You do not have to eat 'quite a lot of fat' with this medication, that's the whole point of it. You will experience some pretty vile side effects if you DO eat a lot of fat, and even if you think you're eating a low fat diet, Orlistat will quickly reveal the hidden fats in food, resulting again in the nasty side effects. Reduce the fat = reduce the side effects.
As others have posted, it is in now way a miracle pill, and those who take it should be carefully monitored and be prepared to commit to the kind of long term dietary changes required for successful results; and in the same way, if treated seriously and and taken correctly it does not have to be the nightmare drug that many seem to think it is.