[AD]

You mentioned in another posting that caffeine did not cause much water loss. However, I have heard that it decreases the amount of water retained in the colon, and in large quantities, can lead to constipation by drying up the colon. Is this true?

 

[flux]

I don't know that it has any effect on the colonic water absorption. Caffeine's primary diuretic effect would be on the kidneys. It causes a slight water loss (1.17 ml per mg of caffeine), but because there is so much liquid in a cup of coffee in comparison (240 ml), one still gains half a cup of water.