My husband was, about the time he started smoking. He trying to quit now, with hopes that his IBS will subside.
Yes, it is, because smoking stimulates saliva secretion. In turn, smoke-laced saliva gets swallowed, and stimulates the secretion of gastric juices, the gastrocolic reflex, and peristaltic mass movement — the precursors to abdominal cramps and/or diarrhea. That's, incidentally, why people are told not to smoke on an empty stomach.