Proper nutrition during ultraendurance races is critical for the maintenance of energy balance and a state of euhydration. Nutritional concerns can be divided into two major areas: nutrition during training and nutrition in preparation and during competition. Energy intakes of ultraendurance triathletes during training may vary widely, depending upon duration, intensity, and type of exercise training. Inadequate caloric intake can lead to chronic fatigue, weight loss, and impaired physical performance. Additionally, carbohydrate content of the diet can greatly influence feelings of fatigue. It is not known whether inadequate carbohydrate following exercise limits subsequent training efforts on the same day for triathletes. Inadequate micronutrient intake of vitamins and minerals can also impair physical performance. Nutrition during the 4 h before competition can significantly affect performance, as can carbohydrate feedings during an ultraendurance race. Further research is needed to determine appropriate feeding schedules during ultraendurance events.