Eating in response to digestive fatigue rather than true hunger overworks the stomach and wears out the digestive organs.

Original passage

These unpleasant symptoms are felt because nature has accomplished her work at an unnecessary outlay of vital force and is thoroughly exhausted. The stomach is saying, “Give me rest.” But with many the faintness is interpreted as a demand for more food; so instead of giving the stomach rest, another burden is placed upon it. As a consequence the digestive organs are often worn out when they should be capable of doing good work.