You may have heard that protein is harmful for your kidneys. Generally, that’s not so. Unless your kidneys are damaged, eating high-quality protein is just fine.
Your kidneys, two bean-shaped organs just below the ribs that filter waste, naturally become less effective over time. A key measure of kidney function is the glomerular filtration rate (GFR). Glomerular refers to the glomerulus, a cluster of nerve endings and small blood vessels in the kidney that does the filtration work. GFR tends to decline with age. If your GFR is low for your age, you may be in trouble.
How does protein fit in? The body constantly adapts. Vegetarians tend to have lower GFRs than meat-eaters. When you take up a higher protein diet, your GFR may increase as much as 30 percent (Kramer, 2019).
Beginning in the 1980s, some researchers argued that a high-protein diet could overtax the kidneys since one of their main roles is to remove byproducts from protein digestion. They saw the higher GFRs linked to protein as a sign of stress that could lead to disease.
But others see it as a sign that the kidneys have become more functional. After all, GFR can rise safely. It rises in pregnant women by as much as 65 percent without any increase in disease (Devries et al., 2018). GFR also rises in the remaining kidney in kidney donors, and for as long as twenty years, without any increase in disease (Devries et al., 2018).
For all of us who appreciate the benefits of protein, it’s important to know that our kidneys are safe. It’s especially important if you’re past midlife and favoring protein to maintain your muscles. And it’s essential if you’re among the millions of Americans who are coping with obesity or diabetes via a higher-protein, lower-carbohydrate diet.
Remember that low - not high! - GFRs are a sign of possible kidney disease. In several large population-based studies, higher body mass index (BMI) is linked to low GFRs, with more rapid loss of GFR over time, and with kidney failure (Kovesdy et al., 2017). Diabetes is also a risk factor. In fact, about half of all U.S. kidney failure patients have diabetes. Another 29 percent have high blood pressure (National Kidney Foundation, 2020).
Getting leaner is, of course, a core remedy for metabolic disease - the dangerous combination of obesity, high blood pressure, and high blood sugar that can lead to type 2 diabetes and heart disease. You can fight back by eating more high-quality protein such as organic red meat and fish that is high in essential omega-3 fats. A protein-rich diet may make you feel fuller and avoid overeating. Combined with exercise, protein helps build or preserve lean muscle. That muscle will help you burn more calories in an ordinary day. Protein also helps promote fat loss (Bergia et al., 2019).
So will extra protein hurt your kidneys? The good news: When researchers at McMaster University in Ontario, Canada, analyzed data from 28 papers over more than 40 years, covering more than 1,300 participants in all, they found no evidence linking protein-rich diets to kidney trouble. This was true for all populations, including those with diabetes and other ailments that put them at higher risk for kidney disease (Devries et al., 2018).
Early signs, in fact, point to the idea that protein can help. In separate research with obese rats comparing the effects of a high vs. lower-protein diet for 12 weeks, the size of the kidneys increased in the high-protein group, but a blood indicator suggested the risk of kidney disease was lower (Devassy et al., 2017). A human study found that after a kidney transplant, higher protein intake decreased the death rate (Deetman et al., 2015).
When You Lack Extra Kidney Power.
The misunderstanding may have persisted in part because some of us can’t ramp up our kidney function as easily.
The working units of the kidneys are called nephrons, which include the glomeruli. You’ll typically have about 1.8 million nephrons, divided between your two kidneys. That’s many more than you need. Nephrons normally don’t work at full capacity. That’s why people can donate an entire kidney, half their nephrons.
But not everyone is blessed with abundant extra nephrons, and those people may be more vulnerable to kidney disease (Kramer, 2019). If you do develop a problem, evidence suggests it’s best to stick to low-to-moderate protein, since protein increases the demands (Kramer, 2019).
The wild card here is that kidney disease doesn’t have symptoms in the early stages. If you have diabetes or high blood pressure, take certain medications or have a family history of kidney disease, your doctor may recommend regular blood tests to check your kidney functions. If your GFR is low, your doctor will check your urine for high protein levels (proteinuria), a sign of chronic kidney disease.
Common over-the-counter drugs can increase your risk. Do you regularly take ibuprofen (Advil) or naproxen (Aleve)? Acetaminophen (Tylenol) may be safer for your kidneys.
If you need acid-reducers for heartburn, the proton pump inhibitors Nexium (esomeprazole), Prevacid (lansoprazole) and Prilosec (omeprazole) may raise your risk, and histamine-2 blockers such as Pepcid (famotidine) or Zantac (ranitidine) may be safer. Sugary drinks, alcohol, and smoking are linked to higher risk.
But until you know you have a problem, you needn’t worry that a low-carb diet with fish, eggs, and red meat will lead you to kidney dysfunction. Protein, especially if it is part of your strategy to stay lean and muscular, isn’t dangerous to healthy kidneys, and may actually help them function as they should during a long, healthy life.
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Bergia R, Wang Y, Hudson J, Campbell W. Protein Intakes Above the Recommended Dietary Allowance Reduce Fat Mass Irrespective of Energy Balance and Resistance Training Status: A Systematic Review and Meta-analysis (P08-056-19). OUP Academic. https://academic.oup.com/cdn/article/3/Supplement_1/nzz044.P08-056-19/5606479. Published October 24, 2019.
Deetman PE, Said MY, Kromhout D, et al. Urinary Urea Excretion and Long-term Outcome After Renal Transplantation. Transplantation. 2015;99(5):1009-1015 https://pubmed.ncbi.nlm.nih.gov/25393159/ Published May, 2015.
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Kidney Disease: The Basics. National Kidney Foundation. https://www.kidney.org/news/newsroom/factsheets/KidneyDiseaseBasics. Published May 15, 2020.
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Rughooputh MS, Zeng R, Yao Y. Protein Diet Restriction Slows Chronic Kidney Disease Progression in Non-Diabetic and in Type 1 Diabetic Patients, but Not in Type 2 Diabetic Patients: A Meta-Analysis of Randomized Controlled Trials Using Glomerular Filtration Rate as a Surrogate. PLoS One. 2015;10(12):e0145505. https://pubmed.ncbi.nlm.nih.gov/26710078/ Published Dec 28, 2015
Sithamparapillai A, Brimble KS, Banfield L, Morton RW, Phillips SM, Devries MC. 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. https://pubmed.ncbi.nlm.nih.gov/30383278/. Published November 2018. Accessed July 6, 2020.
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