Tighter protein restriction found to offer no advantage in delaying progression to renal failure.

Very low-protein diets do not delay progression to renal failure in CKD patients any better than low-protein diets and may even increase patients’ risk of death, a study finds.

Vandana Menon, MD, PhD, and Mark J. Sarnak, MD, MS, of Tufts Medical Center in Boston, and colleagues analyzed long-term follow-up data from 255 participants in the Modification of Diet in Renal Disease Study. They had an average age of about 51 years; 86% were white.

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Subjects mainly had stage 4 nondiabetic CKD. The original study, which was conducted from 1989 to 1993, examined the effect of dietary protein restriction and BP control on kidney disease progression. Investigators randomized subjects to receive a low-protein diet (0.58 g/kg/day) or a very low-protein diet (0.28 g/kg/day) supplemented with keto acids and amino acids.

In long-term follow-up, kidney failure developed in 227 subjects (89%), 79 died (30.9%), and 244 (95.7%) reached the composite end point of kidney failure or death, the researchers reported in the American Journal of Kidney Disease (2009;53:208-217). The median duration of follow-up until kidney failure, death, or administrative censoring was 3.2 years and median time to death was 10.6 years.

In the low-protein group, 117 patients (90.7%) had kidney failure, 30 (23.3%) died, and 124 (96.1%) reached the composite outcome. In the very low-protein group, 110 (87.3%) had kidney failure, 49 (38.9%) died, and 120 (95.2%) reached the composite outcome. In adjusted analyses, the very low-protein diet had no impact on delaying progression to kidney failure or the composite outcome, but it was associated with an almost twofold increased risk of death at any time point and a greater than twofold increased risk of death following kidney failure.

“Although very low-protein diets generally are not recommended,” the investigators wrote, “we believe these findings are clinically relevant given the continued interest in the use of dietary protein restriction as an intervention to delay progression of kidney disease.”

The study’s strengths include random assignment to dietary protein groups and long-term follow-up. Limitations include a lack of dietary protein intake and nutritional measurements as well as information about medical management and clinical course during the long-term follow-up.