FOODS TO AVOID BEFORE RUNNING
Try limiting or eliminating some of these foods before running to see if it makes a difference:
High-fiber foods: Whole-grain foods, vegetables, legumes, and fruits that are high in fiber can cause gastrointestinal distress or diarrhea. While those foods are excellent, healthy food choices for runners, they may cause digestive issues in runners who consume them the night before or morning of a long run.
High-fat foods: Foods with a lot of fat -- such as fried foods, cheese, hamburgers, or bacon -- digest slowly and will feel like they're sitting in your stomach.
Caffeine: Coffee or other caffeinated beverages can cause stomach issues or diarrhea. (Although some runners, especially regular coffee drinkers, can tolerate it without problems.)
SAFE PRE-RUN FOODS
These are the best types of pre-run foods to help avoid gastrointestinal distress during or after running:
Refined Carbs: Processed white foods, like regular pasta, white rice, and plain bagels are good choices. Although they're not as nutritious as whole grain and unprocessed foods, they're easier on your stomach because the whole grain is already broken down. A plain bagel with some peanut butter (and a glass of water) would be a safe choice before a long run.
Low-Fiber Fruits and Veggies: If you really want to eat fruits or vegetables before runs, zucchini, tomatoes, olives, grapes, and grapefruit are all low in fiber.
Safe Dairy: Some people have issues when they consume dairy products before runs. Soy, rice, and almond milks generally don't contain the sugar lactose, which can be tough to digest. You can also try acidophilus milk and yogurts with live cultures, which contain bacteria that help with digestion.