A high-protein diet is probably not harmful in people with healthy kidneys, but in those with existing kidney problems it increases the risk of further decline. The recommendation for kidney patients is a moderate, predominantly plant-based protein diet under medical supervision.
Whether too much protein is bad for your kidneys depends strongly on whether your kidneys are healthy or not. In people with normally functioning kidneys, there is little evidence that a high-protein diet is harmful. Concerns about protein intake and kidney damage apply primarily to people who already have a kidney problem.
One mechanism that can occur with high protein intake is glomerular hyperfiltration: the small filtering units in your kidneys (glomeruli) start working harder than normal. In healthy people, this appears to be temporary and probably harmless. But if you already have fewer functioning filtering units -- for example due to existing kidney disease or a congenital abnormality -- this overload can, over time, lead to kidney damage.
In people with chronic kidney disease (CKD), a high-protein diet does carry genuine risks. It has been linked to accelerated decline in kidney function, accumulation of nitrogen waste products in the blood, metabolic acidosis (acidification of the blood), inflammation, and bone problems. In addition, excessive protein in this group also raises the risk of cardiovascular disease, oxidative cell damage, elevated phosphate levels in the blood, and disruption of the gut microbiome.
Pay attention to phosphate as well: a high-protein diet often brings a large amount of phosphate with it, through meat, dairy, and ultra-processed products. Chronically high phosphate intake has been linked to loss of kidney function and increased cardiovascular risk, even in people without existing kidney disease.
The opposite is equally a pitfall. Too little protein in kidney patients leads to loss of muscle mass and a worse overall prognosis. The recommendation is therefore not an extreme choice in either direction, but an individually tailored diet -- preferably with a predominance of plant-based protein sources -- under the guidance of a dietitian or physician. A specific at-risk group is children born with only one kidney: for them, excessive protein and salt intake is explicitly discouraged.
The claims are based on multiple studies (PMID 25979491, 35409969, 31728497, 40739997, 37394104, 35365815, 35511366, 35713730). The strength of evidence ranges from limited (for healthy individuals) to moderate (for CKD patients). There are few large randomised trials; much of the evidence is observational or mechanistic.