How does it work? I read in amagazine about someone who was a size 22 at 15 stone, and I weigh more than that and I'm a size 18 on the bottom and 14 on the top. I don't look that fat, but my BMI suggests I am.
It depends on how much fat a person has on their body. Muscle weighs more than fat, so they may have had more fat than muscle... But I don't know the scientific reasons....
If your BMI is over 25 then yes, thats an indication that your overweight but dont rely on it. However, get your body fat tested and lean muscle percentage done and if your body fat is more than about 25% it might help to reduce it.
More lean tissue the better normally but not sure of good proportions.