eat normally otherwise) worked better for me. Lately I've been doing a 3 day fast once a month, and have been steadily losing weight on that. I need to go for a while longer before I declare victory on that, but so far, so good.

My situation was that if I eat until I was not hungry, I would consistently gain weight (about 2 lbs per month). It was very frustrating. When I got to a point that my weight was unacceptable to me, I would do a very low calorie diet to drop 15-20 lbs. But no matter what I tried, the weight would just creep back up until I knocked it down again. That's not how it's supposed to work.

The 16/8 diet wasn't enough to really change that, but the 5/2 diet at least let me hold my weight constant. It took the addition of the longer fasts to turn things around and start losing weight. Now I have been losing about 2 lbs per month. I want to lose another 10 lbs, so I'm hoping this keeps working. The nice thing is that I am not losing any muscle as far as I can tell--just fat.

The calorie deficit is necessary to lose weight, but according to everything I've read, the power of fasting is that it helps you reset your insulin levels. Consistently high insulin (caused by being in a fed state for most of the day, and also by eating lots of sugar and other refined carbohydrates) makes it very hard to burn fat and very easy to store fat. Fasting causes your insulin to drop, which makes it much easier to access the fat stored in your body.