Not getting enough sleep could be one of the main reasons more and more kids are becoming overweight.
An expert in obesity reckons kids are staying up later playing computer games and watching TV in their rooms.
But he says a lack of sleep makes you want to eat sugary food to give you energy - and that piles on the weight.
Not getting enough kip also makes you tired, meaning you're less likely to want to do the exercise which would keep your weight down.
Dr Shahrad Taheri said the chemicals our bodies make to control things like how hungry we feel are affected by how much we sleep.
He reckons one of the first steps towards fighting the problem is taking gadgets out of your bedroom to encourage you to get your head down.