people with high protein intake (Greenfield, 2014, p. 308).  In summary, strength athletes need greater amounts of protein for a positive nitrogen balance, and is unnecessary to exceed 0.7 grams per pound of body weight on most days of the week because of the dangers ammonia can have on the body.


Aerobic and low to moderate endurance exercise is recommended and factored into the Institute of Medicine’s recommended macronutrient ratios.  Therefore, low and moderate-intensity endurance exercise does not affect dietary protein requirements in terms of the recommended macronutrient ratio of 10-20% of energy coming from proteins (Phillips, Moore & Tang, 2007, p. S59).  According to Mark Tarnopolsky (2004), the only time that endurance athletes need to exceed the recommended 12-15% of energy from protein intake is when an athlete is training 4 to 5 days a week for longer than 60 minutes; at that point Tarnopolsky recommends a diet of 20-25% of energy intake to be from protein (p. 666).  Another recommendation, outside of using percentages, to maintain nitrogen balance is 0.55 grams per pound of body weight for an athlete (Meredith, 1989).  That said, it is recommended and more common that endurance athletes train using cross-training techniques, including lifting and strength exercises which demand a higher percentage of energy intake from protein.  Protein recommendations for endurance athletes is slightly increased over the amount recommended for the average person if the athlete trains for greater than 60 minutes at least 4 to 5 day a week.


Weight Loss

Protein has been linked to weight loss and improved body composition, when combined with a reduction in total energy intake and/or combined with greater total energy used with exercise.  Research also suggests that protein is more satiating than ingestion of carbohydrate or fat, helping with reduced energy consumption due to an increased feeling of fullness.  Weight loss can be enhanced by minimally increasing protein intake, partaking in an energy-controlled diet, and maintained by making feasible, not radical, lifestyle adaptations  (Paddon-Jones, Westman, Mattes, Wolfe, Astrup, and Westerterp-Plantenga, 2008, p. 1561S).  Protein is a great tool to use with weight loss, but once again total energy in needs to be less than total energy used when losing weight.

Across the Lifespan

The US Recommended Dietary Allowance (RDA is 0.36 grams of protein per pound of body weight, which was designed for most people to be in nitrogen balance (Greenfield, 2014, p. 306-307).  As discussed in the athlete sections, this number doesn’t need to be excessively greater in strength and endurance athletes.  Across the lifespan, groups that need more protein per body weight include infants, breastfeeding women, and the aging population.  Infants need more protein per pound of bodyweight because of the rapid rate of growth.  Lactating women need more protein due to the fact that they are the primary nutritional source for themselves and their child.  Finally, the aging population needs additional protein because of the natural effects of muscle-mass loss, but kidney function also decreases with age.  Protein requirements are typically met by increasing the rates of protein from the previously recommended 10-20 percent of dietary percentage to 20-30 percent in the elderly in particular (Greenfield, 2013, p. 316).  In conclusion, a slight increase in protein intake as well as strength and weight-bearing exercise can help maintain appropriate muscle mass across the lifespan, while monitoring kidney function closely in the elderly.


Protein requirements aren’t as simple as just giving an exact amount for every athlete or every person in general.  It is important to understand your exercise or fitness goals, energy in still needs to equal to energy out if trying to maintain body mass and is adjusted per fitness goals.  Protein needs to be of high-quality because the protein can be denatured or not easily utilized for energy.  Understand that too much protein can cause added fat or strain on excretion process, including kidney failure, which is why for the average person only 10-20% of calories should be from protein.  In conclusion, it gets down to individualizing goals, understanding proper timing, and understanding an individual’s ability to synthesize and excrete nitrogen.     


Here is a bonus link to a website that looks into the bioavailability and quality of protein powder:

  • Don’t get all your protein from Protein Bars and Powders because even good sources don’t contain some of the nutritional benefits of “Real, Whole Foods”.  The 2010 Dietary Guidelines recommend getting “significant amounts of protein from at least 3 different food groups daily (McGuire & Beerman, 2013, p. 191)


Elkaim, Yuri. (2014). The all-day energy diet. Carlsbad, California: Hay House, Inc.

Greenfield, Ben. (2014). Beyond training: Mastering endurance, health, & life. Las Vegas: Victory Belt Publishing, Inc.

Meredith, C. (1989). Dietary protein requirements and body protein metabolism in endurance-trained men. Journal of Applied Physiology, 66(6), p. 2850-2856.

McGuire, M. & Beerman, K.A. (2013). Nutritional sciences: From fundamentals to food. Belmont, CA: Wadsworth.

Paddon-Jones, D., Westman, E., Mattes, R.D., Wolfe, R.R.,  Astrup, A., and Westerterp-Plantenga, M. (2008). Protein, weight management, and satiety. American Journal of Clinical Nutrition 87(5) p. 1558S-1561S.  Retrieved from

Phillips, S. M., Moore, D. R., & Tang, J. E. (2007). A critical examination of dietary protein requirements, benefits, and excesses in athletes. International Journal of Sport Nutrition and Exercise Metabolism 20(7), S58-S76. Retrieved from

Tarnopolsky, M. (2004). Protein requirements for endurance athletes. Journal of Nutrition (20)7, 662-668. doi:10.1016/j.nut.2004.04.008

Wilson, J. (2006). Contemporary issues in protein requirements and consumption for resistance trained athletes. Journal of International Social Sports Nutrition, 3(1), p. 7-27.