There are also other things they could do that would impact future healthcare costs, like a nationwide ban on vending machines in schools and re-emphasizing the importance of and providing more funding for gym programs.
There's plenty that could be done with food labeling (among tons of other things) that would impact future healthcare costs by directing people towards healthier choices now. For example, I'd like food to be labeled A, B, C, D, or F (and maybe +/-) in addition to the current nutrition label. 100 calorie packs, low fat, and dozens of other labels all sound like they're good for you, but don't reflect things like nutrient density. 0 g of transfat? Must be good! Oh, wait, there's 500 g of saturated fat. Only 100 calories per serving? Wait, there's 30% of your recommended sodium intake. Not so good for you now, is it? I think by making things more explicit and intuitive, you would drive people towards making better choices.
Also, stop subsidizing corn. People would grow less( because the only way they turn a profit now is because of the government subsidies) and the cost of junk food would increase without artificially low corn syrup prices.