I was skeptical about this at first - just four weeks? But I picked up the book and I gave it a go. I love all of the extra info it provides about why 4 weeks is the perfect length of time to follow their diet plan and I lost 10lbs in the first week! There are five "phases" to follow and they're all really well written and explicit, so you're never taking a blind stab about what to do next. Buy this! It bloody works!