People will not quit on their own. Tobacco usage has been dramatically reduced through a combination of the following strategies:
1. High taxes. Tobacco used to be ridiculously cheap, now it is essentially a luxury good. Sugared foods are likewise very cheap. Add a tax of 200% and I can guarantee you people would think twice before buying a $15 (previously $5) pack of Oreos. Of course people will bitch, but they're stupid and don't know what's good for them.
2. Limited package and portion sizes, and bans on discount pricing. While not all jurisdictions have implemented this, some places don't allow for savings when you buy a carton as opposed to a pack. It has to be as inconvenient as possible to indulge the habit.
3. Banning vending machines (especially drinks, but also snacks). Recall that there used to be cigarette vending machines.
4. Banning all forms of advertisement.
5. Many (smart) countries ban package branding of any kind, requiring plain font on solid colored packaging. There is no reason this could not be done with cookies, cakes, chips, drinks, etc.
6. Prominent warning labels. "SURGEON GENERAL'S WARNING: This food product is dangerous to your health and will reduce your lifespan if habitually consumed." "SURGEON GENERAL'S WARNING: This product is known to cause diabetes, heart disease, obesity, and early death." etc etc
7. Publicly funded advertisements, particularly targeted to children and young adults who have not yet become fully habituated to garbage food.
This will happen sometime in the next 100 years, but probably not before ~50% of the population is obese and ~70% is overweight. The food industry, like the tobacco industry, has used a militant disinformation campaign to ensure that it does not happen.