Poor sleeping swells concentrations of a hormone that makes you feel hungry while suppressing a companion hormone that otherwise signals food satisfaction. Despite being full, you will still want to eat more. 

And if you try to diet but don’t get enough sleep while doing so, it is futile, since up to 70% of the weight you lose will come from lean body mass, not fat. 

Routinely sleeping less than six hours a night also compromises your immune system, significantly increasing your risk of cancer. 

So much so, that recently the World Health Organization classified any form of night-time shiftwork as a probable carcinogen.