No, the reason people are fat is diet and lack of physical activity, they just don’t want to give up their lifestyle. Nothing changes “calories in vs calories out”. Saying it is “glandular” and such is a way of defending your drug of choice, food. If you keep a food diary you quickly realize how many more calories you are eating than you admit. Now changing that is tough because every fiber in your being is fighting you and it requires a multipronged approach. I know people who have lost weight and kept it off through diet and changing their attitude towards food (i.e. not treating it like a reward).
BMI is sketchy and at the boundary points doesn’t take build into account. Still, at large BMIs it does reflect a general fat burden.