If you train seriously, you have probably heard it: lots of protein and creatine are supposedly bad for your kidneys. It sounds logical, because your kidneys process the waste from protein. But for healthy kidneys the story is a lot more nuanced than the gym myth suggests.
The main misunderstanding sits in one word that means two things: creatine and creatinine. They look alike, but are not the same.
Creatine versus creatinine: the big misunderstanding
Creatine is the supplement many athletes take for strength and muscle building. Creatinine is the waste product your kidneys filter and that appears on your blood result. If you use creatine, your creatinine in the blood can rise a little, simply because there is more supply.
That usually does not mean your kidneys work less well. It is more of a measurement effect: the value goes up, but your filter function is simply fine. How creatinine and the eGFR connect is in our piece on creatinine and eGFR.
Important to mention to your doctor: if you use creatine, say so. Then a slightly raised creatinine can be read in the right context, and you avoid needless worry.
Is a lot of protein bad for your kidneys?
For people with healthy kidneys, there is no strong evidence that a high protein intake causes lasting damage. Many athletes eat plenty of protein for years without problems. A protein-rich meal can, though, temporarily raise your creatinine and urea a little.
| Factor | Effect on your values | Meaning |
|---|---|---|
| Creatine supplement | Can raise creatinine a little | Often a measurement effect, no damage with healthy kidneys |
| Protein-rich meal | Can temporarily raise creatinine and urea | Temporary; mention it for a clean measurement |
| Heavy training | Can briefly raise creatinine | Muscle breakdown, not necessarily kidney damage |
The nuance: for those who already have a reduced kidney function, this is different, and caution with very high protein is wise. That is why it is useful to know your baseline values.
What should you watch as an athlete?
A few things deserve attention, even with healthy kidneys. Drinking enough is part of it, certainly if you sweat a lot and eat protein. Be careful with large amounts of anti-inflammatory painkillers around heavy training, because they can strain your kidneys.
And watch out with unknown performance agents or heavy courses. Some supplements and agents from the strength-sport scene are not harmless for your organs. What that does to your hormones is in our pillar on hormonal health in men.
What does a blood test actually say then?
A kidney test measures your creatinine and calculates your eGFR. For an athlete that is useful to have a baseline value, so you know what is normal for you. A single measurement just after heavy training or a lot of creatine can distort, so pick a calm moment.
The Kidney Function panel maps your kidney values. The broader picture of your kidneys is in our pillar on kidney function in men. Always discuss an abnormal result with a doctor.
Frequently asked questions
Should I stop creatine before a blood test?
Not necessarily, but know that creatine can raise your creatinine a little. If you want a clean picture of your kidney function, you can consider pausing it a few days before, or simply mention it to your doctor. Then your value is read in the right context.
Is a protein shake bad for my kidneys?
For healthy kidneys there is no strong evidence for that. A protein shake in itself is usually no problem, though a lot of protein can temporarily raise your creatinine and urea a little. If you already have a reduced kidney function, discuss your protein intake with your doctor or dietitian.
Should I drink extra water if I eat a lot of protein?
Drinking enough is wise anyway, and with a high protein intake it helps your kidneys excrete the waste. You do not need to overdo it, but let your fluid intake grow with your training and your sweat loss. Clear urine is usually a good sign, and with healthy kidneys this is just part of training well.
Sources
- Nierstichting. Nutrition and your kidneys.
- Thuisarts.nl. I have a reduced kidney function.
- Voedingscentrum. Protein and exercise.
Disclaimer
Caliberhealth works with BIG-registered doctors who review your blood results. This article provides general information and is not a substitute for medical advice from a GP or specialist. A blood test is a tool, not a diagnosis in itself. For serious or persistent symptoms, contact your GP, or call 112 in an emergency.
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