How do I (23M) tell my girlfriend (23F) that I'm not sexually attracted to her anymore?

Hello!
I want to be as clear and concise as possible, my girlfriend has gained a lot of weight in the past few months, she has always been a person with weight problems, but what a few years ago could be classified as overweight, it is more than visible that it became obesity.
I have tried to convince her to have healthy habits, but she refuses or says "funny" comments like "Exercise is for fat people", I have noticed that she expects me to respond something like "you look good" or "you are not fat", but frankly it's impossible and I only respond with a curt "Oh, okay".
I haven't wanted to have sex with her in the past few weeks, even refusing or making excuses from work/college assignments to avoid going out with her if the opportunity ever presents itself. She has been insistent but I really don't think I can do it.
Frankly, I no longer find her attractive at all, and I want to find a way to let her know without hurting her feelings, I don't want to lose her, but if she refuses to change her habits, both for health and aesthetics, I don't know what direction our relationship could take.
I appreciate any advice you can give me, thank you very much.
Edit:
1.- I am not going to leave her, I love her and I am worried about her.
She has taken many habits that are not healthy at all, and yes, it sounds bad that I am no longer physically attracted to her, but it is the truth, I do not want to lie to her, that would hurt her more to tell the truth.
That's precisely why I want to fix this and find a way for her to work on herself, to prevent more things like that from coming up.
2.- To all those who tell me that she deserves someone who loves her for who she is (Mostly women).
I love her for who she is, which is precisely why I don't want her to change and become a completely different person. She wasn't like she is now and she didn't have these habits either.
TD:LR: My girlfriend gained a lot of weight and I don't find her physically attractive, I want to find a way to tell her without hurting her feelings.


Source.