What's the deal with high protein diets and protein supplements?
Diets containing above the Recommended Dietary Allowance (RDA) of protein have been shown to promote healthy aging, appetite regulation, weight management, and athletic performance (Phillips, Chevalier, and Leidy, 2016). High protein diets have also been a source of controversy for quite some time, and bodybuilders typically consume in the range of 2.2 to 4.4 g/kg of body weight (Helms, 2018). In a study following five well-trained bodybuilders over two years, Antonio and Ellerbroek (2018) observed an average intake ranging between 3.2 and 3.5 g/kg, with the highest intake in the study being 5.8g/kg. Kidney and liver function remained within normal levels over the course of the observational study, which included metabolic panels for liver and kidney function every six months (Antonio & Ellerbroek, 2018). This particular study is a continuation of a one year study of fourteen resistance-trained males by the same authors, which also found no negative effects related to a high protein diet (Antonio et al, 2016). The review by Phillips et al (2016) also reported a lack of evidence supporting the dangers of high protein diets on kidney, liver, and bone health.
It is important for athletes to consume high quality (high leucine content) proteins whenever possible, with animal proteins being the most beneficial (Smith-Ryan & Antonio, 2013; Phillips et al., 2016). Additionally, whey protein has the highest leucine content for optimized skeletal muscle protein synthesis (Smith Ryan & Antonio, 2013; Phillips et al., 2016). Within the whey protein family, hydrolysates are superior to concentrates and isolates (Smith-Ryan & Antonio, 2013). Hydrolysates increase the rate of muscle force recovery compared to non-hydrolyzed whey isolates, likely due to an increased rate of muscle glycogen replenishment (Smith-Ryan & Antonio, 2013). Additionally, hydrolyzed formulations aid in improved body composition due to decreased fat mass compared to isolates in resistance-trained individuals (Smith-Ryan & Antonio, 2013). This is likely due to changes in gut hormone release of gastric inhibitory peptide, which facilitates fat metabolism (Smith-Ryan & Antonio, 2013).
The original basis for cautions of the danger of high protein diets can be traced back to studies done in the 1920s on rats with one surgically removed kidney, which are hardly generalizable to otherwise healthy human individuals (Helms, 2018). It is worth noting, however, that some signals that are upregulated with high protein intake such as IGF-1 and insulin are also mechanistically useful for tumor growth, so further research is needed on the subject of high protein diets and cancer epidemiology (Helms, 2018).
Antonio, J., & Ellerbroek, A. (2018). Case Reports on Well-Trained Bodybuilders: Two Years on a High Protein Diet. Journal of Exercise Physiology Online, 21(1).
Antonio, J., Ellerbroek, A., Silver, T., Vargas, L., Tamayo, A., Buehn, R., & Peacock, C. A