How do lipase inhibitors stop the fat in the diet being absorbed?

Orlistat: Orlistat is lipase inhibiter and is used to loose weight in over weight individuals with low fat, low calorie diet and exercise.So fat is in not absorped in its entirity and is passed undigested in stools.So total calorie absorption is reduced and because of the side effects which are not pleasant people cut down on their fat intake and that helps too.