I've experienced it, but now I've just learned to shrug it off... I just tell myself 'they're just jealous, whatever' etc. etc. cuz it's true, it IS their problem not mine.
It's probably also a matter of self-confidence. Since losing weight (apart from your external appearance changing) you probably exude a more confident aura - and people (esp. women) pick up on that, and perhaps they feel threatened or insecure and that's so sad!
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When I see a woman who looks fit and healthy my first thought is, "Good for her!" or "awesome figure" in an admiring way especially since I know it is really hard work to get to that point and then maintain.
Even if I'm out with DH I sometimes I may make a comment to him about another woman having an amazing figure, or that she's pretty, and he may agree with me (or not, depending) but I'm sooo not threatened by that (but years ago in my insecure days, I would be extremely jealous of any other woman he looked at, whether I pointed her out or not
) I've learned to accept and appreciate beauty in other women and that it IN NO WAY diminishes me as a person or how I feel about myself because I'm not competing with anyone - what's the point?
It's just recognising and appreciating beauty/health and/or confidence in another individual. So, yeah, I'm with you, it's unfortunate when you come up against negativity like that... and it is a double bind especially if you've come from a place of self-loathing and low self-esteem to begin with. I guess that's just another hurdle on the journey.