I promise you that people do not mean to be patronising or to imply that you looked bad before.
Have you lost a significant amount of weight? Have you spent years moving through the world as a fat person? I'm going to guess the answer is no, because if you had, you wouldn't feel confident in making this promise.
They're just telling you that they've noticed the change you've chosen to make and reassuring you that it was a great choice.
You don't think that sounds patronising? Reassuring her that she made a good choice? About her own life? Was she asking them for reassurance?
Basically, other people are being kinder to you than you are being to yourself
Why do you think it's kindness when people dehumanise and objectify you? Who taught you that others are entitled to comment and give their opinions about your body?
Again, there's a simple and compassionate solution to this, which is stop commenting on people's bodies and weight loss unless expressly invited to do so.
OP, I think it's important to acknowledge that your feelings are real and valid, and in fact that while people may 'mean well', their comments are intrusive and make you feel bad. So don't engage with them - brush them off, don't answer, or say 'it's none of your business'. Or change the subject. Don't let rude, thoughtless people derail you from your goals.