Protein is a vital macronutrient for building, repairing, and maintaining muscle mass. Research suggests healthy individuals consume between 0.8 to 1.6 grams of protein per kilogram of body weight. (1)
However, the debate continues about the impact of high protein consumption, particularly regarding kidney and renal health, as highlighted in the study above. This raises the question: what amount of protein is excessive for kidney health, if any?
Dr. Layne Norton recently explored this topic with an in-depth analysis on Nov. 6, 2024, examining studies on the relationship between protein intake and kidney impairment.
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High-Protein Diets
Dr. Norton discussed the long-standing belief that high protein intake harms the kidneys. This notion dates back decades and stems from the understanding that proteins are composed of amino acids, which contain an ammonia component that must be converted to urea and eliminated through the kidneys.
Consequently, it was thought this process might stress the kidneys, leading to the recommendation that individuals with kidney issues reduce their protein consumption. This advice evolved into the belief that limiting protein intake could help prevent kidney disease.
According to Dr. Norton, this idea gained traction over time, supported by some correlational data. However, he highlights recent findings from a meta-analysis of human randomized controlled trials that indicate high-protein diets don’t increase the risk of kidney disease. (2) Critics argue that these trials were too short to capture the long-term development of chronic kidney disease (CKD).
In response, Dr. Norton refers to a new meta-analysis that explores the relationship between dietary protein intake and the incidence of CKD, distinguishing between animal and plant protein sources. (3) This recent meta-analysis:
- Excluded studies that reported protein intake and its effect on the progression of kidney disease. It looked at protein intake in healthy kidneys and the incidence of kidney disease.
- Factored in the age of participants.
- Excluded retrospective studies.
- Dismissed studies that didn’t report actual outcome data of kidney disease.
Following all exclusions, the meta-analysis comprised 150,000 participants, with most studies presenting a low risk of bias and high-quality evidence. A sensitivity analysis was conducted, removing each study individually to assess its impact on the results. Norton noted that the average length of these studies ranged from six to 23 years, with the majority being between 10 and 15 years long.
The Effects
The meta-analysis arrived at the following results:
- Higher total protein reduced the relative risk of kidney disease incidents by 16%.
- Those who had high total protein for animal protein reduced the risk of kidney disease incidents by 14%. However, the primary protein source for most of the studies was fish protein.
- Plant protein was associated with a 20% reduced risk of kidney disease incidents.
Critique
Dr. Norton’s major challenge with the cohort studies is that they didn’t harmonize what they considered high and low proteins. “I went to some of the studies cited, and some studies defined low protein as less than 13% of total energy and high protein as over 16% of total energy,” Norton explained. “But pretty consistently, higher protein intakes were associated with a lower risk of kidney disease.”
Those with higher protein intake may be healthier overall due to more active lifestyles, contributing to the results. However, this meta-analysis indicates a high protein intake is not inherently harmful to kidney function.
Moreover, Dr. Norton believes reverse causality doesn’t apply to the results since no connection between the kidneys and the brain would prompt individuals with healthy kidneys to consume more protein-rich foods.
“As of now, at least moderately high protein intakes do not appear to be detrimental to kidney function or the incidence of kidney disease,” Dr. Layne Norton reiterates.
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References
- Wu G. (2016). Dietary protein intake and human health. Food & function, 7(3), 1251–1265. https://doi.org/10.1039/c5fo01530h
- 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
- 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
Featured image via Shutterstock/F01 PHOTO
