well first of all, GOOD FOR YOU!
As long as you are eating the right amount for you, being active and healthy and not starving yourself, hold your head high!
We all know that a lot of women have jealousy issues. I have been experiencing the same thing. And i just respond with "I eat very healthy, am active, and this is the happiest I have ever been." People usually don't carry out their negativity after that…. and if they do… yeah, it's because they are jealous, not "concerned"