I am technically 'obese'. However, I have a very low blood pressure and cholesterol readings, eat healthily and do a reasonable amount of exercise (a decent work out 2 or 3 times a week, I'm on my feet most of the day). So my doctor describes me as 'healthily overweight'. To lose weight I have to pretty much stop eating, and work out excessively. I last between a few days and a couple of weeks, then I start getting constant headaches and every bug going. If I persevere more than that I just stop losing weight.
Basically, my body just holds onto calories very effectively. I'm also hypo thyroid, and have had symptoms since the age of 14, but it took until I was 42 to be diagnosed and given the right meds.
So - even though my weight is 'unhealthy' I am actually healthier being heavy than when I was in my 20s and just didn't eat and was ill all the time.
This idea of there being 'healthy' norm which everyone should fit into just doesn't work. There are people who would have to massively overeat in order to be heavy enough, and others who have to really damage their bodies by denying themselves food.
We really should think more about a healthy lifestyle - food, exercise, relaxation, sleep etc and let our bodies sort themselves out. We don't go on special diets to change height, eye/hair color, but for some reason there is this idea that weight is entirely within the control of the person, whereas genetics is far more influential, with lifestyle playing a secondary role. But then there is a LOT of money to be made to convince people that they should 'do something' to fundamentally change their body type.