What do you say when someone comments on the "fattening" food you are eating?

I lost over 65# 3 years ago and have kept it all off. I am 58 and am my gyms spokesperson for 2012 which involves a radio and TV interview, tv ads, newspaper and magazine ads as well as some guest appearances. I have no problem modeling "workout clothes". I have also been asked to model in several fashion shows and some other print ads. (us 58 year olds are the new role model for skin creams and such) I am asked all to often "should you be eating that?, are you off your diet" when I eat something "fattening". Yesterday at Christmas dinner my mom asked that when I had apple pie and ice cream for desert. I am tired of explaining to people (my BF included) that I lost my weight by lifestyle changes, it has been off for over 3 years and obviously my gym thinks I'm great! I'm not good with fast comebacks but would like a "statement" to make when these things are said. I'm tired of telling everyone close that it hurts when they say such things. Any suggestions?