I don't know if the same things happen in Norway or not but some overweight people are actually overweight due to some metabolism problems. Their injected fats won't burn off easily. They need to be doing like 30 mins to 1 hour of exercise everyday to prevent from being overweight. That is not easy to do when you become adult and have more works to do, compared to a kid.
Think about this, you're hungry so you eat. Then your fats are still there even when you get hungry again in the next 10 hours. So you have to eat a little at least, otherwise you will have stomache related problems. Yea, it seems makes sense than not eating might make you lose weight but, before that, stomache problem comes. That's hard to deal.