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More Carbs Correlates With Less GI Distress in Runners

A new study following ultrarunners attempted to answer that age old question: What causes GI problems in long-distance races? There was one important new finding.

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Each month, Dr. Jeffrey Sankoff looks at a recent study or body of research to talk to the researchers, explain the process behind it, and break down the findings.

This month: A study that followed 33 ultrarunners during a 60km event to measure markers of inflammation in the blood and their relation to GI distress.

Race nutrition is a popular subject of discussion and a frequent source of anxiety for triathletes. Specifically, anxiety about getting nutrition in and keeping it down. This is because gastrointestinal (GI) distress is a common complaint among endurance athletes, triathletes included, and something that can undo even the best thought out plans and months of training.

A recent publication may provide some guidance for those who suffer this common affliction in events. The paper was a collaboration between researchers in the Netherlands, Norway, and the United States and looked at ultramarathon runners participating in a 60km race. The researchers were interested in determining how frequently athletes complained of GI distress during the event and whether or not the type and amount of nutrition being taken in had any impact on the frequency and severity of those symptoms. In addition, the scientists hypothesized a specific biological premise that leads to GI distress in athletes—and they set out to find evidence to prove or disprove that theory.

This is important because to date there have been many reasons postulated as to why endurance athletes develop GI symptoms but none have ever been shown definitively to be at the root of the issue.

RELATED: The Science of How Stress Impacts Your Gut Function

These authors believed that during exercise blood flow is diverted away from the organs of the GI tract and this would result in inflammation and injury that in turn would cause all those symptoms that stop you from being able to take on additional nutrition. They set out to prove this by measuring markers of inflammation taken from the blood of the runners obtained before and after the event, looking for generic markers of inflammation that can be present anywhere in the body and for levels of a marker very specific to the GI tract. Intestinal fatty acid binding protein or I-FABP is a marker in the blood that shows up in very specific conditions of inflammation and of damage to the organs and tissues of the GI tract. By looking for this specific marker, the authors hoped to show that GI tract injury was occurring and that this was the cause of GI symptoms.

So what did they find?

There were 33 athletes in this study, 28 of whom were male, and nearly three-quarters of them reported experiencing some symptoms of GI distress. This could have been anything from nausea to abdominal pain to diarrhea. While so many experienced symptoms, very few of the athletes reported these as being particularly severe. In fact on a 10-point scale of severity, with 10 being the worst, the average score was only 1.9—so not exactly anywhere near debilitating.

As to the markers of inflammation, blood samples taken before and after the event did show that the non-specific markers of inflammation did rise, but this was true whether or not an athlete suffered GI distress of any kind (this is consistent with previously reported research on inflammatory markers in exercise). I-FABP levels, though, did not increase even in those athletes with the worst GI symptoms. So gut specific injury and inflammation did not appear to be the mechanism that caused these symptoms. 

The one thing that was associated with symptoms was the amount of nutrition taken during the event. There was an inverse relationship in this regard. That is to say, those athletes that took the most nutrition, and especially when that nutrition was in the form of carbohydrates, experienced the fewest and least severe symptoms.

The reason for this appeared to be that when carbohydrates were being ingested, this improved blood flow to the gut through various mechanisms and prevented many of the symptoms often associated with low blood flow states.

This study definitely has to be interpreted with a certain degree of caution because it was small and included very few women. Still, the findings are consistent with previously published research—though the specific results related to increased carbohydrate consumption being associated with fewer symptoms is new and of interest.

Despite these limitations, the idea that athletes who take in more nutrition in the form of carbohydrates tend to do better with respect to GI symptoms is an important one. This suggests that triathletes who have had issues in the past should consider a race nutrition plan that has them taking in a higher amount of fuel earlier in their event and doing this with carbohydrates as the preferred fuel. 

While this study did not confirm the cause of GI symptoms being inflammatory in nature, it did rule it out, and so the search for specific causes of these problem will continue.

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