Chemical leavening agents like soda or baking powder are harmful to the stomach.

Original passage

The use of soda or baking powder in breadmaking is harmful and unnecessary. Soda causes inflammation of the stomach and often poisons the entire system. Many housewives think that they cannot make good bread without soda, but this is an error. If they would take the trouble to learn better methods, their bread would be more wholesome, and, to a natural taste, it would be more palatable.