Actually it is the grain.
Commercial bread is made without yeast because it takes too long to leaven.
The dough is whipped to introduce air bubbles before baking. Regular wheat doesn't have enough protein to hold the air bubbles. Think egg whites - high protein level means it can form the structure required to hold lots of air. To remedy this they started breeding very very high protein levels into the wheat.
Wheat protein has been linked to diseases outside of the gut, such as asthma, multiple sclerosis and arthritis.
https:// www.medicalnewstoday.com/articles/313514.php