Lack of sleep causes a hormone called cortisol, which controls the appetite, to take excess calories and store them as excess body fat. In addition, sleep loss interferes with carbohydrate metabolism which may cause high blood glucose levels. The excess amount of glucose encourages the overproduction of insulin, which may lead to diabetes or even obesity.
These calories are not so easily shed than taken. When they are sleep deprived, people are often too tired to exercise or they work out less intensely than usual. They commonly feel exhausted and lack the energy and motivation to do even simple exercises. They rather go to sleep, or eat, than go physical. In due time, the calories that are gained and not easily burned are deposited in the body as fat. But you need to work and you will sleep less every day!
