Does Fast Riding ==> Fast Bowels?

Question:
Can riding hard cause the digestive tract to go into turmoil?

Background:
I have been bike commuting for 4 years. My commute is ~40 miles round trip. I average above 20mph which for me is sustained 70%-90% effort for 2 hours (1 hour each way). I ride 2-3 days per week.

Result:
On days when I ride, I experience "fast bowels". By that I mean I must visit the stall at work every 2 hours. Also, I get above normal flatus. I wouldn't go so far as to invoke diarrhea, but it is definitely a disruption to my day (without mentioning the chaffing).

I have tinkered with the cause, and the only thing I change is the ride. My diet is not altered between riding and non-riding days.

Am I the only one, or is this a known side-effect of cycling?



Pet hypothesis:
On my riding days, my body's caloric demand obviously spikes. In an effort to fuel the high demand, my digestive tract goes into overdrive - trying to pull as much energy out as quickly as possible. The result is inefficiencies; food arrives in the lower digestive tract partially digested. The bacteria there goes to work on it which results in the described side-effects.

 

If you are riding you are burning more calories- it may very well be possible that you are putting more fluids than solids into your gi tract???

Have you tried eating more to compensate for your riding? Since you say your diet doesn't change...I'd expect you would need to eat more to compensate for the energy output from riding.