Dec 1, 2015
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
You can connect with Dr. Jeukendrup:
Here are some of the questions Dr. Jeukendrup answers:
- On a daily basis, what are the carbohydrate needs of an ultra
- How many calories can most people digest and absorb per hour
- What is the fate of consumed carbohydrate relative to stores
- What are the key factors to be considered with respect to the
carbohydrates during a long event that may last 24 hrs?
- Can we predict when relative glycogen depletion might occur in
an ultra marathon?
- What should we consider when we are choosing specific
- What are the key issues to consider relative to the timing of
carbohydrate intake prior to, during, and following training
- What about timing of carbohydrate consumption for a race
- Is glycemic index of a given food different when running vs at
- 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
- 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
- Is consumption of foods that contain protein, fat, or fiber a
concern in light of effects on gastric emptying?
- 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?
- Can carbohydrate consumption keep us from reaching a muscle
and/or liver glycogen depleted state?
- What is the relation between carbohydrates (type, source,
complexity?) and likelihood of GI distress?
- 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
- How does caffeine ingestion interact with endogenous and
exogenous substrate utilization?
- 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
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
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?