That's a great idea, but one that will never in a million years be entertained by our government.
Lets look at the bedroom tax for example. The less fortunate got hammered for extra bedrooms in council housing which they were allocated. The government received nothing but negative press for this, and instead of abolishing it - they introduced mansion tax to balance the scales...
The route they chose to make things "even" for everybody, ultimately resulted in them being quids in. I'm afraid the same applies for removing or reducing tax on healthy foods... It's not an option the government will contemplate because they can make more money taxing the unhealthy stuff. Real shame.