Glucose Is the Preferred Substrate for the Muscle

Science of Ultra   Episode 13   Carbohydrates for ultra marathon training and racing   My guest today is Asker Jeukendrup, PhD. He is a leading sports nutritionist and exercise physiologist who spent most of his career at the University of Birmingham (UK), where he was a Professor of Exercise Metabolism and Director of Research. He worked the last 4 years for PepsiCo as Global Senior Director of the Gatorade Sports Science Institute Based in Barrington IL (US). He is currently running a consulting business “Mysportscience” and is a visiting professor at Loughborough University. During his career he authored over 200 research papers and book chapters, many of which have helped to change the sports nutrition landscape. He is also the author of 8 books. He is the former editor of the European Journal of Sport Science and Associate editor of the Journal of Sports Sciences. During his career he worked with many elite athletes and teams including several World and Olympic champions. He also practices what he preaches and is competing in Ironman distance triathlons as well as other endurance events. To date he has completed 21 Ironman races including 6 times at the Ironman world Championship in Hawaii.    You can connect with Dr. Jeukendrup: www.mysportscience.com Twitter @jeukendrup   Here are some of the questions Dr. Jeukendrup answers:

1. On a daily basis, what are the carbohydrate needs of an ultra endurance athlete?
2. How many calories can most people digest and absorb per hour when running?
3. What is the fate of consumed carbohydrate relative to stores while exercising?
4. What are the key factors to be considered with respect to the carbohydrates during a long event that may last 24 hrs?
5. Can we predict when relative glycogen depletion might occur in an ultra marathon?
6. What should we consider when we are choosing specific high-carbohydrate foods?
7. What are the key issues to consider relative to the timing of carbohydrate intake prior to, during, and following training workouts?
8. What about timing of carbohydrate consumption for a race event?
9. Is glycemic index of a given food different when running vs at rest?
10. For those who don’t like sweet tastes while exercising or late in races, what are the sources of simple carbs that don’t taste sweet?
11. Are there data, or any good reason to expect, that any aspect of carbohydrate digestion/optimal sources/etc. will change over the course of an ultra marathon? Does carbohydrate physiology change when we go way beyond the better understood distance of marathon? 
12. Is consumption of foods that contain protein, fat, or fiber a concern in light of effects on gastric emptying?
13. When we consume carbohydrate during a run but prior to reaching very low levels of glycogen in muscle and liver, are those calories used more/less/equally to stored muscle glycogen?
14. Can carbohydrate consumption keep us from reaching a muscle and/or liver glycogen depleted state?
15. What is the relation between carbohydrates (type, source, complexity?) and likelihood of GI distress?
16. Tell us about the topic of ‘fat adaptation’ to spare glycogen. From my reading and understanding, there is no good evidence that fat adaptation provides any benefit to endurance performance and it may even impair higher intensity performance (like going uphill) by not ‘sparing’ glycogen but rather by ‘impairing’ glycogen utilization…that apparent sparing may actually be a side effect of impaired utilization.
17. How does caffeine ingestion interact with endogenous and exogenous substrate utilization?
18. GI distress late in a race makes it difficult for some people to retain any calories they might swallow. Tell us about this interesting topic of ‘mouth sensing’ and what it might do for us in that situation.

  We wrap up with a couple of focused action items:   1) What are the 2-3 biggest mistakes or misconceptions that you see endurance athletes make regarding carbohydrate and fueling for performance?  2) What advice do you have for runners wanting to dial in their carbohydrate strategies (maximizing calories, best sources for them, etc.) for training and racing?