Iron absorption is impaired by:

Question

BlackTom AI · Accepted Answer

Phytates (inositol hexaphosphate) bind dietary iron in the intestinal lumen and form insoluble complexes, preventing its uptake by enterocytes.

1) Relevant knowledge points and concepts
- Two forms of dietary iron: haem (from animal hemoproteins) and non‑haem (plant sources, iron salts). Haem iron is absorbed intact via a different pathway and is highly bioavailable. Non‑haem iron absorption is influenced by dietary enhancers and inhibitors.
- Enhancers: vitamin C (ascorbic acid) reduces ferric (Fe3+) to ferrous (Fe2+) iron and forms soluble complexes that increase uptake via DMT1 transporters.
- Inhibitors: phytates (found in whole grains, legumes, nuts, seeds), polyphenols, tannins, calcium and some proteins (e.g., in unfermented soy) can reduce non‑haem iron absorption.

2) Step‑by‑step reasoning
- Option b (phytates): Phytate chelates Fe3+ and Fe2+, forming insoluble phytate–iron complexes at gut pH, so iron cannot be absorbed by enterocytes. Chemical representation: phytate + Fe3+ → phytate–Fe (insoluble complex). This directly impairs iron absorption.
- Option a (haem): Haem iron is absorbed well and increases bioavailable iron; it does not impair absorption—so (a) is incorrect.
- Option c (vitamin C): Vitamin C enhances non‑haem iron absorption by reducing Fe3+→Fe2+ and keeping iron soluble—so (c) is incorrect.
- Option d (protein): Generally, meat protein (the “meat factor”) enhances iron absorption; although some plant proteins (e.g., soy phytoproteins) can inhibit, the term “protein” alone is not a primary inhibitor—so (d) is incorrect.

3) Why the correct answer is correct
Phytates are a well‑established dietary inhibitor: they chelate iron into insoluble forms that cannot cross the intestinal epithelium, lowering bioavailability, especially of non‑haem iron in plant‑based diets.

Conclusion: The best choice is b. phytates, which matches the provided correct answer.

Iron absorption is impaired by:单项选择题

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