Calorie sources are wide-ranging. In a self-supported ultra, one can take in calories in almost any form. Aid stations typically provide the basic fare of energy drink, pretzels, crackers, cookies, potatoes, candy, and a wide array of other food. A constant battle for many ultrarunners is stomach distress during races. The reason it is such a common problem is the inability for the stomach to perform gastric emptying while running.
Solutions vary, but the key is prevention.
Understanding some basic requirements and rules goes a long way in helping run a better and more trouble-free ultra. Draw out a plan for your energy requirements. Obtaining 50 percent of your calories from a liquid mix and 50 percent from solid food intake is a good starting point. King suggests targeting a regimen of calories per mile equal to the distance of the run in miles. Runners pushing a hard racing pace may have to settle for calories at a lower rate.