Long-term effect of modification of dietary protein intake on the progression of diabetic nephropathy: a randomised controlled trial

AIMS/HYPOTHESIS: There is currently insufficient evidence to recommend a low-protein diet for type 2 diabetic patients with diabetic nephropathy. We assessed whether a low-protein diet could prevent the progression of diabetic nephropathy. METHODS: This was a multi-site parallel randomised controlled trial for prevention of diabetic nephropathy progression among 112 Japanese type 2 diabetic patients with overt nephropathy. It was conducted in Japan from 1 December 1997 to 30 April 2006. The participants were randomly assigned using a central computer-generated schedule to either low-protein diet (0.8 g kg(−1) day(−1)) and normal-protein diet (1.2 g kg(−1) day(−1)), and were followed for 5 years. The participants and investigators were not blinded to the assignment. The primary outcomes were the annual change in estimated GFR and creatinine clearance, the incidence of doubling of serum creatinine and the time to doubling of baseline serum creatinine. RESULTS: The study was completed by 47 (84%) of 56 participants in the low-protein diet group and 41 (73%) of 56 participants in the normal-diet group. During the study period, the difference in mean annual change in estimated GFR between the low-protein diet and the normal-protein diet groups was −0.3 ml min(−1) 1.73 m(−2) (95% CI −3.9, 4.4; p = 0.93). The difference in mean annual change in creatinine clearance between the low-protein diet and the normal-protein diet groups was −0.006 ml s(−1) 1.73 m(−2) (95% CI −0.089, 0.112; p = 0.80). A doubling of serum creatinine was reached in 16 patients of the low-protein group (34.0%), compared with 15 in the normal-protein group (36.6%), the difference between groups being −2.6% (95% CI −22.6, 17.5; p = 0.80). The time to doubling of serum creatinine was similar in both groups (p = 0.66). CONCLUSIONS/INTERPRETATION: It is extremely difficult to get patients to follow a long-term low-protein diet. Although in the low-protein group overall protein intake was slightly (but not significantly) lower, it did not confer renoprotection. Clinical trial registration: ClinicalTrials.gov NCT00448526 Funding: Research grant from the Ministry of Health, Labour and Welfare of Japan ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00125-009-1467-8) contains supplementary material, which is available to authorised users.