food to eat before a long run

Hello I have a question, when I run more than 5 miles my stomach will start to hurt, cramp and then I need to have a bowel movement. I usually run in the morning and have a bowel movement before I run. I usually eat a protein bar, protein drink and water before I run. What can I eat the day before and before I run to avoid the stomach pain and needing to have a bowel movement. I plan to run a half marathon this weekend. Please advise.