When you eat a meal, food traveling through your upper gut causes muscle to contract throughout your gut, and stool from your colon is pushed into the rectum. This is called the GASTROCOLIC reflex. This is why your morning coffee can trigger you to need to move your bowels.

Также вот здесь можно посмотреть: http://www.ncbi.nlm.nih.gov/pubmed/16109656

Вот тут также: http://arstechnica.com/civis/viewtopic.php?f=26&t=1117595

Twenty nine per cent (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, two women, eight of whom claimed coffee caused a desire to defecate (responders).

ИМХО: т.е. дефекация, стимулированная (вызванная) приемом кофе..

coffee can help people lose weight by accelerating the defecation, the movement of the large intestines can be strengthened immediately after people drink coffee, which can improve the defecation for the human body.

Read more: http://quazen.com/recreation/food/an-american-tradition-have-a-cup-of-coffee/#ixzz1IMtXAp8R