Honestly, anyone who would talk smack about the food you are eating WHILE you are eating it deserves nothing but ridicule.
Unfortunately, I have an anger issue myself which I not very proud of, but I honestly think that some things require standing up to people and anyone who is talking crap about your food is asking for it. Thankfully, in the one time I have had where someone giving me a hard time about food at work escalated, the guy (who I ended up tapping on a couple of times after a nasty verbal exchange) decided to keep his mouth shut with HR since he didn't want to have to explain to management why he was incessantly haranguing me about the food i was eating.
Anyone who mocks or insults your disorder deserves whatever you are capable of dishing out to them. There is no excuse for it and anyone who feels the need to attack another person about something so personal knows exactly what they are getting into but have such disdain for you that they don't fear any retribution from you.
As the old saying goes: "If they didn't want to win painful prizes, they shouldn't have played that kind of game."