Because the bathroom scale is always just sitting there, and I am a curious person, I weigh myself before going to bed, and then again in the morning. I find that I lose about 1% of my body weight by sleeping. If one third of my day is spent sleeping, and I want to lose 20 pounds, it would seem that the easiest way to do so would be to sleep for three days straight.
Eve Van Cauter has been studying sleep for a long time. While I am sure she would not recommend my sleep diet as a weight loss method, she has found that sleep regulates the levels of hormones that control appetite, and that not getting enough sleep makes people hungry.
In December of 2004, she published a study of 12 healthy young men, where she found that levels of the hunger causing hormone ghrelin increased, and levels of the hunger preventing hormone leptin decreased. The appetites of the men increased when they were allowed only 4 hours of sleep, and they especially craved calorie dense foods high in carbohydrates. When allowed 10 hours of sleep, their appetites returned to normal.
Leptin is reduced by the hormone melatonin during the night. Light prevents melatonin from being produced in the body. Artificial lighting at night reduces the amount of time that melatonin is produced, and this can reduce the leptin levels, causing hunger and cravings.
Leptin is produced in the fat cells, and tells the body how much energy is stored away. It not only regulates hunger, but it regulates the metabolism that burns energy. Low levels of leptin are associated with obesity.
It may be the beauty sleep that keeps you thin, or it may just be that you need more than 4 hours in the dark to produce enough melatonin to keep the leptin levels down. The exact number of hours of sleep (in the dark) that you need is probably higher than the 4 hours used in the study. Other studies have shown that sleep is necessary for memory, and suggest that at least 7 hours is required for full function.
Turn out the lights, and get to sleep.