Many studies in the past have shown a strong relationship between sleeping and staying thin. People who don’t get enough sleep have a tough time staying skinny. Well now, researchers from the University of Chicago have figured out the reason why.

An article on BusinessInsider.com explains that people who sleep fewer hours each night have higher levels of a molecule which stimulates appetite. In other words, being tired makes you hungry – which ends up making you fat.

The molecule is similar to chemicals in marijuana, which gives users the "munchies" making them want to eat more.