What it is
Refined flour: bran and germ stripped out, so most of the fiber, B-vitamins and minerals leave with them. "Enriched" means they put a few back.
Why your biology objects
Stripping the bran and germ removes the fiber that would have slowed digestion — so what's left is fast glucose with little to buffer it, spiking blood sugar much like sugar itself. Enrichment replaces ~4 nutrients out of the dozens that left.