It's easy to get upset at the offending partner when they make comments like that, but honestly take it from someone who's been married for 30 years, it all comes from a place of insecurity and fear of the unknown....for both of you. You need to help her understand that your journey to a healthier you is only going to make you a happier, more fulfilled person, which in turn should make her happy, too. Try to reassure her how important her love and support will mean to you as embark on this new chapter of your lives. After all, change is a normal, contstant part of life, and the strongest relationships can adapt.
As far as her not being willing to change her lifestyle, you can't control what she does, only how you react to it. YOU are choosing to do this, not her. Find another support system if need be. As long as she can at least emotionally support you, there's no need for her to change her activity and eating habits if she doesn't want to. My husband didn't, and I did just fine. You will too if you REALLY want to. She may also surprise you and come around.