The most recent Top Chef Masters on Bravo was a vegan, soy free gluten free meal for Zooey Deschanel (sp?). Pretty cool, none of it was what I would have made (maitake) but still good to see it prominently.
Food Network will never do it as a show though. They feel it to be too preachy, anything healthy, they have meat-based and/or unhealthy sponsorships they would be afraid to offend. They also don't want their viewers to think too much nor beak out of a dietary mold that would challenge them to be better.