The answer is that if you follow Alli instructions you will count calories and exercise which would probably cause weight loss anyway. The thing that gives it the extra oomph is that Alli prevents the absorption of dietary fat which can cause some antisocial side effects. You are advised to limit the fat in your diet to about 200 calories and to skip Alli if you eat a meal without. The more fat you eat, the more severe the side effects. For example if you have a fast food meal, you better have a change of clothing. So a low calorie, fat free diet with exercise will cause weight loss. The Alli regimen is different because you can eat some fats, get the benefit of the flavor without the fat calories sticking around. Of course there is the possibility that with flatulence and explosive diahrhea (?) nobody will stick around.