In Practice
Balancing Nutrition and Serum Phosphorus in Maintenance Dialysis

https://doi.org/10.1053/j.ajkd.2014.01.429Get rights and content

Elevated serum phosphorus levels are common in patients with chronic kidney disease and are associated with heart and vascular disease, conditions that in turn are associated with increased mortality. Accurately managing phosphorus intake by restricting dietary protein alone can prove challenging because protein from different sources can contain varying amounts of available phosphorus. Additives used in processed foods frequently are high in inorganic phosphorus, which is readily absorbed, compounding this difficulty. Recent evidence suggests that dietary protein restriction in some cases may do more harm than good in some patients treated with maintenance hemodialysis because protein restriction can lead to protein-energy wasting, which is associated with increased mortality. Accordingly, phosphorus binders are important for managing hyperphosphatemia in dialysis patients. Managing hyperphosphatemia in patients with late-stage chronic kidney disease requires an individualized approach, involving a combination of adequate dietary advice, phosphate-binder use, and adjustments to dialysis prescription. We speculate that increased use of phosphate binders could allow patients to eat more protein-rich foods and that communicating this to patients might increase their perception of their need for phosphate binders, providing an incentive to improve adherence. The aim of this review is to discuss the challenges involved in maintaining adequate nutrition while controlling phosphorus levels in patients on maintenance hemodialysis therapy.

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Case presentation

A 63-year-old white man with stage 5D chronic kidney disease (CKD) started on maintenance hemodialysis (HD) therapy 2.5 years ago. He presents with the following laboratory measurements (fasting midweek predialysis): serum phosphorus, 6.2 mg/dL (1.90 mmol/L); serum calcium, 10.4 mg/dL (2.60 mmol/L); serum parathyroid hormone (PTH), 280 pg/mL; serum 25-hydroxyvitamin D3 (25[OH]D3), 40 ng/mL (100 nmol/L); normalized protein catabolic rate, 1.25 g/kg/d; and serum albumin, 3.8 mg/dL. His medications include

Protein intake and serum phosphorus

A common recommendation for the management of hyperphosphatemia is to reduce the amount of phosphorus in the diet.2 The NKF-KDOQI guidelines and European Best Practice Guidelines recommend daily phosphorus intake of 800-1,000 mg/d for patients on maintenance HD therapy.3, 6, 7 Foods with high protein content tend to have high phosphorus content, and an increase in dietary protein has been shown to correlate with an increase in serum phosphorus levels (Fig 2).8 Limiting dietary phosphorus intake

Inorganic phosphorus

Inorganic phosphorus additives are an often-overlooked source of phosphorus in the diet. Compounds that contain inorganic phosphorus frequently are used in the food industry to extend shelf life, enhance flavor, and improve the color of food products; these additives can make the overall phosphorus content very high.13 However, it is not a requirement that manufacturers list phosphorus content on food packaging, making the exact levels of phosphorus in these foods difficult to determine.

Risks associated with low dietary protein intake

The NKF-KDOQI guidelines suggest that patients receiving HD aim to consume 1.2 g of protein per kilogram per day, and the European Best Practice Guidelines recommend at least 1.1 g of protein per kilogram per day.4, 7 However, a study of 53,933 patients receiving HD in clinics across the United States showed that >50% of these patients consumed less than this amount.16 This study further demonstrated that a spontaneous decrease in protein consumption in patients with a normalized protein-nitrogen

Phosphate-binder use and adequate nutrition

By reducing the amount of dietary phosphorus absorbed from the gut, phosphate binders help control serum phosphorus levels and are used by 78%-88% of patients receiving HD.1, 18 Table 1 compares binding capacities and dosages of 4 of the leading phosphate binders in the United States: calcium acetate, calcium carbonate, sevelamer carbonate, and lanthanum carbonate. The values presented are estimates of the dosage that would be required in order to control a relatively modest increase in

Additional benefits associated with phosphate binders

One of the complications of CKD is an increased risk of heart disease, and a key risk factor for heart disease is vascular calcification. Although the pathogenesis of vascular calcification in patients with CKD is thought to be multifactorial, hyperphosphatemia is an important risk factor.20 In certain patients, hypercalcemia also may contribute to the progression of calcification, and recent guidelines have suggested that the use of calcium-based phosphate binders is not recommended for some

Phosphate binders in clinical practice

One of the key challenges in the treatment of chronic diseases is patients' adherence to their diet and drug regimen. The majority of patients on maintenance HD therapy require phosphate binders; however, on average, 51% of patients are not fully adherent to their prescribed phosphate-binder therapy.37 It therefore is important to consider how best to help patients with CKD follow their often complex therapy regimens.

There are no clear demographic predictors of nonadherence. In a systematic

Conclusions

Restricting dietary protein to help control phosphorus levels in patients undergoing maintenance HD may be more harmful than beneficial. More importantly, increased awareness of inorganic phosphorus in food additives may lead to significant improvements in dietary phosphorus restriction regimens.

Phosphate binders help maintain serum phosphorus levels in the recommended ranges and have beneficial effects in terms of reducing calcification and serum FGF-23 levels. In addition, taking phosphate

Acknowledgements

Support: This article is based on information presented at a Shire-sponsored symposium, Clinical Challenges in Balancing Nutritional Intake and Phosphate Metabolism in Dialysis Patients, held at the European Renal Association–European Dialysis and Transplant Association Congress 2012 (ERA–EDTA 2012, Paris, France, May 25-27, 2012). Rosalind Morley at PharmaGenesis London provided medical writing services funded by Shire, including full editorial support, collating information from the

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