When you sleep less hunger hormone Ghrelin goes up causing you to eat more the next day. When you get more sleep Leptin levels rise so you will be less hungry the next day.

—Subjects that avg. 4 hr. sleep/night:

Leptin went down (18%), Ghrelin went up(28%)  subjects reported hunger (24%) increase in  carb cravings, especially sweets, salty, and starchy high calorie snacks  (Ann Intern Med, 2004, vol. 141, pp. 846—850)

—Out of 1,000 volunteers: those that avg. , 5 hrsleep had leptinlevels (15.5%), ↑ ghrelin (14.9%), ↑ BMI (3.6%).  Results were regardless of the subjects diet and exercise habits. (Mignotet al, Stanford School of Medicine Dec. 2004)