It’s been know that people who don’t get enough sleep tend to gain weight. One possible mechanism is due to high ghrelin and low leptin levels.

But another probable mechanism is due to the endocannabinoid 2-arachidonoylglycerol (2-AG), which essentially gives you the munchies.

Lack of sleep alters brain chemicals to bring on cannabis-style ‘munchies’ • Neuroscience • 2016 Feb 29 • Ian Sample • The Guardian