Originally Posted by Aftershock

You can be fat and fit, fat is just a surplus calories taken in over a period of time, that remain because you haven't been in a calorie deficit to burn them off.

You can be overweight, exercise and get fitter but still take in surplus calories and you will stay fat.

There are some athletes "cold water swimmers" for example who have higher bodyfat levels but are still very aerobically conditioned.

All that said the majority of the population who got fat did so because they ate crap and didn't do any exercise, so you wouldn't expect these people to be fit.