I have EFS and the Four Day Diet, and the biggest difference I see is that the FDD is a little more flexible. I only made it through two weeks of EFS before I couldn't take anymore brown rice and beans! The FDD is broken up into 4 day modules, so when you get bored or frustrated (haven't been either yet), it's time to move on to the next module. I've done it for two weeks now, and I don't feel deprived or frustrated. I like it so far!