Are soda and candy food? Taxachusetts wonders

Massachusetts Governor Deval Patrick has proposed raising revenue and combating obesity by ceasing to call soda and candy "foods." That would mean they would be subject to the state sales tax, unlike other food items.
Somewhat to my surprise I like this idea.
While I support a large social role for government, I sympathize with low-tax libertarians who are skeptical of excessive regulation. But this tax action seems like just the right direction for government. It isn't banning soda. It's just sending an economic message to consumers that they might want to consider alternatives.
This is a good thing, because the state will never be able to persuade consumers about the hazards of sweetened foods. Advertising by Coke, Pepsi and Hershey's will always overwhelm any anti-obesity message.
However, if this is really about combating obesity, the tax should only apply to sugar-sweetened soda and candy -- not sugar-free alternatives. In fact, I think the state should levy a specific tax -- maybe ten cents per can or candy bar -- on sugar- sweetened soda and candy. Consumers who saw that kind of price differential might well switch to sugar-free gum and diet soda.
The sugar tax should also apply in restaurants and fast-food joints. I bet McDonalds would have more than one flavor of diet soda available if sugared drinks all cost 20 cents more. Gov. Patrick's proposal won't impact fast food sales, since they're already subject to the restaurant tax.
If the sugar tax works, maybe the state could go after other insidious food threats that consumers aren't aware of. I'm thinking of white bread and rolls. If they cost more than whole wheat, rather than less (white bread doesn't spoil as fast, so it's cheaper for restaurants and markets to stock) consumers would gravitate to healthier bread. Who knows? Maybe a whole-wheat roll would even mitigate the health horrors of a Fenway Park hot dog.