It’s really not a good metric. It’s incredibly noisy. “Are you fat” isn’t something that needs a noisy metric. And it makes analyses messy when bmi is used as a measure of fatness.
I knew a guy who really wanted to join the fire service but couldn't meet the BMI requirements as he was in the 'obese' BMI bucket, In this case he was just very broad and very muscular (built like the colloquial brick shithouse). By their requirements jonah lomu would not have been able to join because he was 'obese'
If you’re not working out and fat, BMI is still not a good descriptor of “how fat” or “how consequentially fat”.
And yet you’ll still get scientists mapping out correlations and then it’s a shitty analysis because it does not show what the study assumes.