For me the side effects never lasted more than a day or two after I stopped eating it. I suppose everyone's digestive system is different and some people would be more sensitive but your body tends to flush things out pretty quick.
Chemists create olestra by combining two naturally occurring substances, sucrose and vegetable oil, to form a molecule that is not found anywhere in nature. Yet the resulting synthetic molecule tastes just like real fats do! Fat is what makes candy bars and french fries so filling (and fattening). With olestra, you get the taste of the fat without any of the calories of the fat, because your body has no way to digest olestra.