This is one of the most persistent nutrition myths, and it contains a real, narrow truth wrapped in a much broader false generalization.
The narrow truth
For people who already have chronic kidney disease (CKD), reducing protein intake is genuine, standard clinical guidance — because damaged kidneys have a harder time clearing the nitrogenous waste products of protein metabolism, and easing that load can slow disease progression. This is where the "protein is hard on your kidneys" idea originally comes from, and in that specific population, it's accurate.
What doesn't hold up
The generalization to healthy people is not supported by the evidence. Multiple controlled studies and systematic reviews — including research specifically looking at protein intakes well above the RDA in healthy, resistance-trained individuals over periods of a year or more — have found no evidence of kidney damage from high protein intake in people with normal kidney function to begin with. A frequently cited 2018 systematic review in the Journal of the American Society of Nephrology and multiple sports-nutrition-focused studies since have reached the same conclusion.
Why the confusion persists
High protein intake does increase glomerular filtration rate (GFR) — your kidneys filter more fluid, a normal physiological adaptation, comparable to how your heart rate increases during exercise. Early research interpreted this adaptive increase as a sign of "strain" or damage. Longer-term studies since haven't found that this adaptation translates into actual kidney injury markers in people with healthy kidneys.
The practical takeaway
If you have known kidney disease, follow your nephrologist or renal dietitian's specific protein guidance — it will very likely be lower than the general athletic recommendations elsewhere on this site, and that's appropriate for your situation. If you have no diagnosed kidney condition, the current evidence doesn't support avoiding higher protein intake out of kidney-safety concerns. If you have risk factors (diabetes, hypertension, family history) but no diagnosis, a conversation with your doctor before deliberately pushing protein intake very high is a reasonable, low-cost precaution.