Protein intake and your kidneys: does high protein harm kidney function?

"Too much protein is bad for your kidneys." You have surely heard it, maybe even from someone in a white coat. For healthy athletes who deliberately eat high protein, that is a stubborn myth, and one you should not let slow you down. The real story is more nuanced, and more reassuring, than the warning suggests.

My stance: with healthy kidneys, a high protein intake is not a problem, but it does colour a few of your blood values. Once you know which, you will not be startled by your result.

Does a lot of protein harm your kidneys?

In healthy adults, a high-protein diet does not measurably change kidney function. A meta-analysis of 28 studies with more than 1,300 participants found no difference in the change in filtration rate between people on high or low protein (Devries, 2018). A full year of markedly high protein in trained men likewise showed no harmful effects (Antonio, 2016).

An important nuance: this is about healthy kidneys. Anyone who already has a kidney condition falls under different advice and should tune protein intake with a doctor or dietitian. The Dutch Kidney Foundation (Nierstichting) is clear on this: with reduced kidney function, protein restriction can be useful, but for healthy people it is not needed.

What protein does do to your blood values

A high-protein diet can raise your urea, because urea is a breakdown product of protein. That is a normal consequence of your diet, not a sign of damage. Your creatinine can also read a little higher, especially if you combine a lot of muscle mass with creatine. The table below lays out the effects.

How much protein is sensible?

The Netherlands Nutrition Centre (Voedingscentrum) uses a guideline of roughly 0.8 grams of protein per kilo of body weight per day for healthy adults. Strength athletes deliberately sit above that, often around 1.6 to 2.0 grams per kilo for muscle maintenance and growth, and for healthy kidneys that is amply justifiable. Do drink enough water, because with a lot of protein your kidneys have to excrete more nitrogen.

If you combine a high protein intake with creatine, you will see both effects in your creatinine. That is expected and no cause for concern with healthy kidneys.

Where does the protein myth come from?

The worry that protein is bad for your kidneys is not pulled out of thin air, but the advice has been mistranslated. In people with an existing kidney condition, a high protein intake can put extra strain on the kidneys, which is why they are sometimes advised to limit protein. That is correct for that group. The error is carrying that advice over to healthy people, whose kidneys process the extra nitrogen without trouble.

On top of that comes the confusion with the creatinine value. An athlete with plenty of muscle and a high-protein diet sees their creatinine read a little higher, reads "reduced kidney function", and concludes the protein is to blame. In reality it is the combination of muscle mass and the way the eGFR formula calculates. Telling apart "my value is higher" from "my kidneys work worse" is exactly where it goes wrong. The Dutch College of General Practitioners (NHG) guidelines therefore advise doctors never to judge kidney function on a single marker, but to include cystatin C and the context of the person.

How to keep an eye on your kidneys

Do not judge your kidneys on creatinine or urea alone. Add cystatin C, because that marker does not depend on your protein intake or your muscle mass (Baxmann, 2008). Measure it together with creatinine and urea. Our kidney health blood test bundles those markers, so you can track your trend.

Read on: the pillar blood values for strength athletes, plus high creatinine from muscle mass and creatine and your blood values.

My advice: do not let yourself be scared off plenty of protein if your kidneys are healthy. Drink enough, add cystatin C for certainty, and discuss a persistent deviation with your GP.

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. The Journal of Nutrition. 2018. PMID: 30383278.
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. Journal of Nutrition and Metabolism. 2016. PMID: 27807480.
3. Baxmann AC, Ahmed MS, Marques NC, et al. Influence of muscle mass and physical activity on serum and urinary creatinine and serum cystatin C. Clinical Journal of the American Society of Nephrology. 2008. PMID: 18235143.
4. NHG (Dutch College of General Practitioners), Voedingscentrum and Nierstichting, public information on protein intake and kidney function.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. For treatment decisions, discuss your results with your GP.