I'm about 6'2 and very lanky. My problem has always been that I don't eat enough, and my doctors have told me all my life I need to consciously try to eat more

I'm about 6'2 and very lanky. My problem has always been that I don't eat enough, and my doctors have told me all my life I need to consciously try to eat more (which I try to do) to gain weight. I don't really do any planned exercise but I don't have a car so I get some daily workout from walking/cycling. In short, I'm no fitness nut or bodybuilder. Every time I've taken BMI, the result is that I'm "slightly overweight". That's bullshit. If I actually tried to eat less, I'd probably end up having health complications related to malnutrition. So BMI is very much bullshit when applied to individuals. It might have some relevance for the average case, and therefore be useful for demographic comparisons of large groups.