Trying to manage your weight??
According to a recent study by the USDA, you'll lose 18.8 pounds in one year by upping your daily fiber intake from 12g to 36g.
-Men’s Fitness magazine, May 2007, p 33.

How much is that extra body weight slowing you down? According to a recent article in Runner's World magazine every extra pound of body weight is equivalent to 2 extra seconds per mile.

Therefore if you are carrying ten extra pounds while running the Army 10 miler it will slow you down 3 minutes and 20 seconds (10 X 2 X  10 = 200 seconds).
This article specifically is referring to running but it would be safe to assume that a similar rough estimate can be used during both cycling and inline skating.