I doubt that someone with a BMI of 48 is "healthy".
Well tell me how I'm unhealthy, then. The number is an arbitrary statistical tool, and was never intended for diagnosis. Health depends on the individual's actual medical status. I'm on no medications whatsoever, I'm in no pain to speak of other than periodic muscle aches after workouts. I have no difficulty breathing. My BP and heart rate are higher than I'd like but not particularly dangerous, and they're steadily decreasing. I get regular checkups. I'm not as quick as a smaller person, but then again I could pick that small person up and break him, or just kick his knee backwards.
So really the only problem is the extra fat, but fat per se does not make you unhealthy. It has been associated with medical problems, but the studies to date have done a poor job differentiating between medical problems caused by fat per se and those caused by inactivity and bad diets. Moreover a study is looking at patterns, it says nothing about any particular person. The biggest direct problem appears to be pressure on the joints, and that's the main reason I'm losing the extra pounds. Also because of my left knee injury, which is mainly what caused me to put on weight in the first place.
I'm not disputing that I need to lose weight. I'm saying that I am healthy now even though according to the BMI number I'm "morbidly obese." You would never look at me and call me thin. I'm a mountain with enormous leg muscles. But nobody would see me and think "gosh he's about to die from his fat." Nor would they ever imagine how much I actually weigh. I'm not a person who develops a beer belly. My fat is evenly distributed. None of this is taken into account on the BMI, which is why it's utterly useless as anything but an arbitrary statistical tool.