EDIT : This thread is NOT about smoking.
I just read through http://gutsense.org and came across this :
Does smoking cause constipation?
No, not really... Actually, smoking stimulates moving the bowels because the continuous swallowing of the nicotine-laced saliva stimulates the gastrocolic reflex — an involuntary condition that initiates bowel movements.
Also, the smoke itself increases the level of CO2 in the blood. The ensuing vasodilation (widening) of the blood vessels helps intestinal peristalsis and amplifies the urge to move the bowels.
For the same reason smoking reduces the risks of constipation, smoking cessation is commonly associated with the onset of chronic constipation — the reduced stimulation diminishes the frequency and urgency of bowel movements, enlarges stools, and precipitates costivity, irregularity, straining, and fiber dependence — all of the hallmarks of latent and organic constipation.
If you are quitting smoking, you should pay particular attention to the risk of constipation, and it's prevention, but without getting hooked on fiber and/or laxatives. Study the rest of this site to proactively identify the type and stage of your constipation in order to select the best treatment and preventative approach.
Ray Peat talks about the benefits of CO2 too :
The low carbon dioxide production of hypothyroidism (e.g., Lee and Levine, 1999), and the respiratory alkalosis of estrogen excess, are often overlooked. An adequate supply of calcium, and sometimes supplementation of salt and baking soda, can increase the tissue content of CO2.