Protein, often called the building block of life, comprises amino acids. The body uses amino acids to repair muscles, strengthen bones, and fuel daily activities. (1) While protein is vital for muscle growth and overall bodily functions, it’s a common belief that consuming too much can harm the kidneys.
However, new research challenges this assumption. Dr. Layne Norton addressed this topic in early December 2024. He delved into the findings of a recent study and offers insights into the relationship between protein intake and kidney health.
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Protein Consumption & Impact On Kidney Health
Dr. Norton reviewed a recent study exploring protein intake in older adults with either normal kidney function or chronic kidney disease (CKD). The study analyzed 14,399 observations from a sample of 8,543 participants.
Notably, researchers excluded about one-third of participants in the more advanced stages of CKD (stages four and five). (2) The risk of mortality for people with CKD decreased by 8% to 23% across intake ranges of 0.8 to 1.6 grams per kilogram of body weight. The risk decreased by almost 50% for people without CKD from 0.8 to 1.6 grams per kilogram of body weight.
Protein & Kidneys Bad Rep
The impact of protein on kidney health has been debated in medical literature for years. Individuals with kidney issues are generally advised to limit their protein intake to the bare minimum. Many doctors also recommend that patients adhere to a low-protein diet to manage their condition effectively.
“It comes from a bit of epidemiology mixed with some mechanistic speculation,” Norton stated, explaining that the amino acids in proteins contain a nitrogen component, specifically an amino group. However, this isn’t free ammonia, as free ammonia is highly toxic and potentially lethal. When bonded within an amino acid, it poses no harm.
When the body doesn’t use amino acids for protein synthesis, it repurposes them by oxidizing or utilizing their carbon skeletons for other functions. To achieve this, the body removes the amino group through deamination.
This triggers a sequence of metabolic reactions that ultimately convert the ammonia group into urea, a non-toxic compound safely excreted by the kidneys. “Because the kidneys are involved, some people have postulated that higher protein diets put more strain on the kidneys,” Norton explained.
More Research
Other studies demonstrate that protein intake doesn’t harm healthy kidneys. (3) Experts still recommend restricting protein intake if someone has kidney disease.
Norton says more studies have proven these recommendations might not be the best option. Some of these studies showed that not only does decreasing protein increase mortality, but increasing it consistently has a dose-dependent protective effect.
What About Animal & Plant Protein?
Reviewing the study, Dr. Norton noted that individuals with or without CKD who consumed more plant protein than animal protein experienced a more significant risk reduction. He attributes this to plants’ additional health benefits, such as fiber and essential minerals. While plant and animal proteins were found to have protective effects, plant proteins offered more substantial benefit.
The study revealed age-related differences in protein benefits. For participants under 75, plant and animal proteins provided advantages, peaking at approximately 1.2 grams per kilogram of body weight. In contrast, for individuals over 75, plant protein intake benefits increased linearly to 1.6 grams per kilogram.
[There isn’t] a strong argument that protein negatively affects a healthy kidney.
—Dr. Layne Norton
In conclusion, Dr. Norton advocates rethinking views of the relationship between protein consumption and kidney disease. This study suggests protein isn’t as harmful as commonly believed and may offer protective benefits.
“We have quite a bit of data to show that protein isn’t bad and might actually be protective. So we’ve been telling people to eat low protein if they have CKD for years; we might have actually been causing them more harm.”
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References
- Weijs, P. J., Cynober, L., DeLegge, M., Kreymann, G., Wernerman, J., & Wolfe, R. R. (2014). Proteins and amino acids are fundamental to optimal nutrition support in critically ill patients. Critical care (London, England), 18(6), 591. https://doi.org/10.1186/s13054-014-0591-0
- Carballo-Casla, A., Avesani, C. M., Beridze, G., Ortolá, R., García-Esquinas, E., Lopez-Garcia, E., Dai, L., Dunk, M. M., Stenvinkel, P., Lindholm, B., Carrero, J. J., Rodríguez-Artalejo, F., Vetrano, D. L., & Calderón-Larrañaga, A. (2024). Protein Intake and Mortality in Older Adults With Chronic Kidney Disease. JAMA network open, 7(8), e2426577. https://doi.org/10.1001/jamanetworkopen.2024.26577
- Devries, M. C., Sithamparapillai, A., Brimble, K. S., Banfield, L., Morton, R. W., & Phillips, S. M. (2018). Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets: A Systematic Review and Meta-Analysis. The Journal of nutrition, 148(11), 1760–1775. https://doi.org/10.1093/jn/nxy197
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