The investigators will carry out a prospective interventional randomised study to compare achieved serum concentrations of selected protein bound uremic toxins by dialysis with a medium cut-off membrane (Theranova, Baxter AG, USA) and online hemodiafiltration with a standard high-flux dialysis membrane. In the second phase, both dialysis purification methods will be supplemented by a change in the diet with increase of the daily intake of dietary fiber to 30g and addition of a short-chain fatty acid propionate in the dose of 1 g daily.~The main outcome of the study is the serum concentration of p-cresol sulphate. Secondary outcome is the serum concentration of indoxyl-sulphate and trimethylamine-N-oxide (TMAO). Serum albumin concentration and lean body weight of patients represent safety outcomes for this study.~This investigator-initiated research project has been entirely planned and will be conducted by the clinical researchers in a tertiary University Medical Center Ljubljana.~The study will include 50 chronic prevalent stable dialysis patients in the following periods:~2 weeks of wash-in period with standard bicarbonate haemodialysis and standard high-flux dialysis membrane,~then the patients will be randomized in a 1:1 ratio to either one of the two study arms:~(interventional study arm) 4 weeks of dialysis with medium cut-off (Theranova) membrane (first phase), then dialysis for 4 weeks with the same membrane and increased fiber intake (second phase),~(control study arm) 4 weeks of dialysis with a high-flux membrane using on-line haemodiafiltration (first phase) and 4 weeks of high-flux membrane haemodiafiltration and increased fiber intake (second phase),~finally, all patients will undergo a 4 week wash-out period with a standard bicarbonate haemodialysis using standard high-flux dialysis membrane identical to wash-in period.~Measurement of the study end-points will be carried out at the end of 2-week wash-in period, each 4-week period and at the end of 4 week wash-out period.
The study will compare achieved levels of protein-bound uremic toxins with dialysis using a medium cut-off membrane compared to the treatment by online haemodiafiltration with a high-flux dialysis membrane. In the second phase of the study dietary fiber and short-chain fatty acid intake will be increased to verify a possible additional reduction in the levels of protein bound uremic toxins.