So raise it on a small minority of the population?
I have a better idea - raise the tax on bread, and all the ingredients needed to to make it an equivalent amount, thus equally taxing everyone.
That's it...a carbohydrate tax (what's your carbo-footprint) If you want to decrease a behavior, tax it. So tax fat people...and smokers.
The non-smoking Atkins diet people get off Scott-free.