The average adult needs seven to nine hours of sleep a night. When we get less than this, hormone changes occur that increase our susceptibility to obesity. According to a 2013 Gallup poll, 40 percent of Americans are not getting the recommended amount of sleep. Studies estimate that a third of American adults age 30 to 64, are getting even less than six hours a night, and the lower the amount of sleep, the higher the correlation with obesity. Sleeping less than seven hours a night, raises the level of the hunger hormone ghrelin. It also lowers the amount of the satiety hormone leptin. As a result, our brains get the message that we are hungrier than we should be. Without realizing it, we consume more calories than needed to compensate for the extra hours of being awake. In one study, participants were allowed to sleep ten hours for two nights, and were then sleep deprived with only four hours of sleep for two night's. Following sleep deprivation, their ghrelin level increased by 28 percent, leptin decreased by 18 percent, hunger level increased 24 percent, and appetite for high carbohydrate foods increased 39 percent. Then there's cortisol. Naturally, our level of cortisol is highest in the early morning, and decreases throughout the day. With inadequate sleep, cortisol levels spike again in the afternoon. Just as under stress we crave quick energy carbs, with insufficient sleep, levels of insulin also increase after meals. Higher insulin causes us to store more fat. Therefore, the hormone changes that occur after a poor night sleep, not only make us hungrier and crave more junk food, they also cause us to accumulate more fat. So, what is the sweet spot for the amount of sleep we should get for controlling our weight? People with the lowest body mass index are the ones who get seven to eight hours of sleep per night. Both the quantity as well as quality of sleep are essential. If you aren't getting this amount, there are habits and techniques you can use to train your mind and body, to get a better night's sleep.