Eat nothing but protein for a spell, removing all vegetables, carbohydrates etc. Then reintroduce vegetables/fruit after a while. I believe that's it in a nutshell.
I worry about the health effects of it, but it certainly does work and quite quickly (something to do with water retention...) A colleague of mine had a go at it, lost 2 stone but complained of feeling constantly tired. He was actually signed off work ill for a while with heart issues shortly after.