My teenage son gets diarrhea every time he runs long distance. what should he do is he drinking too much or too little? is he over working himself? this is the first time he has run cross country. fyi

That : That is not an uncommon complaint. He should make a food log and running log, and see how his food choices are affecting the diarrhea. With the food log, record also what time he eats and what time he runs. Then he may be able to establish a pattern with the diarrhea. He definitely should not restrict fluid intake. If it continues, if he has any abdominal pain, bloody diarrhea, doesn't improve when you change his eating patterns, or if he has light-headedness or feels faint then he must be seen immediately by a doctor.

Hard to say: Not a common problem so i can only conjecture. I would suspect the vigorous exercise is disrupting his autonomic system enough that it causes diarrhea. The running and diarrhea can both cause loss of electrolytes so replacement is in order. Besides a simple exam/lab might have him see an acupuncturist for 3 sessions to see if that helped along with more gentle pacing regarding his running.