While metabolism does generally slow down with fasting (it takes energy, ie calories, to digest food), it is a myth that it stays down once you begin eating again! In other words, your metabolism will be slower without food but will return to normal with the re-introduction of food. It is also true that you will gain some of the weight back once you eat again, but this is mostly water weight and the actual weight of food that is in your digestive tract. I hope this helps clear some things up; remember that the benefits of fasting go WAY beyond weight loss. A better recommendation is to not use starvation as a means of healthy weight loss. Fasting is a whole different story and very beneficial.