My response is simple.

I tell them I am diabetic and my doctor has decided that in order to stay off insulin I must stick to a diet that has no sugar, potatoes or bread in it. Then I just smile. Most people don't bother with a retort they just nod and keep going.

That is, until I start eating the pork skins and hot sauce. I just remind them that I can have them in place of the bag of potato chips they're munching on, and point out how much carbs-to-sugar danger there is in that little bag they're holding! Shuts 'em up every time.

Besides, most of the folks around me are dieting, too, and they're looking at my lunch every day quite enviously!

T