This article is from the Running FAQ, by Ozzie Gontang with numerous contributions by others.
(Rodney Sanders email@example.com)
Some general advice to take care of loose bowels.
(1) Look for offending foods in your diet. For example, many people have a
lactose intolerance which can cause all sorts of fun if you had a triple
cheese pizza the night before the run...
(2) If you run in the morning, eat lightly and early the night before... I
try to make sure I eat the least problematic foods close to my workouts...
I've personally found baked chicken/fish, baked potatoes, and pasta with
light sauces (no alfredo!), to be pretty good...
(3) I read that Bill Rodgers drinks a cup of coffee in the morning before
heading out...The caffeine stimulates one to take care of things completely
before getting out...This has helped me when I run in the morning....
(4) Carry a wad of toilet paper with you!
I suspect that if you monitor your diet closely, you'll probably find
something that makes the problem worse than at other times and you can
avoid that food...
Some other advice: (Sanjay Manandhar firstname.lastname@example.org) 1.
Less fiber in the diet 2. Run repeats on small loops.
3. Note all the washrooms along the route. 4. Time of day. For me, mornings
are bad. In the evening runs the problem is infrequent. 5. A primer run. If
I have to run in the mornings, I run 1 mile of primer run so that the
bowels can be taken care of. Then I start my real run.