Well, if you can mandate you purchase insurance, why not mandate you have to buy lunch. Hell, tie the systems together, so that what you buy for lunch immediately impacts your insurance premium, and whatever the status of your health mandates what you can purchase for meals, too. Depending on if they want you to live (liberal) or die (conservative).
1) Obamacare says they're not allowed to risk-adjust rates, which is why the premiums are skyrocketing.
2) I'm sure they'd try that, but most "nutrition science" is so fsked up the law of unintended would definitely kick in. They'd end up killing all the libs and the normal would still be alive. Oh, wait......I'm rethinking my position on this.....