Nutrition Tips

Protein Quality

Posted on January 28, 2025

What is Protein Quality (and why are sports dietitians always discussing it!)?

The term "protein" was coined in 1838 by Gerrit Jan Mulder, a Netherlands physician and chemist (1). Since its discovery, protein has been one of the most hotly debated topics in nutrition. Nutrition scientists have worked tirelessly to determine protein's appropriate proportions and quality within the diet to optimize human health. Regardless of age or activity level, athletes and exercising individuals should maximize the opportunity to include high-quality protein sources in adequate amounts throughout all meals to help achieve their performance goals and a healthy eating pattern (2).

What Is Protein (combinations of amino acids)

Protein type is defined by the amino acid building blocks, which determine its characteristics and role within bodily functions (3). Dietary protein is broken down into its amino acid components during digestion. The body utilizes these amino acids to support the growth, transport, and storage of nutrients, tissue repair and the removal of waste deposits. Protein within the body is critical in adequately functioning the muscles, bones, skin, hormones and immune system (4). In addition, in times of need, amino acids can also become a critical energy source for the body (3).

How Much Protein Do We Need?

The recommended dietary allowance (RDA) for protein is 0.8g/kg for healthy adults (5). This level was initially determined as the minimum daily intake required to maintain nitrogen balance, defined as enough high-quality protein to prevent the catabolism of the body's protein stores. However, preventing bodily protein breakdown is not the same as optimizing function within the body, especially considering the variability of individual factors such as growth, exercise habits, ageing, hospitalization or disease. The most recent International Society of Sports Nutrition position stand suggests that exercising individuals aim for protein quantity intakes of 1.4-1.2g/kg spread throughout the day within two to three meals per day, each containing ≈ 25-30g/meal may confer more benefits for both the stimulation of 24-hr muscle protein synthesis and other metabolic benefits including improved body composition and enhanced satiety (6,7,8,9,10). This amount in kg translates to 0.63 to 0.9 grams of protein per day per pound of body weight.

What Are the Essential Amino Acids (EAA) So Essential?

Experts agree that a variety of high-quality protein foods with diverse amino acids should be included in the diet to support muscle maintenance, growth and dietary quality (11). There are nine essential amino acids that cannot be created internally and, therefore, must be obtained via nutritional sources (3). These are threonine, tryptophan, methionine, leucine, isoleucine, lysine, phenylalanine, valine and histidine. Plant and animal proteins differ in that plant proteins often do not contain sufficient quantities of EAAs and, therefore, are termed "incomplete" sources of protein when consumed as a single isolated source. Animal-based protein sources contain all nine essential amino acids and are more bioavailable than plant protein sources (3). Therefore, the quality of protein sources, precisely the amounts of EAAs provided by the protein source, impacts the amount of protein synthesis that can occur. Athletes must consume essential amino acids in sufficient quantities due to the continual breakdown and rebuilding of muscles engaged in resistance and aerobic training for sports. Regarding stimulating muscle protein synthesis after workouts, animal protein (compete for sources) confers an advantage over plant proteins when matched in the exact quantities (you can meet the same digestibility and EAA content, but it will take more plant protein quantity to do so).

Combining Protein Sources to Make Higher-Quality Protein

The term "complementary proteins" was coined in the 1970s to identify the necessity of combining two incomplete sources of plant proteins to create a source that supplied all nine essential amino acids within the same meal (12). However, research has suggested that if a variety of amino acids are consumed throughout the day, the essential amino acids stored within the liver can ensure adequate nitrogen retention and use in healthy adults (13). While combining two complementary proteins within the same meal is unnecessary, highlighting these pairings may help those aware of these complementary sources know they meet their needs with plant-based sources on menus or meal plans. Food pairs that will provide all the essential amino acids within the same meal or on the same day are legumes with grains, nuts, seeds or dairy, grains with dairy, and dairy with nuts or nuts or seeds and legumes.

Ready to Calculate Your Daily Protein Needs (for adults)?

  1. Start by determining your current weight in pounds
  2. Based on your age, fitness level, and individual goals (gain muscle, maintain muscle while recovering from surgery, etc.), use the table below to place yourself into the appropriate category
  3. Multiply your weight by the appropriate multiplier range to determine both the low and the high end of grams of protein you need daily.

Multiplier to Determine Grams of Protein Needed Per Day

Sedentary or Minimal Activity adults (Workouts 2-3 times per week for 20-30 mins. Per session)

0.54-.73

1 hour of moderate to vigorous activity 5 days per week (5-6 hours of activity per week total)

0.63-0.82

1 to 2 hours of moderate to vigorous activity per week (approximately 10 to 12 hours per week total). This also includes 4-5 days of resistance training athletes of approximately 1-2 hours per session.

.73-.9

If athlete goals include muscle weight gain, particularly during times of slight calorie restriction

0.9-1.12

Injured athletes looking to maintain muscle mass during periods of recovery or those recovering from surgery

0.9-1.13

By using the above table, athletes can start to understand a general gauge of their protein needs, combined with an increased focus on protein quality, to achieve their performance, body composition, and recovery goals.

References:

  1. Brouwer, E. & Mulder, G.J. (1952). Protein. Journal of Nutrition, 46, 3-11.
  2. Burd, N. A., McKenna, C. F., Salvador, A. F., Paulussen, K., & Moore, D. R. (2019). Dietary Protein Quantity, Quality, and Exercise Are Key to Healthy Living: A Muscle-Centric Perspective Across the Lifespan. Frontiers in nutrition, 6, 83. doi:10.3389/fnut.2019.00083
  4. Wu, G. (2013). Functional amino acids in nutrition and health. Amino Acids, 45(3), 407-411. doi:10.1007/s00726-013-1500-6
  1. Rodriguez, N. R. (2015). Introduction to Protein Summit 2.0: continued exploration of the impact of high-quality protein on optimal health. The American Journal of Clinical Nutrition, 101(6). doi: 10.3945/ajcn.114.083980
  3. Institute of Medicine Food and Nutrition Board. Dietary Reference Intakes: Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: National Academies Press; 2002.
  5. Layman, D. K., Anthony, T. G., Rasmussen, B. B., Adams, S. H., Lynch, C. J., Brinkworth, G. D., & Davis, T. A. (2015). Defining meal requirements for protein to optimize metabolic roles of amino acids. The American Journal of Clinical Nutrition, 101(6). doi: 10.3945/ajcn.114.084053
  7. Jäger, R. et al. (2017) ‘International Society of Sports Nutrition Position Stand: Protein and exercise’, Journal of the International Society of Sports Nutrition, 14(1). doi:10.1186/s12970-017-0177-8.
  9. Lonnie, M., Hooker, E., Brunstrom, J. M., Corfe, B. M., Green, M. A., Watson, A. W., … Johnstone, A. M. (2018). Protein for Life: Review of Optimal Protein Intake, Sustainable Dietary Sources and the Effect on Appetite in Ageing Adults. Nutrients, 10(3), 360. doi:10.3390/nu10030360
  1. Loenneke, J. P., Loprinzi, P. D., Murphy, C. H., & Phillips, S. M. (2016). Per meal dose and frequency of protein consumption is associated with lean mass and muscle performance. Clinical Nutrition, 35(6), 1506–1511. doi: 10.1016/j.clnu.2016.04.002
  3. Symons, T. B., Sheffield-Moore, M., Wolfe, R. R., & Paddon-Jones, D. (2009). A Moderate Serving of High-Quality Protein Maximally Stimulates Skeletal Muscle Protein Synthesis in Young and Elderly Subjects. Journal of the American Dietetic Association, 109(9), 1582–1586. doi: 10.1016/j.jada.2009.06.369
  5. Phillips, S. M., Fulgoni, V. L., Heaney, R. P., Nicklas, T. A., Slavin, J. L., & Weaver, C. M. (2015). Commonly consumed protein foods contribute to nutrient intake, diet quality, and nutrient adequacy. The American Journal of Clinical Nutrition, 101(6). doi: 10.3945/ajcn.114.084079
  7. Palmer, S. (2017, February). Plant Proteins - Today's Dietitian Magazine. Available at: from https://www.todaysdietitian.com/newarchives/0217p26.shtml. Accessed October 25, 2019
  10. Melina, V., Craig, W., & Levin, S. (2016). Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. Journal of the Academy of Nutrition and Dietetics, 116(12), 1970–1980. doi: 10.1016/j.jand.2016.09.025