That’s funny. I’ve always been in excellent shape and have thought that the BMI is a terrible indicator. Particularly when my percentage of body fat was very low but I was bulked up from martial arts and rowing. I’ve never been as heavy as I was then, but had remarkably little body fat.
(Ah, to be in my 20s again!)
BMI is not a good indicator because all it considers is height and weight, without considering body composition (muscle vs fat) or frame size. My sister, who is a fitness instructor, was considered “obese” by BMI – and before you conjure up images of steroid-riddled female bodybuilders, no, she wasn’t like that, either. If you weight train, it is simply not accurate for you.
A far better method is determining body fat percentage, but even that has its perils in measuring with precision. Tracked over time, though, it’s a far better way than using BMI.
Also, note that a 2005 study determined that, based on BMI, ‘overweight’ persons had a lower risk of death.