My DSis does slimfast and has really good success on it. She did it last summer and lost 13 lbs I believe. (That was all she needed to lose! The brat!)She usually has a shake for breakfast and a bar for lunch. She follows the diet plan on the box. It recommends having a piece of fruit for a snack between bfast and lunch and between lunch and dinner or you can have a snack bar, I believe. I'm not totally sure on what the box says. But then she eats a dinner. And sometimes not the best dinner and she usually loses weight. About 2 lbs a week. And she says if she sticks to it faithfully for 3 days she loses.
Hope that helps. I personally feel starving on it. But sometimes when I look at my DSis I think Hey If I can look like that maybe I should try again!! But I'm doing WW and doing pretty good. Down 22lbs!!!
Good luck!!!