The investigators purpose is to research the impact of the simultaneous use of a new dialysis membrane with higher permeability for medium and protein bound uraemic toxins (medium cut-off dialysis membrane Theranova®) combined with diet modification to reduce the level of inflammation in chronic dialysis patients. The investigators hypothesize that the use of a medium-cut off dialysis membrane and dietary modification work synergistically and cause a significant and clinically meaningful reduction in inflammation levels compared to on-line hemodiafiltration with a high-flux dialysis membrane.

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 Interleukin-6. Secondary outcome is the serum concentration of interleukin-10, serum amyloid A, High-sensitivity C-reactive protein, total leukocyte count and plasma concentration of bacterial 16s rDNA. 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 hospital 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.

Inclusion Criteria:

• Patient on chronic hemodialysis or hemodiafiltration for at least 12 weeks;
• Age 18 years old or more;
• A functioning arteriovenous fistula or graft as a permanent dialysis vascular access;
• Being able to give an informed consent to participate in the survey

Exclusion Criteria:

• Planned kidney transplantation, transition to peritoneal dialysis or to another dialysis center within 12 weeks of the start of the study
• Acute febrile inless 4 weeks prior to study inclusion
• Active chronic inflammation (e.g., an active autoimmune disease or an open wound), chronic ongoing infection or cancer
• New cardiovascular or cerebrovascular event 4 weeks prior to study inclusion
• Clinically malnourishet patient and/or BMI below 19 kg/m2 and/or loss of more the 5% of body mass in the last 3 months
• Immunosuppressive treatment
• Expected survival of less than 1 year
• Pregnancy or breast-feeding
• Indication for dietary supplements to increase calorie and/or protein intake
• Specific indication for carrying out hemodiafiltration instead of hemodialysis as per attending physician
• Serum albumin concentration <32 g/l after screening to enter the study
• Inability to follow the study diet or test procedures
• Rapid reduction of residual renal function in the period prior to entry into the study
• Intolerant of on-line haemodiafiltration (infusion intolerance)

Plan to share IPD that underline results published in the manuscripts reporting study results.

From the time of publication of associated manuscripts for 10 years.

Available on demand from the investigators.