Protein Power

VA high-protein diet has become nearly synonymous with muscle building. Walk into any gym or grocery store and one is likely to find an entire section dedicated to protein shakes and supplements, not to mention the array of recipes and cookbooks focused on high-protein meals and snacks. But how much protein does the human body actually need to build muscle? And does the source of the protein matter?

Proteins are broken down into their constituent amino acids in the process of digestion. These amino acids are then absorbed through the walls of the small intestine, entering the portal venous system that directs them to the liver. After undergoing first-pass metabolism in the liver, the amino acids are made available to other tissues via the bloodstream (Schoenfeld and Aragon 2018). Muscle tissue serves as the primary storehouse of amino acids, and muscle anabolism and catabolism are highly dependent on the relative balance of protein in the body. Apart from their role in muscle building, amino acids are also used in the formation of hormones, enzymes, and various immunologic factors (Carbone and Pasiakos 2019). This is an oversimplification of the complex processes involved in protein metabolism, but it provides a basis for understanding the main focus of this article.

The recommended dietary allowance (RDA) of protein is around 0.8 grams per kilogram body weight per day. However, this number is based on the minimum amount of protein required to prevent a loss of muscle mass in a majority of the population (Carbone and Pasiakos 2019, Jäger et al. 2017). It does not, therefore, take into consideration the protein demands of those trying to gain muscle mass, nor does it meet the needs of active individuals trying to maintain muscle mass. The International Society of Sports Nutrition recommends, at a minimum, daily protein intakes of 1.4 to 2.0 grams per kilogram body weight for athletes and others undergoing resistance training, with higher intakes likely required for elderly individuals and those operating on an energy deficit to help maintain muscle mass (Carbone and Pasiakos 2019, Jäger et al. 2017).

Regarding the source of protein, the general consensus is that complete proteins—those containing all nine essential amino acids—are preferred over lower quality proteins or isolated amino acids. Examples of complete proteins include whey, meat, egg, and milk proteins. While technically a complete protein, soy contains limited amounts of several essential amino acids, which, among other factors, theoretically stymies its ability to promote muscle growth (Jäger et al. 2017). Interestingly though, several studies comparing whey, soy, and meat protein supplementation found no significant differences between supplement type and increases in muscle mass when combined with resistance training (Messina et al. 2018, Liao et al. 2024).

Another study from 2017 looked at the effectiveness of whey protein hydrolysate, whey protein concentrate, soy protein concentrate, and leucine supplements compared to placebo in promoting muscle gain when combined with resistance training over a 12-week period. This study also found no difference between any of the groups in muscle mass gains, although there was an increase in the number of satellite muscle cells in the whey protein groups (Mobley et al. 2017). Whether this finding translates into a future increase in muscle mass with prolonged exposure remains to be seen. This study highlights the question of supplementation with individual amino acids. While high-quality complete proteins are preferred, the branched chain amino acids (BCAAs), particularly leucine, do appear to exert independent and synergistic effects on muscle protein synthesis (Mobley et al. 2017, Jäger et al. 2017). Again, however, the consensus is that supplementation with BCAAs cannot and should not replace complete sources of protein, which already contain adequate amounts of these amino acids (Jäger et al. 2017).

Demand for supplemental sources of protein will likely grow in the coming years, especially as the world’s population continues to age. Manufacturers should prioritize fortifying their products with complete, high-quality proteins and expand their target audience to include elderly individuals, emphasizing the importance of protein in minimizing muscle loss.

Whey protein, in any of its various forms, contains all nine essential amino acids and has the greatest evidence supporting its efficacy in promoting muscle anabolism. However, for those who require or prefer an alternative source of protein, both soy and pea proteins appear to be effective (Liao et al. 2024, McKendry et al. 2024). Product formulators may further consider combining plant-based proteins to optimize their amino acid profiles (Berrazaga et al. 2019). Finally, while protein isolates and hydrolysates are generally more digestible than protein concentrates, this does not appear to have a significant impact on muscle protein synthesis and should thus remain a secondary consideration in product development (Koopman et al. 2009).

There is much more that could be said on this topic—from the role of carbohydrates to the timing and distribution of protein intake throughout the day. Suffice it to say that in combination with regular resistance training and adequate calories, a protein intake of 1.4 to 2.0 grams per kilogram of body weight is ideal for most adults aiming to increase their lean body mass.

When choosing protein supplements, complete proteins, such as whey or egg, are more effective than individual amino acids or BCAAs alone. Further research is needed to determine whether BCAAs stimulate greater muscle synthesis when added on top of already complete proteins.ft