How does caffeine (or any additional agents) act as a laxative when ingested? I'm interested in the metabolic/signaling pathway.
Coffee does have an effect on the peristaltic movement in the bowel.
Effectively, decaf and regular coffee stimulate peristaltic movement in the colon as effectively as a meal does. Caffeine is not the active agent then, but some other compound in coffee.
Source: Boekema PJ, Samsom M, et al. Coffee and gastrointestinal function: facts and fiction. A review. Scand J Gastroenterol Suppl. 1999;230:35-9. PMID 10499460.