My spouse is and has always been quite overweight. From the beginning it was no problem for me, I just don't mind.
Yet, since we've been living together, my spouse somehow put on a lot of weight (over the course of several years). Mostly because we are both connoisseurs of fine food and whenever we spend time together we tend to eat quite generously.
But it has come to a point where it is dangerous for my spouse's life in the long term, and even though we talked about it... I doubt she really listened to me. As far as I can tell, she thinks "Yeah, yeah, I'm going to be more cautious, I will make sure not to put on more weight!" and when I'm with her that's definitely what she does. Yet when we talk about what we eat when we're not together, I clearly understand that she is far less cautious without me. And even though she perhaps doesn't gain weight that's just one part of the problem... Losing some would be important for her health.
Now, I need to talk about this with her seriously, without being rude because that's not my goal. Problem is: she dismisses easily everything I tell her because "she knows best". Which is true on some level, she knows exactly what to eat or not to, but doesn't apply her own advice. Even when I could point out some irregularity in her diet, I just can't say it without sounding rude.
My goal is not to blame her for everything she eats, but merely to pinpoint some excess she does once in a while and which does not help her at all. All in all, my goal is to help her in the long run, because it has gone too far.
Any idea on how to approach her about this problem?