High-protein diets are often celebrated for their transformative effects on body composition and overall health. Yet, a shadow of concern hovers over these protein-rich regimens, particularly regarding their influence on kidney health. The central dilemma stirring up the nutrition community is whether these diets could potentially compromise our kidneys.
What is Protein?
The human body requires proteins for a myriad of functions[1]. They are indispensable for the construction and repair of body tissues, serving as the primary material for muscle growth, recovery, and maintenance. Beyond muscles, proteins are crucial for the health and integrity of hair, nails, and skin, contributing to their strength, elasticity, and resilience. This makes protein an essential nutrient not only for athletes and individuals engaged in regular physical activity but for everyone, as it supports the body's natural repair and growth processes.
There are twenty different amino acids that combine in various ways to create different proteins[2]. The human body can synthesize eleven of these, known as non-essential amino acids, on its own. However, the remaining nine amino acids, known as essential amino acids, cannot be made by the body and must be obtained through diet. This underscores the critical importance of consuming a varied and balanced diet, rich in protein sources to ensure the body receives all the essential amino acids it needs.
The importance of protein in the diet extends beyond its role in building and repairing tissues. Proteins also function as enzymes, facilitating countless chemical reactions within the body. They act as hormones, transmitting signals between cells, tissues, and organs. Proteins play a critical role in the immune system, helping to protect the body against pathogens. They are involved in the transportation and storage of molecules, and they provide structural support to cells and tissues.
Given the wide array of functions that proteins perform, it's clear that they are not merely a nutritional requirement for maintaining muscle mass and physical health but are fundamental to the body's overall functioning and well-being. Thus, ensuring adequate protein intake is essential for everyone, regardless of age, lifestyle, or level of physical activity, highlighting the importance of protein in our daily intake.
The Kidney-Protein Concept
Our kidneys serve as the body's natural filtration system, removing waste products like urea, which is generated from protein metabolism.
The process of protein metabolism and subsequent urea production is a normal and essential function of a healthy body. However, the hypothesis that has garnered attention within the medical and nutritional sciences communities posits that an increased intake of dietary protein could potentially overburden the kidneys. This concern stems from the fact that higher levels of protein in the diet lead to increased urea production. Consequently, the kidneys must work harder to filter and eliminate this surplus urea, along with other nitrogenous wastes.
Addressing Kidney Health Concerns
Current RDA recommendation for protein intake is 0.8 grams of protein/kg/day[3]. The notion that high-protein diets (diets with protein intake above the recommended 0.8 grams per day) could harm the kidneys is not without basis. Observational and animal studies have suggested a potential link between excessive protein consumption and kidney strain, particularly in individuals with pre-existing kidney issues. However, such studies often do not prove a direct cause-and-effect relationship, especially in healthy people.
Several long-term studies[4][5] have found that people with chronic kidney disease who eat a lot of protein might see their kidney function get worse over time. This includes findings from big research projects like the Nurses’ Health Study and the Gubbio Population Study. For example, in the Nurses’ Health Study, which followed women with mild kidney problems for 11 years, researchers found that for every extra 10 grams of protein these women ate daily, their kidney function dropped a little bit. This kind of drop in kidney function wasn't seen in people whose kidneys were working normally[5].
On the other hand, when examining the evidence from randomized controlled trials[4–12] with observation periods extending beyond six months, the data generally reveal minimal to no adverse effects of high-protein diets on kidney function in individuals with healthy renal systems.
What about research papers, such as meta-analyses, that summarize multiple randomized controlled trials?
Interestingly, a recent meta-analysis[13] incorporated 30 randomized controlled. It noted that there was no significant alteration in plasma creatinine levels in participants consuming a high protein diet. Plasma creatinine concentration is a commonly used marker to assess kidney function, with stable levels suggesting no detrimental impact on kidney health from dietary protein increases.
This body of research collectively suggests that for individuals without chronic kidney disease, consuming a diet high in protein does not appear to adversely affect kidney function.
Resistance Trained Individuals and High Protein Intake
A growing body of scientific evidence, including data from randomized-controlled trials, provides a counter-narrative for those with normal kidney function.
For example, a recent case-study[14] assessed 5 bodybuilders who were consuming a high protein diet (>2.2g/kg/day) over a course of 2 years. Subjects completed a comprehensive metabolic panel in a fasted state at a local Quest Diagnostics facility every 6 months. The findings showed no negative effects of high protein diet on liver or kidney functions.
Another study[15] looked at the effects of a high protein diet over one year period on 14 healthy resistance-trained men. In a randomized crossover design subjects consumed their normal diet for 2 months and then alternated with a higher protein diet for another 4 months (>3 g/kg/day). Following completion of the study, no harmful effects were found on measures of blood lipids as well as liver in kidney function.
Thus, the evidence from recent studies suggests that a high-protein diet does not negatively impact kidney or liver function in those with healthy renal systems.
Concluding Thoughts
- Observational studies suggest high-protein diets might worsen kidney function in individuals with chronic kidney disease.
- Randomized controlled trials indicate minimal to no adverse effects on kidney function from high-protein diets in healthy individuals, with some studies showing no change in key markers, like plasma creatinine.
- Case studies and research on resistance-trained individuals consuming high levels of protein for extended periods also found no detrimental effects on kidney or liver function.
- Overall, the consensus from recent scientific evidence suggests that while caution is advised for individuals with chronic kidney function, healthy individuals can safely consume high-protein diets without risking kidney damage.
References
1. Emery, P. W. (2015). Basic metabolism: protein. Basic Science, 33(4), 143-147. https://doi.org/10.1016/j.mpsur.2015.01.008
2. Fürst, P.; Stehle, P. What Are the Essential Elements Needed for the Determination of Amino Acid Requirements in Humans?1. J. Nutr., 2004, 134 (6), 1558S-1565S. https://doi.org/10.1093/jn/134.6.1558S.
3. Phillips, S. M. Dietary Protein Requirements and Adaptive Advantages in Athletes. Br. J. Nutr., 2012, 108 (S2), S158–S167. https://doi.org/10.1017/S0007114512002516.
4. Cirillo, M.; Lombardi, C.; Chiricone, D.; De Santo, N. G.; Zanchetti, A.; Bilancio, G. Protein Intake and Kidney Function in the Middle-Age Population: Contrast between Cross-Sectional and Longitudinal Data. Nephrol. Dial. Transplant., 2014, 29 (9), 1733–1740. https://doi.org/10.1093/ndt/gfu056.
5. Knight, E. L.; Stampfer, M. J.; Hankinson, S. E.; Spiegelman, D.; Curhan, G. C. The Impact of Protein Intake on Renal Function Decline in Women with Normal Renal Function or Mild Renal Insufficiency. Ann. Intern. Med., 2003, 138 (6), 460–467. https://doi.org/10.7326/0003-4819-138-6-200303180-00009.
6. Yancy, W. S., Jr; Westman, E. C.; McDuffie, J. R.; Grambow, S. C.; Jeffreys, A. S.; Bolton, J.; Chalecki, A.; Oddone, E. Z. A Randomized Trial of a Low-Carbohydrate Diet vs Orlistat Plus a Low-Fat Diet for Weight Loss. Arch. Intern. Med., 2010, 170 (2), 136–145. https://doi.org/10.1001/archinternmed.2009.492.
7. Comparison of the effects of 52 weeks weight loss with either a high-protein or high-carbohydrate diet on body composition and cardiometabolic risk factors in overweight and obese males | Nutrition & Diabetes https://www.nature.com/articles/nutd201211 (accessed Mar 11, 2024).
8. Effects of high‐protein diets on fat‐free mass and muscle protein synthesis following weight loss: a randomized controlled trial - Pasiakos - 2013 - The FASEB Journal - Wiley Online Library https://faseb.onlinelibrary.wiley.com/doi/pdfdirect/10.1096/fj.13-230227 (accessed Feb 21, 2024).
9. Flechtner-Mors, M.; Boehm, B. O.; Wittmann, R.; Thoma, U.; Ditschuneit, H. H. Enhanced Weight Loss with Protein-Enriched Meal Replacements in Subjects with the Metabolic Syndrome. Diabetes Metab. Res. Rev., 2010, 26 (5), 393–405. https://doi.org/10.1002/dmrr.1097.
10. Møller, G.; Rikardt Andersen, J.; Ritz, C.; P. Silvestre, M.; Navas-Carretero, S.; Jalo, E.; Christensen, P.; Simpson, E.; Taylor, M.; Martinez, J. A.; et al. Higher Protein Intake Is Not Associated with Decreased Kidney Function in Pre-Diabetic Older Adults Following a One-Year Intervention—A Preview Sub-Study. Nutrients, 2018, 10 (1), 54. https://doi.org/10.3390/nu10010054.
11. Krebs, J. D.; Elley, C. R.; Parry-Strong, A.; Lunt, H.; Drury, P. L.; Bell, D. A.; Robinson, E.; Moyes, S. A.; Mann, J. I. The Diabetes Excess Weight Loss (DEWL) Trial: A Randomised Controlled Trial of High-Protein versus High-Carbohydrate Diets over 2 Years in Type 2 Diabetes. Diabetologia, 2012, 55 (4), 905–914. https://doi.org/10.1007/s00125-012-2461-0.
12. Larsen, R. N.; Mann, N. J.; Maclean, E.; Shaw, J. E. The Effect of High-Protein, Low-Carbohydrate Diets in the Treatment of Type 2 Diabetes: A 12 Month Randomised Controlled Trial. Diabetologia, 2011, 54 (4), 731–740. https://doi.org/10.1007/s00125-010-2027-y.
13. Schwingshackl, L.; Hoffmann, G. Comparison of High vs. Normal/Low Protein Diets on Renal Function in Subjects without Chronic Kidney Disease: A Systematic Review and Meta-Analysis. PLOS ONE, 2014, 9 (5), e97656. https://doi.org/10.1371/journal.pone.0097656.
14. Antonio, J.; Ellerbroek, A. Case Reports on Well-Trained Bodybuilders: Two Years on a High Protein Diet.
15. Antonio, J.; Ellerbroek, A.; Silver, T.; Vargas, L.; Tamayo, A.; Buehn, R.; Peacock, C. A. A High Protein Diet Has No Harmful Effects: A One-Year Crossover Study in Resistance-Trained Males. J. Nutr. Metab., 2016, 2016, e9104792. https://doi.org/10.1155/2016/9104792.
