Ultra-endurance events such as 100 mile runs and multi-day bike packing trips pose a variety of unique nutrition-related challenges. In this upcoming series of posts we will aim to uncover some of the evidence-based recommendations and recent research findings to help guide your approach to ultra nutrition.
Fatigue during an ultra is multifaceted and associated with multiple factors including cognitive and central nervous system fatigue, heat or cold stress, dehydration, and depletion of stored carbohydrate (glycogen). Environment, remote course locations, terrain demands, and access to refuel points/support add additional challenges.
While fat is a primary fuel source during low intensity exercise, oxidation of CHO is actually more efficient and necessary for higher intensity bursts. However, the amount of stored CHO (glycogen) we have in our body is limited to approximately 1500–2000 kcal in muscle and approximately 400 kcal in the liver. Thus, given that these events are long, glycogen depletion is a concern. Protein, specifically BCAAs, also contribute a very small amount towards energy production, compared to fat and CHO during endurance events. Your fueling plan for an ultra should include adequate CHO intake leading up to the event (carbohydrate loading) as well as during the event. The amount of carbohydrate taken in during the event is going to be highly individual. Early in ultra events, your pace may be higher, making higher CHO intake rates (e.g. ~90-120 g/h) necessary if tolerated. Depending on duration and intensity of the event, decreasing CHO intake rates, while still maintaining steady intake, may be appropriate (e.g. ~30-90 g/h). Individual factors including hydration status, GI symptoms, and CHO absorption (including gastric emptying and gut absorption) and uptake rates into muscle, and actual CHO utilization rates also influence individual fueling recommendations over the course of a long event.
For events longer than six hours, you will likely want to use a variety of foods and fluids in solid, gel, and/or liquid forms, including water and carbohydrate-electrolyte sports drinks, sport-specific nutrition products (bars, gels, chews), and easily-digestible regular food (rice cakes, chips, pretzels, soup, potatoes, PB&J, etc.). While a small amount of protein and fat is generally tolerable in ultra events, it remains that carbohydrate intake is the most “gut-friendly” option, maintaining integrity of the gut lining more effectively than protein and fat. In a high stress event like an ultra, reducing stress and inflammation related to the gut is important. For athletes not accustomed to higher carbohydrate intake rates, it is recommended that the athlete complete a ~ 2 week gut training protocol with event-day simulations prior to the event itself.
PMID: 30056753; 21775906