Why do prunes make you regular, but plums don't?

Answer 1

Actually, they do. It's just that the fiber in prunes is more concentrated because the water has been removed. Plus, you usually eat one or two plums, but a handful (five to eight) prunes.

Answer 2

Given that plums still contain so much more water than prunes, I would recommend caution as plums may very well make you far more regular than perhaps you think now. While prunes may have an immediate effect on you, regularly consuming any kind of fruits will help you maintain regularity.