Influence of Sourdough Fermentation-Induced Dephytinization on Iron Absorption from Whole Grain Rye Bread–Double-Isotope Crossover and Single-Blind Absorption Studies

Journal article, 2025

Background/Objectives: There are substantial beneficial health effects from a diet rich in whole grains. However, a high intake of whole grain, and hence a high intake of the iron absorption inhibitor phytate, may result in the impaired bioavailability of non-heme iron. The study examined non-heme iron absorption in healthy women from two portions (80 g and 120 g) of identical whole grain bread, baked with or without phytate-degrading techniques. Methods: The study included two single-blinded iron isotope trials. Subjects were served meals containing whole grain rye bread, which was either baked from scalded flour or sourdough-fermented flour labeled with ⁵⁵Fe or ⁵⁹Fe. The absorption of non-heme iron from the meals was measured through the erythrocyte incorporation of radioiron isotopes. Results: Iron absorption from the 80 g high-phytate bread was 7.0 ± 4.1% (mean ± SD, n = 8). Iron absorption from the 80 g dephytinized bread was 19.1 ± 15.1% (mean ± SD) and thus on average 2.8 times higher compared to the absorption from the high-phytate bread (p = 0.001). Iron absorption from the 120 g high-phytate bread was 4.6 ± 2.9% (mean ± SD, n = 17). Iron absorption from the 120 g dephytinized bread was 15.0 ± 9.2% (mean ± SD) and thus on average 3.5 times higher compared to the absorption from the high-phytate bread (p = 0.001). Conclusions: Iron uptake was significantly higher from dephytinized bread compared to scalded bread. And the higher the amount of phytate, the higher the beneficial effects on iron absorption from dephytinization.