Protein Intake: Benefits, Myths, and Safety

Protein is well-known for its benefits in terms of body composition, strength, and reduced risk of injury. Strategies such as nutrient timing, dose, distribution, and type have been considered and studied to determine the optimal intake of protein regarding body composition and strength. High protein intakes have been questioned in terms of it being more beneficial regarding body composition goals or harmful regarding certain health markers such as renal and kidney function.

Body Composition and Muscle Mass

According to Jager et al. (2017), the optimal dose of protein per serving for athletes to stimulate muscle protein synthesis (MPS) depends on age and recent resistance-training stimuli. In general, if athletes prefer to distribute their protein intake throughout the day, .25g/kg is recommended or 20-40g/protein/meal. However, athletes should prioritize the total protein intake of 1.6g-2.2g/kg of body weight (Schoenfeld & Aragon, 2018). An optimal protein intake combined with resistance training incorporating progressive overloading is highly recommended to increase skeletal muscle mass and fat loss (Jager et al., 2017).

Injury Prevention

Nutritional strategies are well-known for their role in preventing injury and producing optimal recovery (Turnagöl et al., 2021). In particular, protein and amino acids have been shown to increase recovery by preventing muscle loss, therefore, reducing the risk of injury. Wall et al. (2015) suggested consuming protein to prevent muscle loss and anabolic resistance to protein during immobilization after injury. For athletes, it is recommended to consume 1.4g/kg/day during the injury period considering that increasing protein intake to 2.3g/kg/day showed a reduction in muscle loss while in a negative energy balance (Mettler et al., 2010; Petterson and Berg 2014). The amino acid content should also be considered, especially leucine as an essential role in protein synthesis. Baptista et al. (2010) found a delay in muscle loss in rats during immobilization after leucine supplementation. However, the benefits of leucine, in particular, regarding injury prevention merit more research, and athletes should focus on total protein aiming for moderate protein intake in each meal (Turnagöl et al., 2021).

Overall protein intake should be consumed from whole food sources such as grilled chicken, lean meats, eggs, and fish (Schoenfeld & Aragon, 2018). Supplementation with whey protein can benefit the athlete during times of low intake since whey is a “fast-acting” protein and can be digested at 10g/hr (Bilsborough & Mann, 2006).

Safety and Myths

Since high protein intakes seem to be popular, the safety of the high doses has been questioned especially considering the concerns of protein’s impact on health-related markers such as renal and kidney function.

According to some studies including Fouque et al. (2006), low protein diets showed positive outcomes in those who already struggled with chronic kidney disease. Randomized trials were selected that compared two different levels of protein intake. In conclusion, there was a 31% reduction in the occurrence of renal death in those with protein-restricted diets compared to those with high or unrestricted protein diets.

However, there is no current evidence that concludes the same outcome in healthy individuals with no kidney dysfunction. In a randomized crossover trial of healthy, resistant trained men, Antonio et al. (2016) found that high protein intakes didn’t lead to any significant changes in body composition nor were there any side effects present such as renal, kidney function, blood lipids, glucose and more. The 12 subjects who increased their intake consumed 2.6 to 3.3 g/kg/day for four months and did not show any sign of renal or hepatic dysfunction. Antonio et al. (2014) found no adverse outcomes as a result of a high protein diet (4.4g/kg) in another study of healthy resistance-trained men and women.

The authors of Stronger by Science have also broken down studies that claim a protein-rich diet can negatively impact kidney function and discuss their limitations in their podcast.

References:

Antonio, J., Peacock, C. A., Ellerbroek, A., Fromhoff, B., & Silver, T. (2014). The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals. Journal of the International Society of Sports Nutrition, 11, 19. https://doi.org/10.1186/1550-2783-11-19

Baptista, I. L., Leal, M. L., Artioli, G. G., Aoki, M. S., Fiamoncini, J., Turri, A. O., Curi, R., Miyabara, E. H., & Moriscot, A. S. (2010). Leucine attenuates skeletal muscle wasting via inhibition of ubiquitin ligases. Muscle & nerve, 41(6), 800–808. https://doi.org/10.1002/mus.21578

Bilsborough, S., & Mann, N. (2006). A review of issues of dietary protein intake in humans. International journal of sport nutrition and exercise metabolism, 16(2), 129–152. https://doi.org/10.1123/ijsnem.16.2.129

Fouque, D., Laville, M., & Boissel, J. P. (2006). Low protein diets for chronic kidney disease in non diabetic adults. The Cochrane database of systematic reviews, (2), CD001892. https://doi.org/10.1002/14651858.CD001892.pub2

Hoffman, J. R., Ratamess, N. A., Kang, J., Falvo, M. J., & Faigenbaum, A. D. (2007). Effects of protein supplementation on muscular performance and resting hormonal changes in college football players. Journal of sports science & medicine, 6(1), 85–92.

Jäger, R., Kerksick, C. M., Campbell, B. I., Cribb, P. J., Wells, S. D., Skwiat, T. M., Purpura, M., Ziegenfuss, T. N., Ferrando, A. A., Arent, S. M., Smith-Ryan, A. E., Stout, J. R., Arciero, P. J., Ormsbee, M. J., Taylor, L. W., Wilborn, C. D., Kalman, D. S., Kreider, R. B., Willoughby, D. S., Hoffman, J. R., … Antonio, J. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14, 20. https://doi.org/10.1186/s12970-017-0177-8

Mettler, S., Mitchell, N., & Tipton, K. D. (2010). Increased protein intake reduces lean body mass loss during weight loss in athletes. Medicine and science in sports and exercise, 42(2), 326–337. https://doi.org/10.1249/MSS.0b013e3181b2ef8e

Pettersson, S., & Berg, C. M. (2014). Dietary intake at competition in elite Olympic combat sports. International journal of sport nutrition and exercise metabolism, 24(1), 98–109. https://doi.org/10.1123/ijsnem.2013-0041

Schoenfeld, B. J., & Aragon, A. A. (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 15, 10. https://doi.org/10.1186/s12970 0180215-1

Turnagöl, H. H., Koşar, Ş. N., Güzel, Y., Aktitiz, S., & Atakan, M. M. (2021). Nutritional Considerations for Injury Prevention and Recovery in Combat Sports. Nutrients, 14(1), 53. https://doi.org/10.3390/nu14010053

Wall, B. T., Morton, J. P., & van Loon, L. J. (2015). Strategies to maintain skeletal muscle mass in the injured athlete: nutritional considerations and exercise mimetics. European journal of sport science, 15(1), 53–62. https://doi.org/10.1080/17461391.2014.936326