I noticed years ago while feeding my newborn that she would chug some delicious warm milk and fill up that diaper. Since then I always figured the coffee phenomenon was related.

Drinking plain warm/hot water can trigger the same response so it is arguably not just coffee.

I vary my routine a lot, so I am pretty sure that it is the liquid coffee here that is the trigger. Not just caffeine because I normally use caffeine pills instead.

It's a pretty strong effect for me, but IIRC there are multiple causes, like that it's hot + acidic + caffeinated.

It's hard to discount other factors but I certainly notice a difference switching from water to coffee.

I can drink as much coffee as I want and I experience no laxative effects. But if I eat some chilli peppers next morning I feel like I am going to explode.

On some days I'm 8-10 times a day coffee drinker and on the same days I turn out to be 4-5 times a day pooper. I suspect there is some connection.

I think it's because it pulls water into the intestines, which helps you poop easier.