 [ Symptoms ] i am having extreme gi issues during and after i run my stomach kills and i feel extremely nauseous what is wrong [ Disease ] i am not sure why this is happening but it is common dairy is certainly a possible culprit but you say you have cut it out before you run here are some additional tips 1 avoid caffeine and warm fluids they can increase intestinal motility 2 limit high fiber foods you may want to track the food you eat the day before too 3 avoid any other foods that you know upset your stomach or give you gas 4 stay well hydrated dehydration slows digestion of food and cause stomach problems i recommend 16 20 ounces of water 60 90 minutes before you run and 8 10 ounces every 20 minutes during the run importantly avoid replacement beverages like gatorade since the sugar can increase motility 6 avoid aspirin ibuprofen products with sorbitol or large doses of vitamin c all of these can cause diarrhea or otherwise upset your stomach 7 try a bland food like half a bagel and nothing else 30 45 minutes before you train 8 pepto bismol can help too 9 if possible empty your bowel before you run if it continues you should consult your doctor to rule out any medical problem