Kidneys and High-Protein Diets: What the Science Says

Few nutrition debates are as persistent as the idea that eating lots of protein "wrecks your kidneys." Athletes and people following high-protein weight-loss diets hear it constantly. The reality depends heavily on whether the kidneys are already healthy. Our editorial team reviewed the physiology and the research.

How the kidneys handle protein

When you eat protein, it is broken down into amino acids. Those not used for building tissue are deaminated, mainly in the liver, producing ammonia, which is converted into urea. The kidneys then filter urea from the blood and excrete it in urine.

The kidneys filter blood through about a million tiny units in each kidney called nephrons. The overall filtering rate is called glomerular filtration rate (GFR). A protein-rich meal temporarily increases GFR, a normal phenomenon known as hyperfiltration.

The concern behind the myth is that chronic hyperfiltration might wear out the kidneys over time. This idea emerged largely from studies in animals and people with existing kidney damage.

In healthy kidneys, however, this increase in filtration appears to be an adaptive response, similar to how the heart increases output during exercise.

Research in healthy people

Randomized trials and meta-analyses in healthy adults have generally found no harmful effect of high-protein diets on kidney function. A 2018 meta-analysis by Devries and colleagues concluded that higher protein intakes did not adversely affect kidney function in people without kidney disease.

Studies in resistance-trained men consuming very high protein intakes, sometimes above 2.5–3 g/kg per day, for up to a year found no meaningful changes in kidney function markers.

Large observational studies have provided mixed signals, with some showing faster GFR decline in people with high protein intakes, particularly from animal sources. These studies cannot prove cause and effect, and many participants may have had undiagnosed kidney disease.

Overall, the weight of evidence suggests that for people with healthy kidneys, high-protein diets within common ranges are safe.

When high protein is a real concern

The picture changes for people with chronic kidney disease (CKD). In CKD, damaged nephrons have less capacity to adapt, and high protein intake may accelerate decline.

The National Kidney Foundation's KDOQI guidelines recommend controlled protein intake for many people with CKD who are not on dialysis, typically around 0.55–0.8 g/kg per day depending on the stage and individual factors, under medical supervision.

An estimated 1 in 7 US adults has CKD, according to the CDC, and most do not know it. This is why screening matters before adopting a very high-protein diet, especially for people with risk factors.

Key risk factors include:

• Diabetes.
• High blood pressure.
• Family history of kidney disease.
• Older age.
• Obesity and cardiovascular disease.
• History of kidney stones or long-term use of NSAIDs.

Interpreting kidney tests in athletes

Athletes can have test results that look concerning but reflect normal physiology.

If your creatinine-based eGFR looks low, ask your physician about cystatin C testing, which may give a more accurate estimate in muscular people.

Avoid intense exercise for a day or two before testing, and stay normally hydrated, to reduce temporary distortions in results.

Practical tips for a high-protein diet

For healthy people following a high-protein diet, a few practical habits help keep things in balance:

1. Drink enough fluids, especially during hot weather and heavy training.
2. Include plenty of vegetables and fruits, which help balance dietary acid load.
3. Vary protein sources, including plant proteins, fish and dairy.
4. Avoid regular high-dose NSAID use, which can harm the kidneys.
5. Get periodic blood and urine tests if you have risk factors.

For most athletes, protein intakes of 1.4–2.0 g/kg per day, as recommended by the International Society of Sports Nutrition, meet training needs. Going far above that rarely provides additional benefit.

If you have diabetes, high blood pressure or known kidney disease, discuss protein targets with your physician or a registered dietitian before increasing intake.

Editorial team conclusions

In people with healthy kidneys, high-protein diets have not been shown to cause kidney damage. The temporary increase in filtration appears to be a normal adaptation.

For people with chronic kidney disease, however, protein intake matters, and medical guidance is essential.

Because many people with CKD are unaware of it, simple blood and urine screening is worthwhile for anyone with risk factors before adopting a very high-protein diet.

Read more on our site about creatine and kidney health, how much protein athletes need, and how to interpret creatinine and eGFR results.

References

1. Devries MC, Sithamparapillai A, Brimble KS, et al. 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. J Nutr. 2018;148(11):1760–1775.
2. Antonio J, Ellerbroek A, Silver T, et al. A high protein diet has no harmful effects: a one-year crossover study in resistance-trained males. J Nutr Metab. 2016;2016:9104792.
3. Ikizler TA, Burrowes JD, Byham-Gray LD, et al. KDOQI clinical practice guideline for nutrition in CKD: 2020 update. Am J Kidney Dis. 2020;76(3 Suppl 1):S1–S107.
4. Martin WF, Armstrong LE, Rodriguez NR. Dietary protein intake and renal function. Nutr Metab (Lond). 2005;2:25.
5. Kalantar-Zadeh K, Fouque D. Nutritional management of chronic kidney disease. N Engl J Med. 2017;377(18):1765–1776.
6. Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
7. https://farmaciatletica.com/