After sleeping only 3.5 hours a night for three nights, young men reported feeling much hungrier and more tempted to eat, and less full after meals, even when they ate the same food as when they slept longer.

When young men slept less, they burned a little more energy during the night because they were awake longer—but this extra burn didn’t add up to more total energy burned over the whole day.

Even after sleeping only 3.5 hours a night for three nights, young men burned the same total amount of energy and used the same mix of carbs and fats as when they slept 7 hours.