Why is unleavened bread more healthful than leavened bread?

There is no evidence that unleavened bread is more healthful than leavened bread. In fact, the leavening agent in bread, which is usually yeast, can actually improve its nutritional value. For example, yeast is a good source of B vitamins, including thiamine, riboflavin, and niacin. Additionally, the fermentation process that occurs when yeast is added to bread dough can increase its bioavailability of minerals such as iron and calcium.