Dunno if you have had any probs with this before, but a former international marathoner told me that avoid the shits, I should eat a hard boiled egg before my normal breakfast. i did this before every long run and in my marathon training, and on race days. it definitely worked for me! In the days 'pre-egg', lets just say it was a problem....
Thanks, this certainly wasn't the first time it's been an issue, it's something I'm trying to keep under control with various experiments of pre-running nutrition! Not tried the hard-boiled egg option though, will give that one a try. Imodium is my tried and tested fall-back option!