Effects of phytate and minerals on the bioavailability of oxalate from food

Abstract

Phytate and mineral cations are both considered as important dietary factors for inhibiting the crystallisation of calcium oxalate kidney stones in susceptible individuals. In this paper, the phytate and mineral composition of whole bran cereals (wheat, barley and oat) and legumes were determined together with their soluble and insoluble oxalate concentrations in order to investigate the effects on oxalate solubility. The oat bran sample had the highest soluble oxalate concentration at 79±1.3mg/100g, while total and soluble oxalate concentrations in the food samples studied range from 33 to 199mg/100g and 14 to 79mg/100g, respectively. The phytate concentration was in the range from 227 to 4393mg/100g and the concentrations of cations were in the range 54–70mg/100g for calcium, 75–398mg/100g for magnesium, 244–1529mg/100g for potassium and 4–11mg/100g for iron. Soluble oxalate concentration did not increase in proportion to total oxalate, and the phytate concentration in all foods was sufficient to contribute to an increase in soluble oxalate concentration by binding calcium.