BMI is trivial to measure conclusively, using tools that are almost universally available and ready. And at population scale, it's proven to be a strong and pretty signal for analyzing in studies like these as the ways in which BMI can fail for individuals is too uncommon for it to matter to population studies.
It's a perfect tool to use for studies like these, as it can contribute understanding society-level concerns about the obesity epidemic and what impact we can expect it to have if it continues not to be tackled.
But like with almost all medical and nutritional research, drawing conclusions for yourself as an individual based on these population-scale studies is inevitably fraught. In the case of BMI studies, you can often get a fair sense of whether you should be concerned or not, but do need to take into account other things that you know about your lifestyle and health. Your doctor, presumably, does exactly that.
Meanwhile, body fat percentage tends to be very hard to measure accurately in the first place and has different techniques that tend to have different error characteristics, making it hard to correlate it between studies done through different clinics, let alone against someone's personal assessment at home or with their personal doctor/trainer/whatever. It probably has high relevance to some medical and nutritional outcomes, but isn't a very useful input variable for research because its inescapably noisy.
It's a perfect tool to use for studies like these, as it can contribute understanding society-level concerns about the obesity epidemic and what impact we can expect it to have if it continues not to be tackled.
But like with almost all medical and nutritional research, drawing conclusions for yourself as an individual based on these population-scale studies is inevitably fraught. In the case of BMI studies, you can often get a fair sense of whether you should be concerned or not, but do need to take into account other things that you know about your lifestyle and health. Your doctor, presumably, does exactly that.
Meanwhile, body fat percentage tends to be very hard to measure accurately in the first place and has different techniques that tend to have different error characteristics, making it hard to correlate it between studies done through different clinics, let alone against someone's personal assessment at home or with their personal doctor/trainer/whatever. It probably has high relevance to some medical and nutritional outcomes, but isn't a very useful input variable for research because its inescapably noisy.