Reduction of dietary protein and phosphorus in the modification of diet in renal disease feasibility study

Abstract

Objective and design The Modification of Diet in Renal Disease (MDRD) Feasibility Study was designed to test procedures and evaluate the feasibility of a full-scale clinical trial aimed at assessing the effects of reduction of dietary protein and phosphorus on progression of renal disease.Setting and subjects Ninety-six patients with chronic renal insufficiency were randomly assigned to different diets in one of two studies depending on their glomerular filtration rate.Intervention The diets contained three different protein and phosphorus levels: moderate diet=1.3 g protein per kilogram per day and 16 to 20 mg phosphorus per kilogram per day; low diet=0.575 g protein per kilogram per day and 5 to 10 mg phosphorus per kilogram per day; and very low diet with keto or amino acids=0.28 g protein per kilogram per day and 4 to 9 mg phosphorus per kilogram per day. Eighty-five patients were monitored for at least 6 months; maximum follow-up was 22 months.Main outcome measures Compliance with study diets was measured monthly using urea nitrogen appearance and 3-day diet diaries plus one 24-hour recall. The main outcome measure was change or maintenance of glomerular filtration rate.Statistical analyses performed Data were analyzed by analysis of variance and paired t tests.Results Mean dietary protein intake, as determined by urea nitrogen appearance, decreased significantly in participants assigned to the diets low and very low in protein and phosphorus (P<.05). Overall, the follow-up protein intake (based on urea nitrogen appearance) as a percentage of baseline ranged from 45.8% to 83.1%. Analysis of diet diaries showed better dietary adherence than indicated by urea nitrogen appearance. Review of the exchange methodology used in dietary instruction suggests that imprecision of the exchange lists may have been a factor in the difficulty study participants had in achieving ±10% of the target protein goal.Applications Based on the MDRD Feasibility Study, the protocol for the full-scale study was modified to include protein counting instead of food exchange methodology to monitor protein intake.