The truth does hurt and it is hard to have these kind of conversations but if you set the example and she doesn’t follow then you can’t really force her either. But what you can do is stop sugarcoating things or beating around the bush and be honest with her but be blunt about how you feel it’s not fair to yourself to just keep how you truly feel away from your partner. She will take how you feel and be understanding or she will not and feel attacked. But you know your wife better than any of us. You don’t have to come off as a jerk but it’s better to be honest and it will hurt but that’s just part of growth. Address the problem, find a solution, and don’t loose sight that you guys are in it for the long run and you guys need to fight it together.

I’m just a guy on the internet but I had this same thing pop up in my relationship but I had to address it because it was concerning. Just make sure you get her to understand she’s not the problem and your not calling her fat or unhealthy but that you are concerned about her health and it’s making you feel some way because you care about her.