I agree. I'm a thin, athletic woman with a healthy appetite and plenty of would-be suitors. If anyone makes a comment on how much food I eat (and it has happened before), he gets dropped quickly. I've got a good metabolism and genetics, my mother loves food just as much as I do and she's not at all fat.
There are many ways in which a spouse could be rendered sexually unattractive. Thyroid cancer can literally reduce your metabolism to only 200 calories a day (that's 2 apples). A Freeper (forgot her name) had that and she went from 100lbs to 190lbs in 2 months. Also, you can be burned beyond recongition, wheelchair bound, etc.
If men don't think they can take the "in sickness" part, they shouldn't marry. Elizabeth Edwards was on fertility drugs to conceive a child at an advanced age--a decision I don't agree with in the first place, but fertility drugs do have a great impact on weight (not to mention the resulting pregnancy). Likewise, if women can't take the "for poorer" part, then they shouldn't marry either.
Note: I'm not being sanctimious about Elizabeth Edwards... just using her as an example of someone who most likely had less control over her weight than, say, a 30-year-old housewife with no health or fertility problems.
That is incorrect -- you would be dead if your metabolism dropped that low, as just the basic operation of the brain requires more than 200 calories per day.
For people with completely non-functional thyroids, the metabolic levels are typically in the 1200-1400 calories per day range. Not coincidentally, this is the calorie intake level of people with perfectly normal thyroids who are on caloric restriction diets, and is generally recognized as the biological floor for weight maintenance in humans. Anything less than this and your weight WILL drop no matter how messed up your metabolism is.
In the worst case scenario, you would have to eat the same kind of diet that the caloric restriction folks do, which is mainly vegetables, lean poultry and fish, and a bit of nuts and cheese for fat.