Removing phytic acid from sorghum porridge usually improves iron absorption, but this benefit does not occur when the sorghum has high levels of tannins. In sorghum with low tannins, the improvement...
Mechanism
Synthesis from 1 study
Breaking down phytic acid frees up iron so your body can absorb it — but if tannins are there, they lock the iron away just as effectively, so your body still can't use it. That’s why removing phytic acid only helps when tannins are low.
Most probable mechanism
When phytic acid is broken down, iron becomes free and ready to be absorbed, but if tannins are present, they grab onto that iron just as tightly, making it impossible for the gut to take it in — so even after removing phytic acid, the iron still can't be absorbed.
Dietary iron in cereal porridges is initially bound by phytic acid, forming insoluble complexes that prevent iron uptake by intestinal cells.
Enzymatic degradation of phytic acid releases free iron ions into the intestinal lumen, making them available for absorption.
In high-tannin cereals, tannins rapidly bind to the newly released free iron, forming stable, insoluble tannin-iron complexes that resist dissociation under intestinal conditions.
These tannin-iron complexes cannot be recognized or transported by the iron uptake machinery on intestinal cells, blocking absorption regardless of phytate removal.
In low-tannin cereals, the absence of strong tannin binding allows free iron to be reduced to ferrous form and transported into cells via divalent metal transporter 1, increasing systemic iron availability.
Evidence from Studies
Supporting (1)
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Degradation of phytic acid in cereal porridges improves iron absorption by human subjects.
Contradicting (0)
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