It's called "the Fast diet" or the "5:2 fast diet". It works on the principle that in the wild in nature your metabolism speeds up for the first couple days you go on low food, to help you find more food. (After that you hit starvation mode and lock down on the fat.) But if you rotate calories and have a couple low calorie days, a few very reasonable days and maybe one "free" day where you eat fairly normally the pounds start falling even if they've been stuck on