Medifast is soy-based, so if you are allergic, it is not the program for you.
MissyGith is using a Medifast alternative that is whey-based, I believe. I can't recall the name of her program, but it is very similar to Medifast (and cheaper!). If you look through her old posts, I'm sure you will be able to find the name of her program.
Total Weight Loss (HW 5/2010)
Post WLS (8/1/2011)