It's called "mind reading" and it's bad. I do it all the time. So do most people. You seem to feel that they are judging your weight, but they may have just been talking about THEIR success or failure at weight loss and someone said "Do you know (Silverfire), she lost 30 lbs before any of us." and they all went "Wow, that's impressive". And someone else said, "She hurt her shoulder". And... I'm mindreading, too, of course (and without even knowing anybody in the group). But my point is that it's normal to talk about co-workers public actions, and by joining the challenge before you made your weight loss public. You can fight mindreading using cognitive thinking - just be aware that you're doing it and substitute more positive words for what you think they are saying, or come up with a positive reason for what the person said. I.E. if someone ignores you in the hall, don't assume it's because you did something wrong, tell yourself that they were deep in thought and simply didn't notice you. It's probably true, anyway.

I doubt they were saying anything negative about you, but it would have made me feel weird too! I find it terribly awkward to receive that much attention. Even though you participate in weight loss competitions with them, their discussing you without you is kind of uncool, unless they were just saying how jealous of your awesomeness they are