I think of it like this. I’ll make an exception for people who have BMI in Obesity Class II and up - they are relatively rare, and it’s true that most have very high body fat.
But take 5 normal Americans with BMIs of 16, 20, 23, 26, and 33. It’s a fairly safe assumption that the three with the lowest BMI have less body fat than the ‘obese’ person, but that’s all I think is reasonable to infer. The following examples are all based on people I have known.
The person with a BMI of 16 could have a small frame, be completely sendentary, have very little muscle mass, a normal fat percentage, and eat large amounts of junk food (this was me until a couple years ago) - she needs to eat plenty of protein, exercise, and mostly needs to build muscle.
The girl with a healthy and slim BMI of 20 could be struggling with severe anorexia and bulimia - she needs to stop starving/binging/purging/overexercising and putting such a strain on her body that she is fainting regularly, her teeth are being damaged, she is at risk of organ failure and heart problems, and hasn’t had a period in 4 years (this was my good friend in high school). Turns out her body fat is quite low, she gains about 15 lbs much-needed pounds after her recovery.
The person with BMI 23 could be an inactive person who eats whatever he wants without getting fat, but he has a relatively high body fat percentage and a beer belly - he needs to eat better, exercise, build muscle, and lose at least 5% of his body fat for his health’s sake (see many of the nerdy men I know).
The person with BMI 26 could be a competative cyclist with an ‘athletic’ body fat percentage - she doesn’t need to lose any weight at all, if she does some of it will be muscle (another friend of mine - she has a sturdy frame and large muscular legs).
And let’s say the person with the BMI of 33 is your typical obese person (IMO) who used to be slimmer but doesn’t exercise very regularly and eats plenty, therefore has seen a steady weight gain over the years and has a high body fat percentage. He needs to exercise more, eat less and maybe better food, and lose quite a bit of body fat. However, he is 6’4" with arms like a lumberjack, and during the years he played college basketball when he was young, very fit and lean he never had a BMI of less than 27, so while he knows he needs to lose weight he rightly thinks his doctor’s insistance that he should lose weight until his BMI is less than 25 is impossible, even if he was able to play ball for 5 hours a day again (this is my boss). His body fat percentage is what he should be aiming to reduce, and once it’s in a healthy range it doesn’t matter what his total weight is.
All of these people should receive completely different medical advice, but calculating their BMI doesn’t tell their doctors what it should be. This is why I think BMI is pretty useless for most people.
), but I’d be more likely to be described as “athletic” or “solid” than overweight, for sure.