I used to lift weights all the time in college.... now at 38 yrs, I just can not stand the thought of working out. Or running. I tried doing that P90x thing with my wife and I got bored.. or lazy.
Everytime I see someone running, I say to myself, 'That does not look like fun.'
I DO like riding my mt. bike. We have some great *flat* paved trails around here. I guess the key is finding something you enjoy doing. Otherwise it will just seem like a chore.
But fitness with a poor diet isn't any better than no fitness and a great diet, IMO.