The quality of the evidence is downgraded by study limitations (high or unclear risks of bias), by imprecise results (small studies and wide confidence intervals), and by inconsistency (unexplained heterogeneity).
A Cochrane review «Protein restriction for diabetic kidney disease»1 «Jiang S, Fang J, Li W. Protein restriction for diabetic kidney disease. Cochrane Database Syst Rev 2023;1(1):CD014906. »1 included 8 studies with a total of 486 subjects comparing low protein diet (LPD: 0.6 to 0.8 g/kg/day) wih unrestricted protein diet (UPD: ≥ 1.0 g/kg/day). Most studies were not designed to examine death or kidney failure. A low protein diet did not have effect on death (RR 0.38, 95% CI 0.10 to 1.44; 5 trials, n=358), kidney failure (RR 1.16, 95% CI 0.38 to 3.59; 4 trials, n=287), or decline of glomerular filtration rate over time (MD -0.73 mL/min, 95% CI -2.3 to 0.83; 7 trials, n=367). There was no evidence of malnutrition. Participant compliance with a LPD was unsatisfactory in nearly half of the studies.