I beg to differ, of course diet and exercise strategies are key to attaining and maintaining a healthy weight. The only way a person will lose weight is if they take in less calories than needed. Not many people know how to cook appropriately too and will make/buy too big or too rich meals out of habit. More often people fall back to their old habits when things are beginning to look well (like those shitty tabloid 7-day diets, in the end they changed nothing), they need therapy to drop those instead of surgery.

If you can't drop (basically any) bad habits, please look into getting behavioral therapy.