Continuing on with a brief discussion of the landmark MDRD Study: at the time of the study, several smaller studies suggested that a low protein diet would prolong time to ESRD for patients with CKD. The theory was that low dietary protein would lead to (a) less buildup of nitrogenous wastes which might contribute to uremia, (b) improved acidosis normally associated with advanced CKD, and (c) less proteinuria and thus less ongoing renal damage.
The MDRD Study took several hundred patients with moderate CKD (GFR = 25-55 cc/min) and advanced CKD (GFR = 13-24 cc/min) and subjected them to a 2x2 prospective randomized control design. They tested the effect of both usual-protein versus a low-protein diet (defined as 0.58 g of protein per kg of body weight per day) as well as having both high BP target and low BP target groups. The average follow-up time in this study was just over 2 years. For the most part, there were no major differences in any of the groups in terms of rate of progression to ESRD. Effects of the low-protein diet were seen, however: in the moderate CKD group, those randomized to the low protein diet actually showed a transiently DECREASED GFR over the first 4 months of the study, only to demonstrate a slower rate of decline at later time points. The authors described this graph by stating that the initial decrease in GFR is due to hemodynamic effects which over the long run actually have beneficial effects (kind of like ACE-inhibitors' effect on the kidneys). So although the results of the trial were essentially negative for any effect of a low-protein diet on slowing CKD progression, there are many who believe that had the patients been followed out for an even longer period of time, the benefit would ultimately manifest.