It is commonly accepted that power and endurance athletes require, and therefore must consume, greater than the recommended daily intake of protein (Hoffman 2004). Protein supplements are used by athletes and physically active individuals to increase gains in strength and muscle mass and improve physical performance (Pasiakos 2015). These performance improvements include both anaerobic strength exercises and endurance activities. Along with increased muscle mass and improved performance, there are also claims that protein supplementation shows improved markers of recovery (Cintineo 2018).
Proteins are formed by amino acids and are the main structural component of muscle and other tissues in the body (Hoffman 2004). Supplementing protein can provide the essential amino acids that are used in muscle hypertrophy pathways. This can lead to increased muscle mass and strength gains that contribute to improved performance. Also, post-exercise protein consumption can maximize muscle protein synthesis, which may benefit recovery of muscle function (Cintineo 2018).
There is substantial evidence showing that consuming protein either before and/or immediately following a workout promotes a significant rise in muscle protein synthesis (Cintineo 2018). A systematic review by Pasiakos (2015) found that as resistance training volume, duration, and frequency increases, protein supplementation enhances gains in muscle mass and anaerobic and aerobic power. Another systematic review by Morton (2018) found that dietary protein supplementation during prolonged resistance exercise training enhances changes in muscle mass and strength such as increases in one-repetition maximum strength and fat free mass.
Regarding endurance outcomes, protein consumption during exercise does not provide immediate ergogenic benefit, but may assist with delaying central fatigue and reducing muscle protein breakdown. Furthermore, consuming protein post-workout optimizes the adaptive response to exercise training due to increased sensitization of muscle protein to nutrients 24-72 hours after training. (Cintineo 2018)
Protein supplements can be derived from various sources and the quality and composition may affect the nutritional benefit provided as well as the influence on physiological function. Protein quality is assessed based on essential amino acid composition, digestibility, and bioavailability of amino acids. Generally, sources of dietary protein are either of animal or plant origin, with animal sources considered a complete source of protein (containing all essential amino acids) and plant sources considered incomplete by lacking at least one of these essential amino acids. (Hoffman 2004)
Common types of animal protein supplements include whey and casein, while vegetable sources include pea, rice, and soy. Protein supplements can come in the form of concentrates or isolates, with protein content being 60-70% protein by weight and 90-95% protein by weight, respectively (Precision Nutrition 2017).
Limited research is available on comparisons of different protein sources and the effect on human performance. Different types protein have different digestibility and absorption rates making their use optimal during different times. Hoffman (2004) noted, "following whey protein ingestion, the plasma appearance of amino acids is fast, high and transient. In contrast, casein is absorbed more slowly producing a much less dramatic rise in plasma amino acid concentrations". Fast digesting proteins like whey and pea protein are utilized pre/intra-workout for quick absorption and ease of digestibility. Slow digesting proteins like casein and hemp are beneficial for recovery, especially overnight to provide steady absorption and minimize muscle catabolism. (Hoffman 2004)
The various protein sources allow for adequate intake for benefit while complying with dietary restrictions or preferences. Vegetable proteins can be combined to provide for all of the essential amino acids (Hoffman 2004). For example, pea and rice proteins are combined to create a complete plant-based protein that is similar in digestibility as whey, while being compatible with vegan or dairy sensitive diets.
The current Recommended Dietary Allowance (RDA) is 0.8g/kg/day of protein for healthy individuals, but evidence for optimizing training adaptations suggests a greater intake of at least 1.4-1.6g/kg/day (Cintineo 2018). Protein supplementation beyond 1.6g/kg/day during resistance exercise training provided no further benefit on gains in muscle mass or strength (Morton 2018).
Cintineo HP, Arent MA, Antonio J, Arent SM (2018). Effects of Protein Supplementation on Performance and Recovery in Resistance and Endurance Training. Frontiers in nutrition, 5, 83.
Hoffman JR, Falvo MJ (2004). Protein - Which is Best?. Journal of sports science & medicine, 3(3), 118-30.
Morton RW, Murphy KT, McKellar SR, et al (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Me. 52:376-384.
Pasiakos SM, McLellan TM, Lieberman HR (2015). The effects of protein supplements on muscle mass, strength, and aerobic and anaerobic power in healthy adults: A systematic review. Sports Medicine, 45(1), 111-131.
Precision Nutrition (2017). All About Protein Powders. Retrieved March 27, 2019, from https://www.precisionnutrition.com/all-about-protein-powders
Samal JRK, Samal IR (2018). Protein Supplements: Pros and Cons, Journal of Dietary Supplements, 15:3, 365-371