Updating Recommendations in Management of Dietary Phosphorous in CKD

Hyperphosphatemia, a complication found in nearly all patients with end-stage kidney disease (ESKD), is associated with increased mortality. Even in normal ranges, elevated phosphorus levels are associated with increased mortality in earlier stages of chronic kidney disease, (CKD) as well as in some patients with normal renal function.

Restriction of dietary phosphorus is a cornerstone of dietary management of patients with CKD and hyperphosphatemia. However, according to Fiona N. Byrne, BSc, MSC, PhD, and colleagues, the underlying evidence for restricting dietary phosphorous in that patient population is “weak and largely justified based on clinical experience, a preponderance of observation findings, and the suspected underlying pathophysiological mechanisms.”

The renal dietitians at the Irish Nutrition & Dietetic Institute opted to update the phosphorous section of the Irish Renal Diet Sheet, a national reference used in patient education efforts in Ireland; the sheet had been virtually unchanged for the past 20 years. The revised sheet calls for moderation in protein intake, restriction in dairy intake and in foods with a high total phosphorous content, and provides advice on the avoidance of phosphate additives.

A 1-day conference was held in 2015 to summarize advances and challenges in the management of dietary phosphorus of patients with CKD. The meeting included scientific and clinical experts from Ireland and the United Kingdom in addition to national stakeholders and 28 renal dieticians from renal units across Ireland. Seven of the dieticians attending agreed to conduct a review and dietary management update in two steps: (1) combine clinical experience and expertise with available research evidence; and (2) use the updated nutrient-level recommendations to develop a national modified diet sheet that could be individualized to the needs of each patient.

In a review article in the Journal of Renal Nutrition [2021;31(2):132-143], Dr. Byrne et al. summarized efforts to define revised dietary recommendations for phosphorus in CKD G3-5D. The group conducted a narrative review to describe the range of dietary interventions that have been examined in trials and interpret the available literature. In the literature search, they focused on nonpharmacological strategies that might improve serum phosphate control.

Identified strategies included consumption of vegetarian protein, the use of diets lower in protein, diets low in phosphorus, avoiding phosphate additives, and including egg whites and low phosphorous milks.

In some, but not all of the studies reviewed, the use of vegetarian sources including soya led to a reduction in serum phosphate. Trials of low protein intake concluded that a very low protein intake was not superior to conventional low protein intake in the effect on serum phosphate. In patients with CKD, a low phosphorus diet decreased fasting serum phosphate; although in another study, the phosphate load did not affect serum phosphate. In nondiabetic CKD patients given a high phosphorous diet, there was a significant increase in serum phosphorous. Avoidance of phosphate additives was effective in lowering serum phosphorous in a seminal study. Substituting pasteurized egg white for meat during one meal a day also appeared to be an effective diet component to lower serum phosphate.

Based on the literature review, the group agreed to include vegetarian protein, moderation of protein intake, low phosphorous intake, focus on phosphate additives, and including egg whites and milk replacers as appropriate behaviors for Irish renal patients in the revised advice.

As part of the evidence review, the researchers examined four priority topics: (1) bioavailability of dietary phosphorus; (2) the safety and benefit of increasing plant protein; (3) protein prescription and the phosphorus to protein ratio; and (4) phosphate additives. The four topics were translated into three nutrient level recommendations: (1) the introduction of some plant protein where phosphorus is largely bound by phytate; (2) consideration of protein intake in terms of phosphorus load and the phosphorus to protein ratio; and (3) an increased focus on avoiding phosphate additives.

The review resulted in three recommendations for changes in the way Irish renal dietitians manage dietary phosphorous in patients with CKD and ESKD: (1) two 7g protein exchanges of plant protein in the form of pulses and nuts, and increased intake of whole grains; (2) to ensure that patients consume sufficient protein to meet demands but not more than that, the recommendations called for more accurate prescription of protein; while the phosphorous to protein ratio was taken into consideration, it needed to be balanced against achieving variety, choice, and overall nutritional adequacy; and (3) the new recommendations called for increased focus on avoiding foods that contain phosphate additives.

In updating the national diet sheet, the dietitians combined clinical experience and expertise with available research to develop updated nutrient level recommendations. The recommendations were then used to develop a national modified diet sheet, which is individualized to the needs of each patient.

“In conclusion, our review summarized the limited evidence that supports low phosphorous dietary advice in CKD. We have also presented our interpretation of this literature in the context of our clinical experience. The lack of high-quality outcome data highlights the need for urgent research in this field, to guide clinical practice,” the reviewers said.

Takeaway Points

1. Renal dietitians from the Irish Nutrition & Dietetic Institute conducted a literature review to update the phosphorous section of the Irish Renal Diet Sheet, a national reference used to educate patients with chronic kidney disease.
2. The review included four priority topics: bioavailability of dietary phosphorous; safety and benefit of increasing plant protein; protein prescription; and phosphate additives.
3. Three recommendations emerged: introduction of some plant protein; consideration of protein intake in terms of phosphorous load; and avoiding foods containing phosphate additives.