In our culture today, we tend to be chronically sleep deprived, as we strive to fit more into our daily routine. A common theme when we talk to someone is that they're so busy, and there's just not enough time to get everything done. People are stressed, and don't get to bed early enough, and when they do, they can't get to sleep, or stay asleep.
So, how does lack of sleep affect your weight? Research has shown that chronic lack of sleep increases the levels of a hormone - ghrelin - that signals your brain that you need to eat...you feel hungry. At the same time another hormone - leptin - that sends a signal to your brain to tell you that you are full decreases, causing you to eat more.
Also, when you are tired you become less active, and when your energy is low, you will be more likely to reach for sugar rich foods in order to boost your energy. Thus starts a chain reaction of lack of activity, eating to much, and eating foods that are high in sugar, and fat.
When you are overweight, you increase your risk of developing chronic diseases such as heart disease, type 2 diabetes, cancer, etc.
Research has found that people who get 4 hours or less of sleep a night are 73% more likely to be obeses than those who get eight or nine hours sleep a night.