Please take a note and always remember that plum is one of those food products that works as a natural laxative if consumed in large quantities (four~five fruits in a row is usually enough to get the imminent effect), and the effect comes especially fast if this product is consumed in the form of a natural freshly squeezed juice, so don't overdo it (250ml of juice once each 12 hours is usually absolutely fine) unless you deliberately wish to sit in the WC for a couple hours straight. Otherwise, there's nothing bad in it.

P.S. Bananas actually work the exactly same way, although you have to consume way bigger quantities of them (than plums) to get the laxative effect relatively fast (like, at least eight bananas in a row, which even the most gluttonous people usually don't do).