I'm not sure about their weightloss benefits, but they do have a dense nutritional composition. I'm led to believe that grapefruit, pineapple and artichoke (jerusalem) have fat-busting properties.
I don't like the taste of the juice, but the berries are said to have various medicinal properties. They'd probably help with weight loss if taken with a low-fat diet and exercise, but the latter two on their own are the only right way to lose weight.