Examining natural and added phosphorus intake in dialysis patients

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PROJECT SUMMARY End-stage renal disease (ESRD) patients treated with maintenance hemodialysis (HD) are encouraged to follow several dietary recommendations related to dietary phosphorus (P) intake in light of the evidence that hyperphosphatemia is associated with increased mortality in these patients. ESRD patients are advised to have a maximum of 800 to 1000 mg of dietary P per day, but these recommendations do not distinguish between different types of dietary P. There are two types of P in food: (1) natural or organic P that is bound to proteins and found in foods that are high in protein, and (2) added or inorganic P that does not naturally occur but is added as a preservative in processed foods such as colas, deli meats, cereals, and processed cheeses. The added inorganic P is more readily absorbed through the digestive system and may have a greater influence on hyperphosphatemia in ESRD patients than an equal amount of organic P. Ethnic and cultural influences often mediate dietary food choices. Compared to Whites, African Americans may have greater intake of high protein foods and may be more likely to eat processed food with added inorganic P. The differences in dietary P intake across racial/ethnic groups of HD patients are not well studied. Renal dietitians play an integral role in the management of dietary P intake in HD patients. We dietitians are responsible for communicating nutrition therapy recommendations while also being sensitive to patients' personal and cultural food preferences and explore the underlying factors related to adherence to a low-P-diet. Different assessment tools may result in major differences in estimating P and its subtypes, and race may have a role in these differences and their impact on occurrence of hyperphosphatemia. The paucity of reliable patient-centered assessment of dietary intake of P through identification of key foods and analysis of actual food intake among different racial/ethnic groups in HD patients is a major gap in our understanding. As a Black renal dietitian and PhD student, I am committed to studying these important questions. I plan to examine the hypothesis that different dietary P assessment methods yield different estimates and that dietary P intake of HD patients is different across race/ethnicity. To do so, I will assess dietary P intake and sources of dietary P by a food frequency questionnaire in 450 HD patients and through a 3-day diet record with interview in a randomly selected subgroup of 120 patients. I will also examine the hypothesis that estimated P intake by diet record is more strongly associated with hyperphosphatemia than estimates from FFQ, and that African American HD patients by virtue of eating more processed food with higher added inorganic P have higher likelihood of hyperphosphatemia. My proposed 3-year study will enable me to address an important gap, and my project also has the potential to inform kidney disease nutrition education materials, which would allow us to provide more efficient and culturally sensitive nutrition counseling to kidney disease patients in order to improve their adherence to P intake recommendations. I plan to use this valuable data for my doctoral dissertation.