I had the same thing happen at Easter Dinner - everybody was wondering why I didn't eat and I just said I'm getting over a cold and decided to fast for a few days before I went onto a raw food diet - they didn't need to know how many days I was already on it or how many more days I'm going to do it and the one who was the least receptive to it was my husband's nephew's wife, who used to be 100% vegetarian and the right size for her body, who was convinced that eating meats, etc. was "good" for her and she was "missing out" and now she's a junk food junkie and over 100# overweight in 2 years of eating very badly and no exercise at all.
So, now I've only told 2 people how long and one thinks I'm nuts, but she's my best friend so that's all she's said and we don't talk about it and other is about 150-175# overweight and knows all about it, but just can't bring herself to do it, but wants to.
Now, if I get invited out I tell them I'm busy and I've got too much work to do and it works for me without any grumbling.