Dietary Phosphate Prescription and Survival in Dialysis Patients

“CUTTING DIETARY PHOSPHATE DOESN’T SAVE DIALYSIS PATIENTS’ LIVES” is the latest headline in nephrology news. So does that mean the struggles to control your phosphorus are no longer important?

The study titled “The Association between Prescribed Dietary Phosphate Restriction and Mortality among Hemodialysis Patients” by Lynch, et al is in the online December 2010 issue of the Clinical Journal of the American Society of Nephrology. According to the findings, ‘Dietary phosphate prescription was not associated with improved survival in hemodialysis patients and in some subgroups there may be greater mortality.’ In other words, having a lower phosphorus diet prescription does not necessarily mean hemodialysis patients live longer. The range of blood phosphorus values was similar for all the diet groups (3.8-7.9 mg/dL). Of note, analysis of subgroups with greater survival reveals that participants with phosphorus below 5.5 mg/dL still had a survival advantage.

Finding of the study include:

• Patients on lower phosphate diets did not live longer than patients on higher phosphate diets. Were there other factors to consider? Generally dietary phosphate level is determined by patient’s size, protein requirement and phosphorus levels.
• Even though the group of patients who were not prescribed a phosphate restriction showed a trend toward greater survival it was not statistically significant.
• This study analysis was based on data from the Hemodialysis Study from 1995-2001. Today patients are challenged with a food supply loaded with phosphate additives.
• Greater phosphate restriction can result in lower albumin due to limiting higher protein foods. Patients on the more restricted low phosphate diet prescription (below 1000 mg) were more likely to have poorer nutritional status and need for nutrition supplements.

 Restricting dietary phosphorus means eating less dairy and meat. These foods are sources of high quality protein  as well as other nutrients. Whole grain products, nuts and seeds, legumes, and chocolate are hi in phosphorus, but also contribute valuable nutrients and plant chemicals. Though beyond the current study evaluation, consider the many unanswered questions on this topic.

• Are there essential chemicals that are omitted from a dialysis diet due to the phosphorus prescription?
• Do the lower phosphorus foods recommended to kidney patients, such as refined breads, cereals and grains, higher sugar and fat containing foods, and limited fresh fruits and vegetables contribute to a decreased survival?
• What are the long term effects of a phosphorus restricted diet? but also the effects of the renal diet overall?
• Is there a cut-off point between a healthy low phosphorus diet and a level that restricts too many foods, making it impossible to obtain nutrients and dietary components necessary for good health?
• If a more liberal phosphate diet becomes the preferred option for the future, do we choose more dialysis, more phosphate binders, or both for future prevention and treatment of hyperphosphatemia?
• Does the phosphate diet prescription reflect the actual dietary intake for most dialysis patients?
• What is the impact of the growing use of inorganic phosphate additives in processed foods? Is there a benefit to focusing on eliminating these lower nutrient dense phosphate sources instead of foods with a greater organic phosphate content but higher nutrient density?

Additional research is definitely needed before throwing your low phosphorus diet out the window!