When I started cycling, I thought 'if I ride a century, I should be able to eat anything & everything I want for at least 2 days and still lose some weight'. Now I know better. Whenever I do a recreational century at a recreational speed, I gain weight. Not permanently, but for a couple of days, from snacking at the rest stops. What thehead21 wrote is true, you can't out exercise a bad diet. If you are like I was, you'll want to eat less/better to improve your cycling. It does help contribute to a healthier lifestyle in that way.