I think what the article is trying to say is, yes, there is a behavioural (psychological) component. But there is also a metabolism (physical) component too tha

I think what the article is trying to say is, yes, there is a behavioural (psychological) component. But there is also a metabolism (physical) component too that is not getting enough attention. (Your own example highlights this well - when you were younger, you could eat more, and / or perhaps lose weight faster too, but now your body's metabolism has changed and you put on weight more easily). For e.g. thyroid imbalances can cause someone to put on weight, and can be addressed medically. The author believes there may be many other similar factors at play behind someone's obesity. I partly agree with the author. But there is another factor - we also know that processed and / or junk foods definitely contributes to obesity. Yet, many obese people refuse to change their diet. If obese feel that they can't do without 1000 calories in their diet, why can't they eat 1000 calories of vegetables instead of 1000 calories of processed food? If gut bacteria plays a huge role in the kind of food we like to eat, then the author has a solid case ...