If you don’t get enough sleep for 8 days, your hunger hormones don’t change much—so if you end up eating more, it’s probably not because these hormones are telling you to.

When adults between 30 and 60 don’t get enough sleep over a long time, their body makes less of a hormone that tells them they’re full; but if they miss a night of sleep, their body makes more of a hormone that makes them feel hungry—so different kinds of sleep loss affect hunger in different ways.

People who sleep only 5 hours a night tend to have lower levels of a hormone that tells your brain you're full, compared to those who sleep 8 hours — even if they're the same weight or age — which might make them feel hungrier.

If you only sleep 5 hours instead of 8, your body might produce more of a hormone that makes you feel hungrier — even if you’re the same weight, age, or sex as someone who sleeps longer.

When people don’t get enough sleep for eight days, they don’t end up moving more to burn off the extra calories they eat—so they’re likely to gain weight just from eating more, not from being lazy.

If you cut your sleep down to just two-thirds of what you normally get for eight days straight, you’ll likely eat about 559 extra calories a day without moving more—this could be why people who don’t sleep enough tend to gain weight.