The following is an answer and/or comment by inhahe aka ColorStorm (inhahe.com - myriachromat.wordpress.com).
Yes, for two reasons.

1. If people don't have the motivation to learn enough about health to want to eat healthily, or don't have the will-power, then they need a government-as-parent to make their decisions for them. Why? Because when you're healthy you're happier. I think people underestimate how big a role physiology plays in one's well-being, and how big a role eating healthily plays in physiology. So therefore even if it means being like a nanny state in this regard it's for the people's own good. It's the same basic reason we don't allow people to buy cocaine, or to buy food products from companies that would kill you the next day, just on a subtler place in the continuum.
2. Everyone should have the right to health care, and under universal health care those people who actually eat and live healthily end up paying more in order to compensate for those slobs who eat whatever they want all day, and that's not fair. It's not fair to have to pay for others' negligence. Even if you don't believe everyone has or should have the right to health care, this principle applies to anyone who pays for insurance too.

I don't really think the government should put you in jail for having an unhealthy lifestyle, and I'm not even sure they should fine you for it, but our foods should be more heavily regulated somehow. Like, there should be a lot less junk food and unhealthy ingredients on the shelves and on the menus. Maybe you should be able to splurge and eat something unhealthy but really delicious once in a while, but there should be some kind of accountability for how often you do this.