Adding milk to cereal porridge that has been treated to remove phytic acid reduces the amount of iron the body can absorb, even when vitamin C is present.
Mechanism
Synthesis from 1 study
Removing phytic acid frees up iron so the body can absorb it, but milk proteins grab onto that iron like a magnet and won’t let go. Even with vitamin C to help, the iron stays stuck to the milk proteins and never gets into the bloodstream.
Most probable mechanism
When cereal is broken down to remove substances that block iron, the iron becomes free and ready to be absorbed. But when milk is added, proteins in the milk stick tightly to that free iron, making it impossible for the gut to take it in — even if vitamin C is present to help.
Phytic acid in cereal binds dietary iron, forming insoluble complexes that prevent iron absorption.
Enzymatic degradation of phytic acid releases free ferrous and ferric iron ions into the intestinal lumen.
Milk proteins, particularly caseins, bind to the released free iron ions with high affinity, forming stable, insoluble complexes that are not accessible to intestinal transporters.
Iron bound to milk proteins cannot be reduced to the ferrous form by duodenal cytochrome B or transported into enterocytes via divalent metal transporter 1.
The iron-milk protein complexes remain in the intestinal lumen and are excreted, preventing systemic iron absorption regardless of the presence of enhancers like ascorbic acid.
Evidence from Studies
Supporting (1)
Community contributions welcome
Degradation of phytic acid in cereal porridges improves iron absorption by human subjects.
Contradicting (0)
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