It is disrespectful for her to not take care of the body you both share.

I doubt she would put with with a drug or gambling addiction from you.  Why should you put up with a food addiction from her?  You need to tell her that she needs help with the weight loss, and that you are unhappy.  I would tell her that if she puts no effort in her body, you should be allowed to enjoy someone elses body. 

Before I married my husband, we had a discussion that obesity for any reason save for an extreme medical problem would be a deal breaker.  I take care of my body for him, and he does the same for me.  Anything else is lazy and selfish.  Just as I wouldn't come home with a body full of tattoos and piercings without discussing beforehand, I won't let myself become 300 lbs.  That is extremely fat. 

It's not unreasonable for you to expect your partner to not be obese.