Category: Basic Science: Stones
Introduction & Objective : Patients who depend on oral and/or enteral nutrition support to meet their nutrient needs are known to form calcium oxalate (CaOx) kidney stones. Dietary oxalate, if excessive, can contribute to CaOx stones, especially if unopposed by appropriate calcium intake. The oxalate concentration of oral/enteral nutrition formulas is not reported. We assessed various formulas for oxalate.
Methods : Adult and pediatric oral/enteral nutrition formulas commonly used at inpatient institutions as well as in home feeding regimens were selected. Formulas designed for oral and enteral consumption (or either) were included (table), but completely elemental (hydrolyzed) or modular formula products were not. Multiple samples (N, table) of each formula were acidified, heated, and centrifuged. The supernatants were filtered and analyzed for oxalate using ion chromatography. Oxalate concentration (mg/L±SD), relative standard deviation (SD) between samples (coefficient of variation; CV), and the calcium:oxalate ratio (mg:mg/L of formula) were calculated.
Results : Of 35 formulas analyzed, 9 were excluded due to inconsistent results and high CVs. Results for the 26 remaining formulas are shown (table). Oxalate concentration ranged from 4-140 mg oxalate/L of formula. Due to highly variable calcium content in the formulas, calcium:oxalate ratios varied widely (from 0-286) with lower ratios suggesting higher potential for oxalate absorption. There was no difference between the mean oxalate concentration of enteral vs. oral formulas (45 vs. 46 mg/L; P=0.92). Enteral formulas tended to have lower relative SDs (mean CV 16% vs. 21% for oral formulas), likely due to the generally more complex matrix of oral formulas, which contributed to more analytical variability. Depending on the formula used, a patient requiring 1.5 L of enteral formula daily could obtain anywhere from 12-150 mg oxalate.
Conclusions : Patients requiring oral and/or enteral nutrition support are at risk for a high exogenous oxalate load depending on the formula ingested and on the bioavailability of oxalate. Patients with a history of or at high risk for urolithiasis would benefit from strategies to reduce the bioavailability of oxalate and urinary oxalate excretion, which may include supplemental calcium with feedings or use of an appropriate lower oxalate formula.
Kristina Penniston– Scientist, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
Eve A Palmer– , Madison, Wisconsin
Riley Medenwald– , Madison, Wisconsin
Sarah N Johnson– , Madison, Wisconsin
Leema John– , Madison, Wisconsin
David J Beshensky– , Madison, Wisconsin
Ibrahim Saeed– , Madison, Wisconsin
University of Wisconsin School of Medicine and Public Health
Kristina Penniston is a scientist and registered dietitian nutritionist in Madison, Wisconsin. Dr. Penniston earned her PhD in nutritional science from the University of Wisconsin-Madison. She completed a dietetic internship at the University of Wisconsin Hospital and Clinics and is a certified dietitian member and fellow of the Academy of Nutrition and Dietetics. Dr. Penniston has provided clinical nutrition services to patients with kidney stones and other urologic diseases, such as urologic cancer and benign urologic conditions, for nearly 20 years. Dr. Penniston's research in the Department of Urology at the University of Wisconsin School of Medicine and Public Health focuses on prevention of kidney stones. Specifically, her research aims to develop and test dietary interventions that prevent or ameliorate recurrent stones; promote patients' self-efficacy in managing their stone disease; and understand and improve patients’ health-related quality of life. Dr. Penniston has developed a porcine model of dietary-induced calcium oxalate urolithiasis as a platform for studying dietary influences on stone formation. She also helped to develop the Wisconsin Stone Quality of Life questionnaire, a stone-specific instrument to assess patients' health-related quality of life. Dr. Penniston is a member of the American Urological Association and is a former research scholar (2008-2010). She has been a member of the Research on Calculus Kinetics (ROCK) Society since 2008 and is currently secretary/treasurer elect. Dr. Penniston publishes regularly in urologic and nutrition journals.