They sound like they've been good and thoughtful friends in the past.
They sound quite politically aware, but I think haven't self reflected on the impact on you of what they're saying, it's a bit 'knee jerk'.
Also humans don't always embrace change readily.
Given they've always been good friends, I would talk to them about this. Good relationships are worth fighting for, in this case I would be talking to them and seeing how they react to the conversation...
You could acknowledge that they might have some responses which come from those big picture concerns like 'should women have to be thin to be successful and loved' (no),
Agree it is worrying that complex interconnected forces of food types and their availability, societal structures and culture has created a situation where so many people struggle to be at a healthy weight and struggle to change, thus need injections to help.
But then, remind them that you aren't and can't be responsible for those issues beyond how you care for yourself.
Tell them that you were pre-diabetic and now aren't, which means you've avoided a serious health issue.
Ask them to remember you are still you, that nothing you've done for yourself changes how you feel about them, but the peer pressure they put on you when you last got together spoiled your meal, they put you under a microscope and you felt judged and uncomfortable.
Ask them to remember that if we aren't judging someone for being fat then we shouldn't be for being thin, and while some of the things they talked about with you are valid concerns on a wider level, for you as an individual all you've done is look out for your own long term issues and used a tool that's available, which happily did help.
Tell them that though people can feel that they 'should' be able to lose weight from will power alone, and many many people have internalised that expectation... The reality is often far far more complicated and include all kinds of emotional and food relationship issues which means it may not be that simple.
That calling the injections a 'short cut' belittles those complex issues for someone who needs that support. Would they point a similar finger at someone using nicotine patches to get off cigarettes for instance? Food might not be cigarettes, but it's misuse can still give health problems and if anything it's harder to to be something a person struggles with as you can't completely abstain!!
Ask them, to remember that there is an individual they care about here, who doesn't deserve to feel the weight of their displeasure being placed upon her when she thinks she's enjoying time with friends who she thought valued her whatever her body shape.
It puzzles me that friendships are the relationship some people expect to never need to discuss between the people in it... All relationships can benefit from a heart to heart about things... Why should friendship be the one relationship that either works or doesn't and when an issue arises we just cut and run.
If you talk to them and they stick to their attitude and how they have treated you since this change then yes, revaluate the friendship... But it's worth fighting for first isn't it.
Given the chance to self reflect where their disapproval is coming from, and whether they really want to channel it into making you unhappy in the group could be all they need to realise what they're doing and stop.