1. Avoid bowel-stimulating substances. Caffeine ranks as the most common intestinal irritant, followed closely by alcohol and high doses of vitamin C. Some people can't handle various sugars, such as lactose (milk), fructose (fruit), sorbitol and mannitol (both sugar substitutes).
2. Eat light. Try low-fiber carbohydrates like bananas, cooked oats (without added sugar) and toast before a run. Bananas make a great pre-race food because they're high in nutrients and easily digested.
3. Go before you run. Establish a pre-run bathroom routine. A light meal or a cup of herbal tea can trigger the urge to go to the bathroom.
4. Avoid highly concentrated beverages. Most bottled sports beverages contain 5 to 8 percent carbohydrate. Beverages more concentrated than 10 percent can delay stomach emptying and draw water into your intestinal tract, causing loose stools.
5. Gradually boost your exercise level. When you're in top condition, your muscles use oxygen more efficiently, allowing more blood flow to your intestines. If problems cause you to cut back your mileage by, say, 50 percent, move back up by only 10 percent each week.
6. Stay hydrated. Make sure you've had enough fluids before you begin a race or workout. Carry fluids with you everywhere and take frequent sips. The morning of the race, drink two 8-ounce cups when you get up, then down one or two cups at every aid station.
7. Consider a new training time. Morning workouts most often stimulate a bathroom call.
8. Calm down. Anxiety can cause diarrhea. Relaxation techniques that may help include yoga, meditation and deep breathing. Conjure up a mellow state before a race or workout.
9. Find a routine and stick to it. A few weeks before the race, find out the brand of sports drink that will be offered at the aid stations and practice with it.
10. Consider medication.You can take Loperamide (immodium) in low doses to curb diarrhea. Follow the package directions.