[mrob]

In the country I live in, white flour must legally be mixed with iron. In natural foods, iron is bounds to proteins like hemoglobin or ferritin. Legally mandated iron is just "iron", which means whatever's cheapest, i.e. metallic iron powder. This is known to be poorly absorbed:

https://www.ncbi.nlm.nih.gov/pubmed/15864409

So what happens to the non-absorbed portion? I have read speculation that it could affect intestinal bacteria. Intestinal bacteria are poorly understood, but widely believed to affect human health. What happens when you start feeding them evolutionarily novel nutrients? I'm not claiming that it has any measurable effect, good or bad, but from a precautionary principle viewpoint it seems to me a bad idea.