Human Calcium Absorption from Whole-Wheat Products

Abstract

Fractional calcium absorption from wheat products and the influence of co-ingested wheat products on calcium absorption from milk were measured in a series of randomized crossover studies in healthy adult women. The wheat had been intrinsically labeled with ⁴⁵Ca during growth. In the first study, fractional calcium absorption from leavened whole-wheat bread averaged 0.817 ± 0.124. By comparison, absorption from milk, ingested at a comparable load in the same women, averaged only 0.589 ± 0.111. When labeled bread was co-ingested with milk, at the same aggregate load as for bread alone, bread calcium absorption fell to 0.748 ± 0.103 (P < 0.05). In a second study, calcium absorption from an extruded cereal prepared from intrinsically labeled wheat bran was compared with milk. Calcium absorption from the cereal (0.223 ± 0.046) was significantly less than from milk (0.375 ± 0.072) (P < 0.001). When the two were co-fed at the same total load, milk calcium absorption fell to 0.258 ± 0.055 (P < 0.001). In a third study, the effect of phytate hydrolysis through yeast fermentation and of Maillard browning on calcium absorption was investigated using leavened bread and underbaked and overbaked cookies, each made with intrinsically labeled wheat flour. Calcium absorption from cookies was not affected by the extent of browning and averaged 0.652 ± 0.087. However, calcium absorption from bread in these same women averaged 0.703 ± 0.108. This was significantly more than from the cookies (P < 0.01). We conclude that absorption of calcium from wheat flour products compares favorably with absorption from milk (except in phytate-concentrated products such as wheat bran), that bran interferes with absorption of co-ingested calcium, and that leavening improves the already good absorbability of the flour-based products.