Mindfulness is awareness of what is happening in the present moment, including awareness of thoughts, without any attachment to whatever you notice. Mindfulness is helpful because it creates space between thoughts and actions.
Unfortunately, obesity is not meant to be tucked neatly into a compartmentalized box. It's not as easy as "eat less and exercise more." The cravings come from somewhere and there are reasons why they exist.
Emotional eaters don't want to face unpleasantness in their lives. They don't want to feel any negative feelings. So they eat to get a pleasurable distraction from the feelings, to numb themselves.