It does block some of the fat. The fat then exits your body with oily stool, runny stool, oily discharge if you happen to eat a higher fat meal and also you will have a strong urge to use the bathroom and when you get the urge don't wait cause your body won't. The doc. recommended guidelines for diet when taking Xenical are pretty specific concerning caloric intake and fat intake so make sure you follow those and make sure that your doctor knows you're taking it because if you have any kind of gall bladder problems, digestive tract problems, liver problems and there's a couple of others that I can't remember off the top of my head, the Xenical can cause serious complications even death. I was told this not only by the Xenical Rep. when I first started taking it, but it was also printed in the info that the manufacturer sent me with my new patient packet. The bottom line is if you follow their guidlines for fat intake and caloric intake you will lose the weight without spending the money on the pills. Something else to consider. I was told by my doc. a couple of years later (when discussing the different weight loss drugs) that when taking the Xenical as with others you have to be sure to take supplements because it doesn't differentiate between good fat and bad fat therefore a person can actually lose some of the nutritive quality (vitamins, minerals etc..) from their food when taking it because the body expels it right along with the fat.