How do you measure body fat vs BMI?
Specific gravity by Archimedes’ Principle. If you were 100% fat, you’d float.
All I can tell you is that my sister and I have nearly the same BMI. She has much more fat than I do, because I can see hers readily, and a lot less stamina. If she’s lucky, she gets in 1500 steps a day. I’m closer to 15,000 steps a day. So this study doesn’t surprise me.
BMI:
https://www.thecalculatorsite.com/articles/health/bmi-formula-for-bmi-calculations.php
All the fat percentage approaches are quite different from each other. The gold standard is underwater weighing, which can get done at most colleges, but a slight electrical charge or even using calipers on various parts of the body, against a set of tables, can provide it.
The simplest is bio-impedence, on a newer scale, adjusted for your height.
These may cost as little as $25 now, on Amazon.
Through a DEXA scan or a Bod Pod.
Our insurance company (at work) does it once a year. they take the reading off your left arm for some reason. It’s a handheld thing that is about the same size as the one nurses use to take temps with. I still lift a lot and do a daily workout. I’m 13% at age 66 and 5’9 169 I’m on the border of overweight by BMI.