This is done because it perceives that there would be an impending famine and it's done with the intent to protect the body from starvation. So the more you cut down on calorie intake, the more your body would respond accordingly and start to slow down the fat burning ability.

Now, as soon as you start to eat again, your body says hey, food, I don't know how much more I'm going to get so better store as much as I can while I can. The result.