EXTRINSIC VS INTRINSIC LABELING OF THE CALCIUM IN WHOLE-WHEAT FLOUR

Fractional absorption of calcium from bread made either from intrinsically or extrinsically labeled whole-wheat flour was compared in 11 healthy adult women. The intrinsic label was provided by Ca-45 injected individually into stems of wheat plants during growth. The extrinsic lag was introduced by adding Ca-45 to unlabeled flour via the water used in dough making. The two labeled breads were tested in a randomized crossover design using a standardized breakfast administered after an overnight fast. Approximately 80 g labeled bread was consumed by each subject, providing a total calcium load of 13.3 mg. Fractional absorption from the intrinsically labeled bread averaged 0.812 +/- 0.130 (xBAR +/- SE) and from the extrinsically labeled bread 0.792 +/- 0.113. The mean difference, within subject, was only 0.025 +/- 0.016 and was not significantly different from zero. Extrinsic labeling of the calcium of whole-wheat flour results in a degree of labeling homogenity equivalent to that of intrinsic labeling, at least for a leavened bread product.