According to the International Coffee Organization, 1.6 billion cups of coffee are consumed around the world every single day. (See Reference 1) Can all this coffee consumption in the kitchen be causing a problem in the bathroom?
Coffee: A Stimulating Way to Start the Morning
Having a bowel movement shortly after drinking a cup a coffee may be because of the caffeine in the coffee. Caffeine is a stimulant (See Reference 2, paragraph 1) and it can stimulate the bowels causing them to contract and move waste out of the body. (See Reference 3) And while coffee can stimulate a bowel movement, it is not normally the cause of diarrhea.
What else is in that coffee?
Adding milk or milk products may contribute to diarrhea in someone who is lactose intolerant or sensitive. (See Reference 4, What causes diarrhea? section) Also, sugar substitutes can cause diarrhea. (See Reference 5, What causes diarrhea? section)
If you are experiencing loose bowel movements for more than a couple days, see your doctor. (See Reference 6, Points to Remember section, 7th bullet)