While I generally agree that heaping stigma onto people with undesirable behaviors is ineffective, I'm not sure it is even relevant in the case of changing our overweight/obesity prevalence. Comparing it to smoking is not accurate, either.

Asking whether stigma would be a useful pressure in getting people to change their weight presumes that we have good solutions for people to embark upon once they decide to make a change. The reality is that many factors act against a person trying to lose significant amounts of weight, including metabolic factors, and the very real inability to calorie restrict and cope with hunger/undereating for an extended period of time. This is one reason why the smoking comparison is inappropriate--smoking is a chemical addiction, and while it is extremely difficult to quit, smokers can experience less physical craving as they have more quit time under their belts. An overweight person who is calorie restricting will likely experience diminishing returns as time goes on, as well as fatigue from the experience of going hungry often--this tends to get worse with time.

Until there is a productive and reliable method for weight loss, I suggest you put the paternalistic and oversimplified question to bed of how to properly motivate those poor overweight people whom you must be assuming are simply not taking advantage of great remedies for their woeful situation. Please.