@TheDragonLord
A
far larger proportion of incorrect BMIs are false negatives (normal BMI, overweight/obese composition) than false positives (obese/overweight BMI, normal composition):
People with an obese bmi and an athletic build are nearly a
rounding error as a percentage of the population.
Edit: Changing image file to a URL, it came out way too large on the page -> http://i.imgur.com/vqoyBGj.png
Sub-18 BMI is a scary place, but that's just BMI. If you wanna get specific, from a fat % point of view, under 6% is the scary place where organs can fail. 10-12% is fine, though. Most people are 25+%.