- Click here for explanation of classification scheme.

The purpose of this study was to use a meta-analysis to assess the efficacy of dietary protein restriction in previously published studies of diabetic and nondiabetic renal disease.

• Randomized controlled trial design
• Mean length of follow-up of more than 1 year
• Included information on the number of patients who develop renal failure or died

• Published in English

• Studies with unpublished results
• Did not use an adequate control group

Recruitment

Studies were identified through MEDLINE, references in review articles and published studies, and other papers written by the authors of the published trials.

Studies selected for review were RCT for nondiabetics with kidney disease and RCT or time-controlled studies with nonrandomized cross-over design for diabetic nephropathy.

Design

A meta-analysis was done on English-language medical literature published from January 1966 through December 1994 for studies examining the effect of low-protein diets in humans with chronic renal disease.

Blinding used (if applicable) Not applicable

Intervention (if applicable)

Nondiabetic Renal Disease: Subjects received a low-protein diet ranging from .4 g/kg/day to .6 g/kg/day or a usual-protein diet. The mean duration of follow-up in each study ranged from 18 months to more than 36 months.

Diabetic Nephropathy: Subjects received a low-protein diet ranging from .5g/kg/day to .85g/kg/day. The mean duration of follow-up in each study ranged from 9 to 33 months.

Statistical Analysis

The overall effect of the studies were calculated by using both the random-effects model and a fixed-effects model. The data was presented as a risk ratios with 95% CIs. Heterogeneity in relative risk among studies was assessed by using the chi-square test.

Timing of Measurements

The meta-analysis was done on English-language medical literature published from January 1966 through December 1994.

Dependent Variables

• Glomerular filtration rate
• Creatinine clearance
• Serum Creatinine
• Albumin excretion rate

Independent Variables

• .4g/kg/day to .6g/kg/day
• .5g/kg/day to .85g/kg/day
• Usual protein intake

Control Variables

Initial N:  1413 subjects in 5 studies of nondiabetic renal disease and 108 subjects with type 1 diabetes in 5 studies.

Attrition (Final N):  Dropout rate ranged from 1.8% to 38.3% in the nondiabetic renal disease studies and the dropout rate ranged from 0% to 41% in the diabetic nephropathy studies

Age:  not stated

Ethnicity:  not stated

Other relevant demographics:  not stated

Anthropometrics:  not stated

Location:  Worldwide studies published in English language

Other findings

Studies done in nondiabetics:  Pooled results showed that dietary protein restriction significantly reduced the risk for renal failure or death (RR, 0.67, CI: 0.50 to 0.89; P<0.007) compared with usual protein diet. The pooled mean arterial pressure was only –2.9 mm Hg (CI, -10.4 mm Hg to 4.9 mm Hg) for the low protein group.

Studies done in those with diabetes: Pooled results showed that dietary protein restriction significantly reduced the risk for decline in GFR or creatinine clearance or increase in urinary albumin excretion rate. Relative risk, 0.56 (CI, 0.40 to 0.77; P<0.001).

Between diet groups, the difference in pooled mean arterial blood pressure was –2.6 mm Hg (CI -6.1 mm Hg to 1.0 mm Hg) and the difference in HgA1c was 0.03%, CI, -0.58% to 0.65%.

 

Dietary protein restriction effectively slows the progression of both diabetic and nondiabetic renal diseases. Dietary protein restriction significantly reduced the risk for renal failure or death.

The beneficial effects of the low protein diet were not related to blood pressure in diabetics or non-diabetics or to differences in HgA1c in diabetics.

University/Hospital:

University of California Irvine, New England Medical Center

Even though the prescribed protein level was 0.4 to 0.6 g/kg/d in the studies reviewed, the dietary intakes of protein were closer to 0.7 to 0.8 g/kg/d.

All studies in subjects without diabetes and in subjects with diabetes showed a beneficial effect of low protein diets in slowing the progression of renal disease. The number of subjects represented in studies of those with diabetes was small with 8 to 35 subjects in each study. The studies were of sufficient duration to evaluation the effects of a low protein diet.