Basically, as I understand it, when you eat food it goes through your stomach and then it travels through your bowels where the nutrients and water get gradually absorbed along the way. Coffee, as I understand it, stimulates the muscles in the bowels and causes the contents to move through the intestines more quickly. So if drinking coffee means that food will spend less time in the intestines, does that mean that less nutrients will be absorbed from the food than if no coffee was consumed?
Our bodies aren’t 100% efficient when it comes to nutrient absorption anyway, so considering there’s a number of other factors at play, it’s probably making minimal difference.
When we eat, the food added to our stomachs signals the large intestine (colon) to get a move on and make room for incoming food. Caffeine can help stimulate this response, but since most nutrient absorption occurs in the small intestine, we’re not really losing anything of value. There is some absorption in the colon, but that’s mostly water being removed so we can have formed stools instead of chronic diarrhea.