Low-protein diets in chronic renal insufficiency: a meta-analysis
ACP J Club. 1992 July-Aug;117:11. doi:10.7326/ACPJC-1992-117-1-011
Fouque D, Laville M, Boissel JP, et al. Controlled low protein diets in chronic renal insufficiency: meta-analysis. BMJ. 1992 Jan 25;304:214-8.
To determine whether low-protein diets delay renal death (either the need to start dialysis or patient death) in patients with chronic renal failure.
MEDLINE files from 1975 to 1991, abstracts from the International Society of Nephrology and the American Society of Nephrology, and data solicited from investigators were reviewed.
Only randomized controlled trials of low-protein diet and its effect on progression of renal insufficiency were included. Diabetic nephropathy trials were excluded. 46 studies were reviewed, and 6 were selected for analysis (4 published articles, 1 published abstract, and 1 unpublished study).
890 patients (496 men) with mild to severe chronic renal failure were included from the 6 studies (450 patients treated; 440 controls). Authors supplied missing data. Analysis was by intention-to-treat.
The study populations were clinically heterogeneous in age, sex ratio, level of renal insufficiency, and incidence of renal death in the control group (range, 0.14 to 0.78). The degree of protein restriction also varied. Reduction of protein intake was at least 0.35 g/kg body weight per day for patients in 4 studies and 0.2 g/kg per day for the other 2. The 2 studies with the most stringent restrictions added a ketoacid supplement to the diet of the patients in the treatment groups. Renal death was defined as initiation of dialysis or patient death. Follow-up was 12 to 24 months. 5 of the 6 trials showed a decrease in renal death in the intervention group, but in only 1 study was the difference statistically significant. For the pooled analysis, the intervention groups had 61 renal deaths in 450 patients and the control groups had 95 deaths in 440 patients (common odds ratio, 0.54; 95% CI, 0.37 to 0.79; P < 0.002). There was no statistically significant heterogeneity in the odds ratios from the 6 trials (P > 0.2).
Low-protein diets delay renal death. Further trials are needed to estimate the effect of low-protein diet on the rate of progression of renal insufficiency, nutritional risks and benefits of protein restriction, the optimal level of protein restriction, and the need for nutritional supplements.
Source of funding: Not stated.
Address for article reprint: Dr. D. Fouque, Service de Néphrologie, Hôpital Edouard Herriot, 69437 Lyon Cedex 03, France.
Fouque and colleague's review of 6 randomized trials suggests that the prescription of low-protein diets to patients with chronic renal failure can prolong the course of the disease and delay the onset of dialysis. Locatelli and colleagues (1), however, the authors of the largest of these studies, concluded that low-protein diets were of marginal benefit and probably not worth the sacrifice and negative effect on quality of life.
The clinical course of the patient with chronic renal disease does not end with dialysis but continues after dialysis and transplantation. The major predictors of success on dialysis are adequacy of dialysis and the nutritional status of the patient as measured by serum albumin, serum creatinine, and protein catabolic rate (a measure of dietary protein intake) (2). Current studies do not address the long-term nutritional implications of low-protein diets, nor do they delineate the degree of protein restriction that prolongs the course of chronic renal failure but preserves body cell mass and maintains positive nitrogen balance that favors long-term patient survival. Additional studies are needed to examine the details and measure effects on quality of life before protein restriction, especially severe protein restriction, becomes standard practice.
Michael N. Hartnett, MD
Northwest Renal Clinic, Inc. Portland, Oregon