Ok, this is long, but...
One of the problems w/ Slimfast is the type of weight that you lose. It's all about body mechanics.
When you lose weight on the Slim fast plan, it is just that - weight. You are not losing just fat, per se. You will initially dump water weight, then some (SOME) fat, then muscle. The loss of water weight lasted probably around 7 days or so. At the same time, your body was tapping into your fat stores for energy. At some point, your body will sense that you are in a famine situation and preserve fat; your metabolism will slow proportionately slowing fat loss even more. Since you are exercising while slim-fasting, your body will use up consumed carbs first for energy, then will turn to lean tissue (muscle mass) for energy. Since lean tissue weighs more than fat, the weight-loss continues to 'look good' as your body shrinks. Problem is, your muscles will have zero shape, metabolism will suck, and an underlying layer of fat will make you look soft and squishy. The reasons people plump back up after a Slim-Fast diet are many, among them being lack of dietary knowledge and reverse body mechanics.
Reverse body mechanics is the opposite of what I put above: once your body senses that the famine is over and food is plentiful, it will restore some lost muscle tissue AND store more fat for the next famine....just in case.
To lose weight properly, diet, exercise, and supplementation must work in concert. You must eat more frequently - 5 to 7 times a day - and eat proper meals. Smaller portions of better foods. Limit intake of refined carbs (sugar, white flour and rice). More veggies. Healthy protein (white fish, lean chicken & beef, egg whites, and whey). Exercise at an optimal time for weight loss and maximize the opportunity for your body to create lean tissue (which burns more calories) by eating about 1g of protein per lb of lean body weight and weight training. Use a good multivitamin and an ephedrine-free fat loss catalyst to round out your program.
All the parts need to be in place to prevent the post-weightloss ballooning.
A similar trap to fall into would be the Subway ("He's Henry, Clay Henry") weight loss plan where you eat a 6 inch sub for lunch and a 12 inch veggie sandwich for dinner. I've read Jared's weight loss plan...he dropped his caloric intake down to around 1200 calories - way below a normal person's base metabolic rate - and basically starved himself into being slim. One of the greatest lies on television was, "lookin' buff, Jared"

. If he took his shirt off, television audiences everywhere would puke at the sight of his scrawny frame with skin on his formerly fat midsection that he would have to tuck into his shorts. Buff my backside...
Anyway, sorry to make this so long, but I hope it will make you think twice about continuing with what I would consider a fad diet that would be impossible to maintain long term.
Biggerisbetter