Erin Hanlon of the University of Chicago said the study involved nine people who spent 13 nights in a sleep lab, gave blood for analysis and ate a controlled number of calories.
Hanlon examined the chemical 2-AG, which is part of a system that has a role in enjoyment, such as enjoying eating. She said when people were allowed fewer minutes of sleep, their levels of 2-AG were higher in mid-afternoon -- just in time for the mid-afternoon snack.
"Individuals need to think of adequate sleep as an important aspect of maintaining good health, and not just as a by-product of the day," Hanlon said in a statement.
The study was presented at a meeting of The Endocrine Society.