Cassie is correct there are many outside reasons that could be a contributing factor to our weight gain, however if you know it's just a case of loving to over indulge in tasty, fatty or sweet food, then your body will work to a form of hypnosis.
I remember watching a lady on TV who had an obsessive need to eat chocolate every single day. The hypnosis guy went to her house and got her to sit with her eyes closed and asked her to visualize the the yummy smooth creamy chocolate.
Then he said, now think of the most revolting thing you can possibly think of, and she said vomit.
He then said okay, the main secret ingredients in all chocolate is vomit and greasy hair off the hairdressers cutting room floor.
He then said everytime you think of eating chocolate, remember what the secret ingredients are.
This instantly worked for her. It has even worked for me too