The first time I ever bought a protein supplement was as an entering high school freshman who had just made the varsity football team and wanted to put on some muscle. I remember the concerned look on my mother’s face as she brought a tub of MetRx to the counter and sincerely asked the worker if this was going to be harmful to my health in any way. He informed her it was equivalent to eating a chicken breast, so we bought the supplement. Since those days, good information has been spread and protein flavors have drastically improved. But there are still those that believe that eating “too much” protein can be hard on your kidneys and/or that the amounts that lifters and bodybuilders consume is excessive. Within this article we’ll explore both kidney health and quantity of protein intake to see if there is any merit to their concerns.
The recommended daily allowance (RDA) of protein for the average person is 0.8g/kg/day. It is common amongst bodybuilders and even recreational lifters to intake 2-4x that amount and has raised the question as to whether or not this is a safe amount. When looking at kidney health, samples of the urine and blood can be taken and analyzed to look for certain markers that would indicate unhealthy function. Some of these include glomerular filtration rate and albumin and calcium excretion rates. Poortmans and Dellalieux (2000) examined these indices among a group of bodybuilders and recreational lifters who were intaking near 2.0 g protein/kg bodyweight (BW). This being over double the RDA could possibly lead to hyperfiltration of the kidneys and obligatory oxidation of the liver (Poortmans & Dellalieux, 2000). But this wasn’t seen amongst either groups in this study. The researchers concluded that protein intake up to 2.8 g/kg BW was safe and showed no correlations between this level of intake and creatinine clearance, albumin excretion rate and calcium excretion rate (Poortmans & Dellalieux, 2000). One possible limitation to this study is that it was performed over a short period of time. The groups did a 7 day diet analysis but then performed their testing during a single session.
A study by Antonio et al., (2016) gathered a group of resistance trained males and analyzed the effects of their normal protein intake ~2.5 g/kg BW/day over a six month period. After this 6 month period they increased their protein intake to ~3.3g/kg BW/day and measured the effects after another 6 months. The researchers were unable to find any indication that the high protein intake, or the very high intake caused any negative effects to kidney or liver function (Antonio et al., 2016). Other interesting findings were that these participants did not see any harmful effects to blood lipids nor see increases to their fat mass, despite the increase in calories.
Although current research shows that protein intake that is much higher than the RDA is safe, that doesn’t necessarily imply that this amount is optimal or effective. In a different study, Antonio et al. (2016) looked to not only compare kidney and health measures of a high vs. very high protein intake but also performance. It was found that the group eating very high amounts of protein (~3.3g/kg BW) saw no significant increases to lean mass or bench press 1RM than the group eating high protein (~2.6g/kg BW). Schoenfeld et al. (2013) looked at the implications that total daily protein intake had on strength and hypertrophy outcomes. It was found that high protein had an effect on hypertrophy but not strength. Schoenfeld and Aragon (2018) argued that an optimal intake range may be between 1.6g/kg to 2.2 g/kg/day if the goal is to maximize muscle growth from resistance training for lifters who aren’t in a caloric deficit. They mention that intaking protein beyond these amounts won’t be harmful, may also not be additionally beneficial beyond what the suggested range provides. One instance that might justify higher intakes would be when bodybuilders are in a prolonged deficit, trying to get lean enough for competition. Helms et al. (2014) showed that in order for athletes to retain lean body mass during times of severe restriction intake levels may need to be as high as 2.3-3.1g/kg of fat free mass (not just bodyweight) per day! Beyond this scenario there may not be any need for such high intakes.
To understand why higher intake amounts aren’t always more beneficial to hypertrophy we can look at how our body reacts to ingested protein. There appears to be a “sweet spot” when it comes to stimulating muscle protein synthesis (MPS) between 0.4-0.55g/kg/meal over 4 meals (Schoenfeld & Aragon, 2018). When a participant was seen to ingest quantities beyond this amount it actually had a slight detrimental effect on MPS and lower amounts weren’t enough to stimulate MPS. This implies that there is not only an upper limit of effectiveness for our total daily protein intake and minimal amounts needed to fulfill our needs/goals, but also per meal. Research by Yasuda et al. (2020) reiterated this point, showing that evenly distributing protein intake over 3-4 meals augmented muscle hypertrophy. It’s explained that our bodies don’t really have a great storage mechanism for dietary protein. Whereas we store carbohydrates in our blood, liver and muscles and fat in our adipose tissue, we rely on ingested protein to fulfill our needs.
Current research has repeatedly shown that protein intake amounts as high as 3.2g/kg bw/day are not unhealthy to the kidneys, liver or other major health markers (Antonio et al., 2016). Although these amounts are not unhealthy, they can be excessive and perhaps wasteful given the cost of meat and/or supplemented protein. Current research suggest that an intake between 1.6-2.2g/kg bw/day is within an optimal range for those seeking to improve hypertrophy (Schoenfeld & Aragon, 2018). But, special consideration needs to be given to the distribution of this intake in order to further the optimization of protein consumption. Dividing the proper total daily intake evenly over 3-4 meals will ensure that MPS is maximally stimulated, excess intake isn’t wasted and that we aren’t undergoing prolonged periods of time without the protein that our body needs.
Antonio, J., Ellerbroek, A., Silver, T., Vargas, L., & Peacock, C. (2016). The effects of a high protein diet on indices of health and body composition - a crossover trial in resistance-trained men. Journal of the International Society of Sports Nutrition, 13, 1-7.
Antonio, J., Ellerbroek, A., Silver, T., Vargas, L., Tamayo, A., Buehn, R., & Peacock, C. A. (2016). A high protein diet has no harmful effects: A one-year crossover study in resistance-trained males. Journal of Nutrition & Metabolism, 1-5.
Helms, E. R., Zinn, C., Rowlands, D. S., & Brown, S. R. (2014). A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: A case for higher intakes. International Journal of Sport Nutrition and Exercise Metabolism, 24(2), 127-138.
Poortmans J. R., & Dellalieux, O. (2000). Do regular high protein diets have potential health risks on kidney function in athletes? International Journal of Sport Nutrition and Exercise Metabolism, 10(1), 28.
Schoenfeld, B. J., Aragon, A. A., & Krieger, J. W. (2013). The effect of protein timing on muscle strength and hypertrophy: A meta-analysis. Journal of the International Society of Sports Nutrition, 10(53).
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).
Yasuda, J., Tomita, T., Arimitsu, T., & Fujita, S. (2020). Evenly distributed protein intake over 3 meals augments resistance exercise-induced muscle hypertrophy in healthy young men. The Journal of Nutrition, 150(7), 1845-01851. https://doi.org/10.1093/jn/nxaa101