How important should healthy be in a relationship?

Not disease and such, but a healthy weight notwithstanding muscle which weighs more than fat.

The following articles, old as they are, make an interesting point:

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I recently turned 25 and am more fit than I was when I was 19 ( I got fat after freshman year in college ).

I don't understand people in general, who settle in and throw their health to the wind. When I'm 65 I still intend to jog regularly and lift weights. Then again I am a huge Stallone fan ( no I don't support the steroid use ).
How important should healthy be in a relationship?
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