Matthew Walker of the University of California, Berkeley, measured people's food choices and imaged their brain activity after a night's sleep and after a night with no sleep.
The study, published in the journal Nature Communications, found people preferred fast food after the sleepless night, and their sleep-deprived brains showed less capacity "to make good-for-you choices and more I-wanna choices."
"There's a shift in the behavioral choices that people are making, and that seems to be co-occurring with those changes in brain activity."
Those who get enough sleep might make better food choices and eat more healthfully.
Studies show some adults might need 7 hours a night, while others may need 9 hours to have a happy, productive life, but it's recommended all children and teens get 9 hours of sleep a night.