Oxalate Content of Enteral Nutrition Formulas

Patients requiring oral and/or enteral nutrition support, delivered via nasogastric, gastric, or intestinal routes, have a relatively high incidence of calcium oxalate (CaOx) kidney stones. Nutrition formulas are frequently made from corn and/or or soy, both of which contain ample oxalate. Excessive oxalate intake contributes to hyperoxaluria (>45 mg urine oxalate/day) and CaOx stones especially when unopposed by concomitant calcium intake, gastrointestinal malabsorption is present, and/or oxalate degrading gut bacteria are limiting or absent. Our objective was to assess the oxalate content of commonly used commercial enteral nutrition formulas.

Enteral nutrition formulas were selected from the formulary at our clinical inpatient institution. Multiple samples of each were assessed for oxalate concentration with ion chromatography.

Results from 26 formulas revealed highly variable oxalate concentration ranging from 4 to 140 mg oxalate/L of formula. No definitive patterns for different types of formulas (eg, flavored vs unflavored, high protein vs not) were evident. Coefficients of variation for all formulas ranged from 0.68% to 43% (mean ± SD 19% ± 12%; median 18%).

Depending on the formula and amount delivered, patients requiring nutrition support could obtain anywhere from 12 to 150 mg oxalate/day or more and are thus at risk for hyperoxaluria and CaOx stones.