I think you've figured out half the reason why orlistat works - the fear factor is certainly true.

The other is the reduction in absorption of fat. If you eat 45g of fat a day and orlistat blocks 15g (about a third) and the calories in a gram of fat is 9, then simple maths will mean that 135 calories are not digest. Might not seem much per day but on top of the reduction in calories from changes in diet another nearly 1000 calories a week can only aid the weightloss process.

Kitty