If they worked you really wouldn't need to be asking this question. Can you imagine a taking a berry that helped you lose weight, it would be on the news and in every newspaper and every shop in the country would be selling them and I for one would be growing them, just another fad!
Try Googleing them Ratters, as I have never heard of them until I saw an advert on the side of this page and by all accounts they are wonderful. I`m not overweight but curious about the health benefits they claim to have.
No berry is going to make you lose weight. Acai berries contain anti-oxidents but so do most fruit. You would be just as well going to the supermarket and buying blueberries. Every few years these fashions come along. I remember going into juice bars in the States and everyone was drinking wheatgrass juice because it was supposed to be beneficial. It tasted disgusting.