It has long been thought that higher protein diets adversely affect kidney function, but evidence does not actually support this claim, even for most people with existing kidney disease. (A recent blog article covered this issue in more detail.) Various renal biomarkers may be altered by a higher protein intake, but these changes have been determined to be physiological rather than pathological. The biomarkers assessed included urinary pH, serum urea and uric acid, GFR, urinary albumin excretion, and others. The researchers wrote, “For none of the outcomes was a ‘convincing’ certainty of evidence found for detrimental effects of HPI [high protein intake] with regard to the development of kidney diseases.”
The review included multiple randomized controlled trials (RCTs). Protein intake ranged from 1.0 to 3.3 g/kg of body weight per day in the higher protein groups compared to 0.3 to 2.6 g/kg body weight/day in the control groups, or from 12.5 to 40% of total energy intake for the higher protein group versus 5.4 to 24% in the control group, or from 123 to 150 g/d (higher protein) versus 46 to 75 g/d (control). It’s interesting that protein intakes above 0.8 g/kg/day are still considered “high,” when this cutoff has been so highly questioned, and when evidence suggests a higher amount is likely needed for optimal health in adults. (The oft-cited “0.8 g/kg” daily protein recommendation was based on maintaining nitrogen balance, not on maintaining robust health.)
High dietary protein intake is not typically considered a risk factor for kidney disease. To the contrary, considering the strong connections between type 2 diabetes, hypertension, and kidney disease, the dietary factor most likely to contribute to kidney disease when consumed in excess is refined carbohydrate. Elevated blood glucose and hypertension are among the diagnostic criteria for metabolic syndrome, driven by chronic hyperinsulinemia – and restricting dietary carbohydrate, not protein, has been shown to reverse metabolic syndrome.