Short trials saw no faster kidney decline; a longer study saw a signal
In 28 trials of 1,358 healthy adults filtration changed no faster on more protein. In 9,226 adults tracked up to 13 years the top intake quarter carried 1.32 times the risk.
What the study found
Short trials saw no faster kidney decline; long tracking saw a signal
Across 28 randomised trials in 1,358 healthy adults, filtration ended higher on more protein but changed no faster than on less. In 9,226 adults tracked up to 13 years, the top intake quarter carried 1.32 times the risk of rapid decline, a link seen only in those already filtering fast.
The caveat · Trials only in healthy kidneys
The randomised evidence applies only to people whose kidneys were healthy at the start, and early kidney disease is common and silent. Diet in the cohort came from food frequency questionnaires, which are imprecise, and its top quartile is a moderate Korean intake rather than a deliberate high-protein diet. In the cohort, a rapid decline meant the estimated filtering rate falling by more than 3 mL a minute each year, a research threshold rather than a diagnosis of kidney disease. In a sixteen-week trial at 3.2 g per kg a day, kidney and liver markers rose within the high-protein groups even though the comparison between groups came out level.
What we don't know
Short trials show filtration rising without declining; a long cohort saw a signal but read kidney function off creatinine, which protein itself raises. Nothing here shows harm, and nothing establishes safety over decades.