I travel cross country twice a month, and I've been compiling notes on airline food and LC travel tips. One of these days I'll get around to writing the article I promised myself I'd do as a result of all that I've found.
In a nutshell--it depends upon the carrier. I usually fly on Alaska Airlines, and the diabetic meal has been the best option there. American Airlines didn't do well with either diabetic or gluten free. In fact, the gluten free breakfast was a rice cake, banana, and non-fat fruit (and sugar sweetened!) yogurt--almost 100g for one meal!
Northwest Airlines had a pretty good choice with the dairy-free lunch, but there was still the granola bar to avoid.
In all, until the airlines come around the best you can do is pick out what works for your WOE, and pack plenty of portable LC snacks to round it out. I always have with me a couple bars or a snack-size ziplock with almonds, or a couple of those tiny wax-covered cheeses.
And water. Take a liter bottle with you, and don't be afraid to ask for more than one of those teeny cups full when the beverage cart comes by. The air flow in an airplane cabin is so dry you can almost feel your skin crack.
One last thing: I take every opportunity to tell the carriers that LC is an option! Ask for it when you make your reservation. Call the carrier and talk to customer service. Send it in with the customer comment form on the carrier website. Anything to let them know there is demand for it. That's how all those other options got in there--if they figure the paying passengers want it, they'll think about it.