Low-protein diets do not appear to significantly improve renal function in people with type 1 or type 2 diabetic nephropathy, according to a recent meta-analysis of eight studies, each lasting more than six months. The trials involved 253 men and women with type 1 or type 2 diabetic nephropathy and 266 control subjects.

The average daily protein intake across the studies was 1.27 g/kg of body weight for the controls and 0.91 g/kg of body weight in the low-protein regimens. The low-protein subjects had more protein than is usually recommended and more than the daily recommended allowance of 0.8 g/kg of body weight but still significantly less than the control groups.

The analysis yielded the following information:

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•    Overall, low-protein diets led to a significant reduction in serum albumin (1.18 g/L), with a decline in proteinuria accompanying that reduction. Although malnutrition did not occur in any patient, the researchers noted that the continuous decrease in serum albumin concentrations would have soon led to a poor nutrition status.

•    Neither glomerular filtration rate (GFR) nor creatinine clearance changed significantly with a low-protein diet, but proteinuria did decrease significantly—by 0.69 units.

•    Seven of the eight trials showed low-protein diets to have a favorable effect on glycated hemoglobin, but the overall significant reduction in hemoglobin A1c did not slow decreases in GFR.

•    “Although these results do not rule out the possibility that a low-protein diet is beneficial for patients with type 1 or type 2 diabetes, there does not seem to be a large benefit with respect to renal function, and the potential for harm due to malnutrition should not be ignored,” investigators conclude (Am J Clin Nutr. 2008;88:660-666).