Decreasing Intakes & Absorption of Phosphorus in Haemodialysis Patients Through Food Choices (DIP HD)

Based on new evidence renal dietitians in Ireland are revising the diet sheet that is used to teach patients about reducing blood phosphate. Changes that renal dietitians plan to make to the dietary phosphorus prescription Inclusion of some nuts and pulses More detailed education re phosphate additives More accurate protein prescription Inclusion of more whole grains Encouraging the use of foods with a low phosphorus to protein ratio The investigators want to test the two diet prescription to find out, which one is better at reducing blood phosphate and which one is more acceptable to patients. The investigators also want to make sure it is safe.

Background: Chronic Kidney Disease (CKD) afflicts one in twenty Irish citizens who are over age 45 and is a significant risk factor for cardiovascular disease, premature death and significantly impacts healthcare utilisation. As kidney function deteriorates, phosphorus, upregulates counter regulatory hormones (immunoreactive Parathyroid Hormone (iPTH) and Fibroblast Growth Factor 23 (FGF23), the elevated levels of which are maladaptive. Collectively these abnormalities and their complications are referred to as Chronic Kidney Disease, Mineral & Bone Disorder (CKD MBD). Hyperphosphataemia or high blood phosphate levels is associated with increased mortality, in dialysis patients, in the earlier stages of CKD and even in patients with normal renal function. The use of phosphorus restricted diets in combination with oral phosphate binders has become well established in the management of patients with CKD stages 3-5 (including CKD stage 5D). Experts have called for research into the dietary management of phosphate in the CKD population. The current evidence base is weak and in a recent Cochrane systematic review the authors concluded that there was limited low quality evidence to indicate that dietary interventions may positively affect CKD-MBD. In recent years there has been increased focus on dietary phosphorus restriction in the management of CKD-MBD and a number of experts have suggested changes in how we manage dietary phosphorus. Several potential strategies have been suggested and in response the Renal Interest Group (RIG) of the Irish Nutrition & Dietetic Institute (INDI) held a 1 day meeting in Dublin in January 2015 which brought together numerous experts in the field to summarise our current understanding and the recent advances in the field. Following on from this, RIG set up a working group to translate the new knowledge from the advanced study day and from further literature reviews into a modified low phosphate diet sheet. Almost all people who have end stage kidney disease (ESKD) and require dialysis to survive, follow a dietary phosphorus restriction, to control high blood phosphate, with the aim of reducing the risk of cardiovascular disease, fractures and death. Research Hypothesis: The modified low phosphate diet sheet is superior to current treatment in haemodialysis patients Study Objectives Primary Objective: To determine if the modified low phosphorus dietary prescription is superior to current management in reducing serum phosphate levels in HD patients Secondary Objectives To determine if the modified low phosphorus diet is tolerable To determine if the modified low phosphorus diet is safe To determine if the modified low phosphorus diet brings the renal diet closer to healthy eating advice e.g. increased fibre intake.

As with most education based interventions compared to routine care it is difficult to reliably mask either the subjects or the investigators to the proposed intervention. We will attempt to blind patients referring only to the diets as diet A and diet B and avoiding the use of terminology such as old and new. We will reprint the dietary information for both arms so they do not resemble current illustrated formats.

Patients randomised to the standard care arm will be re educated using the current low phosphorus diet prescription.

Patients randomised to the intervention arm will be educated using a modified low phosphorus diet prescription.

Routine / Standard Care: Routine dietary intervention is currently provided by one-to-one counselling to the subject and his/her relevant family members or carers, by a state registered dietitian regarding a diet which provides <15mg Phosphorus /g Protein (over the day). This is equivalent to approximately 1000mg P / day. This is based on the 'Eating Well with Kidney Disease' dietsheet produced by the Renal Interest Group (RIG) of the Irish Nutrition & Dietetic Institute (INDI) in 2010 and includes following main components: Restricting protein intake to requirements (1-1.2g/kg Ideal Body Weight) Restricting dairy intake (1-1.5 portions per day) Avoiding foods high in phosphate Avoiding foods with phosphate additives

Modified Low Phosphorus Diet Prescription: The new prescription recommends five changes to current management Introduction of some plant protein in the form of pulses and nuts where the phosphorus is largely bound by phytate Increased focus on avoiding additives Introduction of more whole grains e.g. wholemeal sliced pan/ pasta/rice . Avoiding over-prescription of protein which carries an obligatory phosphorus load. Focus on high protein foods with a low phosphorus to protein ratio

Difference in serum phosphate value at 1 month v baseline, in those randomised to the modified diet compared to the difference in serum phosphate value at 1 month v baseline in those randomised to standard care.

Between arm difference in dietary phosphate intake (separating phosphate into high & low bioavailability). Between arm difference in dietary fibre intake.

Difference in serum iPTH value at 1 month v baseline, in those randomised to the modified diet compared to the difference in serum iPTH value at 1 month v baseline in those randomised to standard care.

Within subject change in geometric mean FGF-23 measurement at baseline as compared to the end of the 1 month intervention. Because of evidence that subjects with diabetes handle phosphorus differently we will analyse result for FGF 23 separately in patients with and without diabetes (Muras et al., 2013, Yoda et al., 2012).

Check serum potassium in week 2. Difference in serum potassium value at 1 month v baseline, in those randomised to the modified diet compared to the difference in serum potassium value at 1 month v baseline in those randomised to standard care.

Inclusion Criteria: >18 years Self reported urine output less than 2 cups (400mls) / day On maintenance haemodialysis for > 3 months Phosphate >1.6mmole/L on average of last 3 available routine monthly blood tests Exclusion Criteria: Hyperkalemia, defined as a predialysis serum K on routine monthly blood test of >6mmoles/l in the month preceding the trial. Parathyroidectomy Corrected serum calcium <2.2 or > 2.6mmol/L or local normal units where ranges varied significantly from 2.2-2.6mmoles/l. Acute concurrent illness, requiring hospitalisation in the 2 weeks prior to recruitment.

Byrne F, Gillman B, Renal Interest Group INDI, Eustace J. Multicentre Randomized Control Trial of Phosphate Control with a Modified as Compared to Standard Renal Diet TH-OR030. J Am Soc Nephrol 2018;29:8.