Magnesium absorption from leafy vegetables intrinsically labeled with the stable isotope 26Mg

Five leafy vegetables were grown in nutrient solutions in which the natural magnesium was replaced by the stable isotope, 26Mg. They were fed to rats in a test meal together with the extrinsic tracer 28Mg: a) to determine to what extent the instrinsic tracer (26Mg) was exchangeable with extrinsic 28Mg during the digestion and absorption processes, and b) measure the relative Mg availability from the different vegetables. The two tracers, 26Mg and 28Mg, were close to 100% exchangeable, as judged by the ratio of 26Mg/28Mg in the livers. Mean relative Mg absorption from the various vegetables ranged from 108 to 118% of the Mg absorbed from a standard test meal containing MgSO4. There were no statistically significant differences between the rates of Mg absorption from the five vegetables although two of the vegetables tested contained oxalate. The usefulness of stable 26Mg as a tracer in Mg bioavailability tests is discussed.