Metabolic effects of two low protein diets in chronic kidney disease stage 4-5 - a randomized controlled trial

Background. International guidelines have not reached a complete agreement about the optimal amount of dietary proteins in chronic kidney disease(CKD). The aim of this study was to compare, with a randomized-controlled design, the metabolic effects of two diets with different protein content (0.55 vs 0.80 g/kg/day) in patients with CKD stages 45. Methods. Study design and sample size calculations were based on previously published experience of our group with low protein diet. The primary outcome of the study was the modification of serum urea nitrogen concentration. From 423 patients randomly assigned to the two diets 392 were analysed: 200 for the 0.55-Group and 192 for the 0.8-Group. The follow-up ranged 6-18 months. Results. Mean age was 61+/-18 years, 44% were women, mean eGFR was 18+/-7 ml/min/month. Three months after the dietary assignment and throughout the study period the two groups had a significantly different protein intake (0.72 vs 0.92 g/kg/day). The intention-to-treat analysis did not show any difference between the two groups. Compliance to the two test diets was significantly different (P < 0.05): 27% in the 0.55-Group and 53% in the 0.8-Group, with male gender and protein content (0.8 g/kg/day) predicting adherence to the assigned diet. The per protocol analysis, conversely, showed that serum urea nitrogen, similar at the time of randomization, significantly increased in the 0.8-Group vs 0.55-Group by 15% (P < 0.05). Serum phosphate, PTH and bicarbonate resulted similar in the two groups throughout the study. The 24 h urinary urea nitrogen significantly decreased after the first 3 months in 0.55-Group (P < 0.05), as well as the excretion of creatinine, sodium and phosphate (P < 0.05 vs baseline) and were significantly lower than the 0.8-Group. The prescription of phosphate binders, allopurinol, bicarbonate supplements and diuretics resulted significantly less frequent in the 0.55-Group (P < 0.05). Conclusions. This study represents the first evidence that in CKD patients a protein intake of 0.55 g/kg/day, compared with a 0.8 g/kg/day, guarantees a better metabolic control and a reduced need of drugs, without a substantial risk of malnutrition.