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HEALTH | 18.06.2021

How to avoid digestive discomfort in a marathon

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Gastrointestinal disorders are one of the most common problems for long-distance runners, particularly those who run marathons. We asked Alessandra Huerta, a nutritionist who specialises in sports nutrition, why these disorders occur and how they can be avoided.

What happens to the digestive system during a race?

During a race the sympathetic nervous system is stimulated, and this produces a relaxation of the entire digestive system leaving its function compromised. Blood is directed and concentrated to the oxygen-demanding active muscles, especially to the legs, taking water away from the stomach and intestines.

What does this imply?

As a result, the processing of liquids and food is less efficient, accelerating gastric emptying, increasing the permeability of the intestinal mucosa that alters the absorption of nutrients and accelerating the passage from the colon to the rectum. This, coupled with physical factors due to the impact of stride, rhythm changes, stroke intensity, weather conditions, dehydration and inadequate food intake can lead to the need and urgency of defecation.

To a greater or lesser extent these symptoms directly affect performance, causing decreased running pace and even abandonment, if the symptoms persist.

Who is more susceptible to digestive discomfort?

It can affect individuals differently, with runners who have a prior history of gastrointestinal problems more likely to suffer from it. It is most prevalent in women, beginners and individuals with a lower training level.

What should we do in order to avoid it?

Follow a diet and hydration plan and put it into practice during workouts. This way the digestive system will get used to digesting and absorbing food in these conditions and it will give you  an understanding  of you can eat before and during the race, as well as how much water, isotonic drinks or gels to consume.

How about carbohydrates?

A low consumption of carbohydrates can cause hypoglycemia and nausea. On the other hand, high concentrations from a rapid intake of sports drinks, bars, gels, etc. can cause abdominal pain and osmotic diarrhea, losing large amounts of fluid with an increased risk of dehydration. Therefore:

  • Do not mix isotonic drinks with other sugar-rich supplements.
  • Alternate the intake of isotonic beverages with water (accompanied or without gel) at the supply points.
  • Frequently ingest small amounts of gel to help  prevent stomach aches.
  • Avoid drinking liquids with high concentrations of carbohydrates (+10%).
  • Avoid foods and beverages with high concentrations in fructose. Its assimilation is slower than glucose and can saturate its absorption at the intestinal level. Mixes that combine fructose-glucose do not usually cause discomfort.

How does dehydration affect the digestive system?

Dehydration increases the onset of symptoms with the higher the level of dehydration, the higher the gastrointestinal symptoms.

It is important to make sure you drink enough water to optimize hydration in the days leading up to the race and especially the previous 24 hours, as well as to avoid the intake of alcohol on a daily basis or the day before the race.

What should we take into consideration before the race?

It is vital to respect timing when eating: the last meal should have minimum margin of two hours to ensure digestion.

It is important to avoid foods high in fibre and fats during the morning of the race or even the day before. They slow down gastric emptying, increasing the chance of stomach pain, reflux, vomiting or heartburn.

Leave out spicy and highly seasoned meals in the hours before the race.

And keep in mind that uncontrolled use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, naproxen or aspirin damage and increase the permeability of the intestinal mucosa causing digestive disorders. They are very commonly used before and during competition.

Any final advice?

In the case of repeatedly suffering from abdominal pains, cramps or diarrhoea related to sports activity it is important to go to a gastroenterologist to get  a clinical-sports history and rule out possible intolerances or food allergies. Then you can work with your  sports nutrition specialist on a personalized nutrition plan to support your activities.