“Effect of Coffee on Distal Colon Function”, 1990 (; similar):
99 healthy young volunteers (58 men, 34 women, aged 17–27 years) answered a questionnaire concerning their bowel habit with particular reference to the effects of beverages.
29% (63% women) claimed that coffee induced a desire to defecate.
The rectosigmoid motor responses to black, unsweetened coffee were then investigated by multiport manometry in 14 healthy-subjects (12 men, 2 women), 8 of whom claimed coffee caused a desire to defecate (responders).
Results revealed an increase in motility index within 4 minutes after ingestion of both regular and decaffeinated coffee (p < 0.05) in the 8 responders, but not in the 6 non-responders. The increase in rectosigmoid motility induced by coffee lasted at least 30 minutes. There was no increase in the motility index in any subject after a drink of hot water.
These results suggest that drinking coffee can stimulate a motor response of the distal colon in some normal people.