Sometimes I try to pass it off by joking a bit, "Oh, I'm on a health kick right now" or say I've decided to avoid processed foods / sugar / white flour, etc. That way it sounds like more of a health decision than a weight loss thing, and people are generally more accepting of that.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days