Would a Soda Tax Lead to "Vitamin Fortified Soda"?

In general, food (other than restaurant food and prepared food) is not taxed. Presumably, this is because it is seen as more of a necessity than other goods. There is discussion of a variety of possible taxes on foods that are thought to contribute to obesity. A FB friend pointed me to two articles about a possible soda tax when I commented that I will be teaching a course on the economics of obesity (http://online.wsj.com/article/SB124208505896608647.html and
http://blog.indecisionforever.com/2009/05/14/colbert-announces-coke-party-protest/).

I would think that of all the food taxes that we might (and I say carefully--MIGHT) get people to agree on, a tax on soda--specifically sugared soda--may be considered most reasonable. However, I think there might be an unintended consequence--vitamin fortified soda in our collective future. Let's consider a few alternatives.

First, let us consider taxing all soda rather than taxing only sugared soda. While sodas sweetened with sugar substitutes have few or no calories, some people worry about the health effects of the sugar substitutes. However, I recently heard someone comment that while the substitutes may cause cancer because of their chemical properties, enough sugar can contribute to the risk for cancer as well. Enough sugared soda will increase the risk of becoming overweight and this can contribute to cancer. So, we might argue that all sodas should be taxed, but taxing only sugared sodas seems reasonable since it creates a whole series of risks (including cancer) that are related to being overweight.

Second, we could tax other high calorie foods. However, it could be argued that many have at least some redeeming qualities. Chocolate with nuts has the nutrition of nuts. Juices have lots of natural sugars and lots of calories but also have the nutrition of the fruit (or vegetables) from which they are made. Even sugared cereals could be argued to be fortified.

If a policy maker were to make the last argument, he would implicitly be suggesting that any tax would not be based on only caloric content but would be determined through some process recognizing a tradeoff between calories and nutrition. This might allow for producers of sodas to avoid having their goods taxed--by figuring out how to produce vitamin fortified sodas.

Wouldn't that be an interested unintended consequence of a soda tax?

Of course, this is all strictly hypothetical and there is absolutely no guarantee that a soda tax could be successful in politics when there are powerful interests who would argue heavily against such a tax.