Please, if calories in > calories out, you gain weight. Yes, some people require more effort to burn calories, but you can’t tell me that even with a “clinical reason” if you ate nothing but salad, you’d get obese!

Yes many people are fat because they eat too much – or more likely exercise too little.

People with psychiatric ‘conditions’ such as alcoholism or depression can tend towards obesity as overindulging in food and/or drink goes hand in hand with their ‘clinical’ condition – good luck to the airline that starts discriminating against ‘valued’ customers who happen to have psychological disorders.