Most of us know someone who's overweight but just doesn't seem to want to do anything about it. They may even say they're happy being the size they are. So why should that bother anyone?
In tests, experts asked more than 2,000 people with a body mass index of 30 or more - the official measurement of obesity - to look at pictures of different body types from very thin to very obese. Each volunteer had to pick which body type they thought was their ideal. If they picked one that was the same or bigger than their own, the researchers classed them as having body size misperception.
The results showed 8 even thought they had a low risk of becoming obese - despite the fact they already were.
If you think that's surprising, half of the 8% thought they were healthier than most people their age. Many also said they felt they had a low risk of having a heart attack or developing high blood pressure or diabetes.
So are some overweight people in denial? Or should we lay off them - after all, isn't it better to be fat and happy than fat and miserable all the time?