Why does coffee stimulate the need for defecation? Explain, step-by-step.

Researchers believe that the bowel-stimulating quality of coffee comes from caffeine and/or other substances contained within the coffee brew. Although there have been no large-scale studies on this subject, what we do know is that drinking coffee can stimulate movement of the colonic muscles, thus promoting peristalsis (the coordinated contraction and relaxation of intestinal muscles that causes bowel movements). One study noted that the magnitude of this peristaltic effect of caffeinated coffee is similar to one induced by eating a meal. It’s also 60 percent stronger than the effect induced by drinking water, and 23 percent stronger than the effect due to drinking decaffeinated coffee.