Enriched wheat flour is not necessarily bad for one's health, but it does lack a number of nutrients and fiber found in whole wheat flour. It may have negative effects on a person's glycemic index due to a lack of fiber as well.
Enriched wheat flour is commercially produced whole wheat flour. The commercial manufacturing process removes the bran and the germ of the wheat berry, leaving behind a starchy endosperm. This wheat flour lacks a number of vital nutrients, including magnesium, iron, zinc, calcium and the B vitamins. It also lacks fiber, which helps digestion and helps lower the glycemic index of the wheat. A lower glycemic index means that whole wheat flour does not raise blood sugars as much as enriched white flour.
In order to help counter some of the negative effects of removing all of the nutrients, the flour is enriched by adding iron, calcium and the B vitamins back into it; however, not as much of these nutrients may be returned to the flour as were removed from it.
If looking for a wheat flour that is the healthiest, consider purchasing a whole wheat flour. This still contains much of the bran and germ that provide more nutrients, fiber and protein.