SF has alot of 'added' sugars per shake, this mounts up, should try to avoid sugars which arent natural (like fruit sugars are) having to many of these added sugars can cause you to gain weight, if you dont do enough exercise to burn off th...e extra sugar you take in, it then stores as fat.
Another downside is, SF can workout to be very low calories plan, if you exercise alot, but dont meet min of 1200 calories a day your not making it any easier on yourself, after few weeks of good losses it can easily change around and can start gaining, its very important you drink plenty of water, last thing its lacks alot of protein.
Good luck on it but please be careful on it also