Free will is an illusion. Free will can't even be properly defined except as a negation of determinism, because it doesn't exist. Welcome to the mechanical universe.
Whether one can overcome an addiction or not can be judged in place of our everyday existence where blame is necessary or logically from the perspective of determinism.
I would point out that while obesity is a problem across many different nations, our country's subsidization of corn vs sugar cane promotes obesity. Blaming societal problems on individuals is always a fallacy of simple minds. It's not like people lost self-control. Rich people have been fat since forever. If this quantity and quality of food had existed 300 years ago, the same obesity rate would have existed. In fact, it would be greater since having fat was seen as attractive.