How well you tolerate consuming sports drinks and energy gels and how well you can absorb the energy in them and use to fuel your performance are both trainable factors that are critical for endurance performance. 

• Training the Gut methods to improve your tolerance of sports nutrition products and reduce GI-distress.
• Training the Gut methods to improve how much carbohydrate you can absorb and use as fuel. 
• A two-week Gut Training protocol.
• Why "Train low, race high" is not a smart, and definitely not evidence-based strategy. 

5:00 - 

• Information based on: Training the gut for athletes, by Asker Jeukendrup, Sports Medicine, 2017. 
• Gastro-intestinal (GI) problems are very common in endurance sports.
• 30-40% of athletes experience GI problems regularly.
• The causes are largely unknown, but appear partly genetically determined and highly individual.
• Mechanisms are likely to be different for upper and lower GI problems.
• Symptoms are more likely to occur, and are exacerbated by hot weather conditions and dehydration.
• Although a link with nutrition intake is not always found, certain practices do correlate with incidence of GI problems.
• E.g. fibre intake, fat intake and highly concentration carbohydrate solutions all seem to increase prevalence of GI problems.

7:15 -

• In racing and training you need to consume energy.
• Your glycogen stores are limited and need to be topped up.
• The guidelines are to consume between 60-90g of carbohydrate per hour.
  • If you only consume one type of carbohydrate (e.g. glucose), you can only absorb 60g so you should only take in 60g per hour.
  • If you have multiple carbohydrates (e.g. mixture of glucose and fructose), then you can absorb up to 90g of carbohydrate per hour so you can aim for this higher number.
    • There are different transporters in your intestines to transport different types of carbohydrates.
• There is less risk of GI distress when you go for 90g of multiple sources of carbohydrates, compared to 60g of one single carb source.

9:08 - 

• There is a useful visual graphic about this in the review article.
• The first method is training with relatively large levels of fluid intake to train the stomach.
• This reduces bloating and fullness during exercise.
• It can also increase gastric emptying.
• The second method is training immediately after a meal.
• This has the same two effects as above.
• It can also increase your capacity to absorb carbohydrate.
• The third method is to train with high carbohydrate intake during exercise.
• This would be in the 60-90g per hour range.
• This has the same three physiological effects as described above.
• The fourth method is to simulate the race with your race nutrition plan.
• This can be more specific that consuming the same amount of carbs - it can involve the same intensity you expect to do on race day.
• It can also involve the expected conditions of the race (e.g. heat).
• You will see if you can still tolerate the energy you plan to take in under race conditions.
• The final method is to increase the carbohydrate content of your diet (depending what your diet currently is).
• This can improve your capacity to absorb carbohydrate.
• All of these physiological effects lead to reduced GI problems and increased delivery of carbohydrate to the muscles.
• These factors ultimately result in improved performance.

11:50 - 

• There's a study by Lambert and colleagues which showed that trained runners were able to comfortably tolerate ingestion of a carb-electrolyte solution approximately equal to their sweat rate.
• This was done over 90 minutes running at 60% VO2max.
• It was done in 25 degree Celsius heat, 30% humidity.
• The researchers observed that their comfort doing this improved as they practiced with fluid high intakes repeatedly.
• Consuming as much as you sweat in these conditions is a lot of fluid.
• Training for intake of larger fluid volumes can be a good strategy to avoid discomfort in races.
• This is especially important if you feel discomfort with relatively small volumes of fluid.

13:10 - 

• The review articles suggests that in addition to an increased absorptive capacity, this kind of training makes carb ingestion in training and racing easier to tolerate for the gut.
• Gastric emptying can also be improved with this practice.
• Gastric emptying is usually not considered a limiting factor, but certain conditions can combine and compromise gastric emptying - for example heat, high carb intake and high intensity.
• It's important to practice high carbohydrate intake in general, but also at race intensity and in race conditions.
• This is particularly important if you have a hot race.

14:28 - 

• We don't know what the exact link between daily carbohydrate intake and transport capacity for carbs in your bloodstream is.
  • Some studies indicate that there can be a strong link.
  • They suggest that we can improve our capacity to transport and absorb carbohydrates by increasing the percentage of carbs we eat in our daily diet.
• One study investigated 16 trained cyclist divided into a control group and a high carb group.
  • They trained 16 hours per week for 28 days.
  • The baseline diet for both groups were 5g of carbs per kg bodyweight per day.
  • The high carb group had a supplement with an additional 1.5g of carbs per kg body weight per hour of exercise added to their diet.
  • Both groups improved performance a similar amount.
  • The high carb group managed to improve how much exogenous carbs (e.g. gels/sports drinks) that they could use for fuel during training and races.
• Not all carbs that you take on can necessarily be used by your muscles, some will go to waste.
  • This was improved in the study by training with a high carb intake.
• The review study goes on to say that for a single source of carbohydrate (e.g. glucose), transport capacity hardly ever exceeds 60g per hour in individuals.
  • There is likely a limit to how much you can train your intake.
  • If you're already on an endurance diet with a high level of carbs you may not see big improvements by increasing your intake further.
• If you are on a low carb diet or a ketogenic diet, you could see your ability of carb transportation improve quite drastically.
  • This can happen within 3 days to 2 weeks.
• One study, based on animal data, found that an increase in dietary carbohydrate from 40% to 70% of the daily calorie intake doubled the amount of carbohydrate transporters in just two weeks.
  • Other studies have found even shorter time periods.
• This is an important argument against the recent media hype around "train low, race high" strategies.
  • From what I've seen, there isn't any research that speaks for the train low, race high strategy, but the evidence we've discussed here clearly shows that this strategy may in fact reduce how much you can benefit from your energy consumed from gels and similar products.
• A recent Australian study is useful for illustrating this - Two weeks of repetitive gut challenge reduces exercise associated GI symptoms and malabsorption.
  • It's the first study to investigate training your gut to consume gels.
  • The study involved 18 trained runners.
  • They had a test that included 2 hours of steady running at 60% of VO2max, followed by a 1 hour time trial.
  • In the first 2 hours they consumed 90g of carbs per hour (3 gels, each with 30g of carb in a 2:1 glucose to fructose ration).
  • All of the subjects had at least moderate GI symptoms, and 67% of them had severe symptoms in the first trial.
  • 61% of them had malabsorption of carbohydrate - not being able to use as much of the consumed energy as expected.
  • The athletes then went into a period of gut training for two weeks.
    • 10 days of training doing a 1 hour run each day at 60% VO2max.
    • Half took 90g of carbs each run (1 gel every 20 minutes).
    • The other half just had placebo gels (no carbs).
  • They then repeated the baseline test - 2 hours steady running and then a 1 hour time trial.
  • A lot of the participants still had some GI symptoms, but the gut trained group had a 44% reduction in discomfort and 60% reduction in total GI symptoms.
    • The gut trained groups also had less carb going to waste.
    • None of the gut trained group has severe symptoms, they were moderate at most and for some completely gone.
  • The placebo group didn't change in any of these.
  • The gut trained group improved their performance by 5%, while the placebo group didn't improve performance at all.
    • This is likely because they were able to absorb more carbs, and were not struggling to run with GI discomfort.

Links and resources mentioned

• Race-day fueling and The Core Diet with Jesse Kropelnicki | EP#40
• Nutrition before, during and after workouts | EP#100
• Training the Gut for Athletes - Asker Jeukendrup, Sports Medicine, 2017
• Two weeks of repetitive gut‐challenge reduce exercise‐associated gastrointestinal symptoms and malabsorption, Miall et al., Scandinavian Journal of Medicine & Science in Sports, 2017
• The New Science of Training Your Gut - Sweat Science
• Fluid tolerance while running: effect of repeated trials. Lambert et al. 2008
• Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. Cox et al. 2010.
• How to shave 14 minutes off your Ironman bike split with Jon and Chris Thornham | EP#31

Connect with host Mikael Eriksson

Hi! I'm your host Mikael,

I am a full-time triathlon coach and an ambitious age-group triathlete. My goal is podium at the Finnish national championships within the next few years.

I first started the website Scientific Triathlon in autumn 2015 as a passion project to share my learnings with a larger triathlon audience. Later on, in early 2017 I started the podcast That Triathlon Show. 

I sincerely want you to contact me to

• Send me feedback
• Give constructive critic​ism 
• Request topics and guests for the podcast
• Send me your triathlon-related questions 
• Tell me that you've rated and reviewed That Triathlon Show so I can give you a shout-out on the show and tell you how much it means to me!