Hello, Asklepios, and welcome to PC!
What a great bunch of thoughtful responses you have received here. I recognize many of the conditions you've described, having experienced similar myself. I agree with others' reflections that your wife sounds depressed.
You say she is highly educated, and I'm wondering if she should consider an outlet outside the home for stimulation...perhaps volunteer work or a job, even part-time. Has she ever expressed interest in such a thing? I know for myself when I am off work, I tend to vegitate from lack of stimulation.
It also sounds as if you want this marriage to work, and that you truly love your wife. Speaking as a middle age woman, I can tell you that weight gain, and the physical battle to maintain the girlish figure, becomes harder and harder as we age. Perhaps she senses your expectations and perhaps even resents it somewhat, thus giving in even more to the changes in her body, rather than facing the hard work to stay fit. It does sound unhealthy for her though. The health issues alone, not even considering the aspect of being attractive, are a good reason to start a fitness program.
My advice here is not much help, I realize. I hope the advice of others is more helpful to you.
Sincerely,
Patty