A study conducted by the University of Chicago, published in the magazine Annals of Internal Medicineindicates that not getting enough sleep alters hormones which can affect a person’s weight.
University experts involved in the study summarized their findings saying that spending a restless night tossing and turning often has a negative effect on a diet. According to the study, this partial sleep deprivation alters the levels of hormones that regulate hunger and appetite. One hormone, leptin, tells the brain that the body doesn't need any more food, while another hormone, ghrelin, provokes feelings of hunger. 
Research done on 12 healthy male volunteers between the ages of 20 and 25 who slept only four hours a night for two days was conclusive. They experienced an 18% decrease in leptin and a 28% increase in ghrelin levels. The lack of sleep triggered the hormones to send incorrect signals to the brain encouraging it to eat a lot more.
After sleeping only four hours a night, the volunteers in the study had a 24% increase in their appetites, and experienced increased cravings for sweets, such as candy and cookies; salty foods, such as french fries and nuts; and starchy foods, such as bread and pasta. Cravings for fruit, green vegetables, and dairy products didn't increase as much.
The university team also suggested that lack of sleep is one of the factors contributing to the prevalence of overweight and obesity.
Many people in the United States are simply sleeping less. In the last 40 years, developed countries have reduced the average time dedicated to sleeping. In the United States, people sleep two and a half hours less, and at the same time, the number of people who are overweight or obese has increased significantly.
Forty years ago only one out of every four adults was overweight, and one out of every nine was obese. Today, two out of every three adults are overweight, and almost one out of every three is obese.
