[rsheridan6]

That's not practical. The government would have to keep track of your health and communicate it with every retailer.

[yummyfajitas]

They could also just give you a fitness test once a year at the IRS office and tack your unhealthy choices onto income taxes.

For the middle class, this would be more optimal than taxing soda, since it rewards the outputs rather than the inputs. For the poor (who mostly don't pay taxes anyway), this wouldn't work so effectively.