Absorption of selenium from milk protein and isolated soy protein formulas in preschool children: studies using stable isotope tracer 74Se.

Absorption of selenium as the stable isotopic tracer [74Se]selenite was measured in four preschool children who were receiving liquid formula diets based on casein, isolated soy protein, and a 50:50 combination of the two protein sources. The children were in continuous ambulatory balance studies within the Clinical Research Center during three consecutive 11-day collection periods. The enrichment of the 74Se/76Se ratio in feces was measured by radiochemical neutron activation analysis, with fractional absorption estimated therefrom. Mean fractional absorption of selenium (+/- SD) from the formulas based on milk, isolated soy protein, and milk-soy were 64.2 +/- 14.6, 73.4 +/- 19.0, and 45.0 +/- 10.9%, respectively, with the combined formula having a significantly lower intestinal uptake for added selenite than the casein formula. Stable isotopes of selenium are safe and potentially useful tools for examining its bioavailability in the diets of young children.