Leptin and ghrelin: Hormones that manage your weight
Breus goes on to say that lack of sleep and weight is connected to nightly hormones.
There are two hormones work at night to help your metabolism. One is ghrelin, which is a hormone that tells you to eat when you are sleep-deprived. Sleep deprivation produces more ghrelin in your body, and when you are awake, you eat. Usually what you eat is high in calories and sugars. Leptin is the other hormone and this alerts you to stop eating. When you are sleep deprived, leptin is not produced in your body, so it may not tell you when you should stop eating.
Simply, more ghrelin and less leptin bring on weight gain. Also, when you are sleep deprived, your metabolism is slower, and it is harder to burn calories.