Higher Protein May Not Harm Kidney Function
A 10-year study using directly measured kidney function found no evidence that higher habitual protein intake accelerated kidney decline in generally healthy middle-aged and older adults.
Higher protein intake has long raised concerns about putting extra pressure on the kidneys. But a new 10-year study found no meaningful association between habitual protein intake and declining kidney function in adults who largely started with healthy kidneys.
The important caveat is equally clear: these findings should not be applied to people who already have chronic kidney disease.
Study Details
Researchers analyzed 1,324 adults from the Norwegian Renal Iohexol Clearance Survey. Participants were around 64 years old on average, and most did not have chronic kidney disease, diabetes, or established cardiovascular disease when the cohort was established.
Average reported protein intake was about 1.2 grams per kilogram of body weight per day. The highest quarter of participants averaged approximately 1.8 g/kg/day, while the lowest averaged about 0.8 g/kg/day.
Methodology
One feature makes this study particularly useful.
Instead of relying only on creatinine-based estimated GFR, researchers repeatedly measured kidney filtration using iohexol clearance, a more direct way of measuring glomerular filtration rate. Creatinine measurements can be influenced by factors such as muscle mass and diet, potentially complicating studies of protein intake.
Participants were followed for a median of 10 years. Protein intake was estimated using a detailed 261-item food-frequency questionnaire.
Key Findings
Each additional 0.1 g/kg/day of protein was associated with essentially no difference in annual measured GFR decline, at -0.01 mL/min/1.73 m² per year.
Higher protein intake was not associated with accelerated kidney-function decline.
Among participants starting with measured GFR of at least 60, higher protein intake was not associated with developing measured GFR below 60 during follow-up.
Results remained broadly consistent across multiple analyses.
What This Means
The study does not prove that unlimited protein is safe.
What it does challenge is the idea that otherwise healthy adults should restrict protein specifically because moderate-to-high protein intake will inevitably damage their kidneys.
That distinction matters as people increasingly consume more protein to preserve muscle during aging, support resistance training, or maintain lean mass during weight loss.
The researchers themselves caution that they did not specifically study very high protein supplementation of the kind sometimes used by strength athletes. They also could not separate plant protein from animal protein, and diet was self-reported.
Implications for Practice
For clinicians counseling adults with preserved kidney function, these results provide some reassurance that habitual protein intake within the ranges observed in this population does not appear to be a major driver of age-related kidney-function loss.
But this should not change protein recommendations for patients with established CKD.
Current KDIGO guidance recommends approximately 0.8 g/kg/day for many adults with CKD and advises avoiding protein intake above 1.3 g/kg/day in people with CKD who are at risk of progression.
So the practical message is simple:
Healthy kidneys and diseased kidneys should not be treated as the same nutritional problem.
This study weakens the argument for routine protein restriction as a strategy to prevent kidney disease in otherwise healthy adults. It does not eliminate the need for individualized protein management once kidney disease is present.