I grew up with a mom who was OCD about her weight and fitness, I'm not exaggerating, she actually had OCD and it came out through cleaning and exercising/being obsessed with what she ate. She used to make my 'chubby' older sister exercise and diet, that sister is now obese/morbidly obese. She never 'did' anything to me since I was naturally small but obviously watching her obsession with her weight and growing up with such a 'perfect' mom in terms of body image rubbed off on me in not positive ways. Imagine what mine or my sister's attitude towards our weights would be if body image had been viewed differently in my house.
She now has an under active thyroid and although she no longer has OCD in terms of food or exercise she still eats healthy and is active but is 'chubby' because her thyroid won't allow her to loose weight. I have friends with PCOS that can't loose weight no matter how hard they try and other friends that put on weight due to antidepressants. Both situations that are out of their hands, they can try and be as healthy as they want but the weight just isn't going to drop. I would gather that some with the attitude that they may be overweight but are healthy find themselves in these situations where they genuinely can't loose weight due to other medical issues.