Gastrointestinal Troubles During Exercise

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Written by: Stephanie Boville MSc, RD, Registered Dietitian

Do you ever experience stomach pains, burping, nausea or flatulence during your workouts? If the answer is yes, you are not alone. Gastrointestinal (GI) issues are common in athletes, specifically endurance athletes. In fact, 30-50% of endurance athletes struggle with (GI) issues and is a common reason for underperformance. In this article you will learn how a few nutrition tactics can help you have a GI issue free workout!

Why do we experience these GI issues?

There are a few reasons why with intense prolonged activity there seems to be a higher prevalence of GI issues:

  1. Increased blood flow to the muscles and away from the gut may result in malabsorption of nutrients
  2. Increased blood flow to the muscles and away from the gut may result in damage of the gut lining resulting in bacteria and nutrients passing through the gut (increased permeability leading to endotoxemia)
  3. Delayed gastric emptying (ie slower movement of the food from stomach to intestines) can cause upper GI issues such as nausea, reflux or burping
  4. Changes in transit time of food which leads to speeding up or slowing down of food movement through the GI tract

Interesting note: research on marathon runners showed that the gut damage is highest in those who ran their marathon fastest yet had the least symptoms, leading the researchers to believe that some people are more sensitive to the higher levels of gut permeability and damage. One other possible reason for this is the individuals gut microbiome, where an imbalance of good and bad bacteria (dysbiosis) may be the difference between having symptoms or not.

What can we do about it?

First off, you want to consider if your GI issues are constant. If the answer to that is yes, you should consult your doctor to rule out any underlying GI diseases such as Crohn’s or ulcerative colitis.

Secondly, you want to make sure you use good nutritional habits prior to making major changes to the diet like we will discuss below. First things to consider are meal and snack composition and timing. Eating the wrong thing too close to exercise can lead to inadequate time to digest the food leading to cramping and stomach discomfort. Keeping balanced larger meals 3-4h before exercise is recommended. As you move closer to the exercise, consuming smaller, more carbohydrate based snacks tends to work best. Avoiding high fat, high protein, high fibre foods close to exercise can be another strategy to reduce stomach discomfort. Limiting coffee/caffeine and lactose (sugar in milk/yogurt) close to workouts can be helpful. It is also important to train the gut to handle carbohydrates during your workouts (if exercise is lasting over 1h), and NEVER EVER try something different on competition day.

Fruits in cloth bag

What about Gluten?

If you have tried the above recommendations and are still finding it difficult to make it through your workouts and races without GI issues, there are a few new strategies that have been researched. Gluten is often eliminated by elite athletes on the assumption that it causes them GI pain. About 40% of non-celiac athletes will eliminate gluten for at least 50% of the year due to GI reasons. Although they anecdotally find this helps reduce symptoms, research does not always support this and often shows gluten elimination in non-celiac individuals does not result in decreased GI symptoms or inflammation.

Another line of thought regarding why athletes anecdotally see GI improvement when eliminating gluten-rich foods is they are also eliminating fructans (which are considered to be a FODMAP). The low FODMAP diet can be helpful for individuals who suffer from irritable bowel syndrome to reduce GI symptoms.

FODMAP’s are a collection of short chain fermentable carbohydrates. If they are mal-absorbed and or are present in the colon they can be used to feed the good bacteria (prebiotic) causing gas, bloating and other GI symptoms.

Fermentable

Oligosaccharide- carbohydrate chain with 3-10 sugar units (barley, rye, black beans, cashews,   garlic, onion, beets)

Disaccharide: carbohydrate chain with 2 sugar units like lactose (cows milk, yogurt, sour cream)

Monosaccharide: single sugar unit like fructose (found in fruit, apples, fig, mango, pears and sweeteners like high fructose corn syrup)

and

Polyols: sugar alcohols found in sugar free gum and candy (sorbitol, maltitol, xylitol)

A recent research study by Wiffin et al. (2019) investigated the effect of a short term (7 day) high and low FODMAP diet on GI symptoms during exercise. They had 16 participants (both male and female) complete the two dietary interventions in a random order with a one week wash out period between trials. They found that low FODMAP diet resulted in overall improvement of GI symptoms. On an individual basis 69% of the participants reported a positive effect of the low FODMAP diet on symptom management, specifically for pain and bloating. They also show that participants perceived they were able to train more frequently and intensely on a low FODMAP diet.

Warning: Low FODMAP is not a lifestyle!

Low FODMAP should not be followed on a daily basis as it can be restrictive and alter your gut bacteria as these carbohydrates are important prebiotics (they feed the good bacteria in your gut). It is also important to make sure you have a good dietary plan if you follow this diet to make sure you have adequate carbohydrate provision for your activity, especially if you are trying this before a competition. Following the diet for 3-7 days prior to an important event is recommended if you do find it helpful to reduce your GI symptoms. If you continue to have GI pain during training, doing a FODMAP elimination and reintroduction technique should be used to find foods that you are more sensitive to and determine how much your body can handle.

Recap:

  • Is your GI pain occurring all the time? If so, seek medical advice and testing
  • Look at meal timing and composition to reduce GI pain
  • Potentially employ a short term low FODMAP diet prior to important athletic events
Stephanie Boville dietitian GRSM Cambridge
Stephanie Boville MSc, RD
Registered Dietitian

Stephanie Boville joined GRSM June 2019. Stephanie is a Registered Dietitian who specializes in sport nutrition. She has completed her BASc degree in Applied Human Nutrition, MSc degree in Exercise Nutrition and Metabolism, both at the University of Guelph, and a professional Dietetic internship at London Health Sciences Centre. She is a regulated health professional with the College of Dietitians of Ontario. In her spare time, she enjoys learning the art of Olympic Weightlifting, baking and spending time outside. Her philosophy is that all food fit in moderation and truly believes that nutrition can have a huge impact on our sport performance and health.

References:

Lis, Dana M. Exit gluten free and enter low FODMAPs: A novel dietary strategy to reduce gastrointestinal symptoms in athletes. Sport Medicine. 2019. 587-597. https://doi.org/10.1007/s40279-018-01034-0

Wiffin Melanie, Smith Lee, Antonio Jose, Johnstine James, Beasley Liam, Roberts Justin. Effect of a short-term low fermentable oligosaccharide, disaccharide, monosaccharide and polyol (FODMAP) diet on exercise-related gastrointestinal symptoms. Journal of the International Society of Sports Nutrition. 2019. 16:1. https://doi.org/10.1186/s12970-019-0268-9

Sigma Nutrition Radio Danny Lennon Episode 246 with Jamie Pugh- Gastrointestinal Symptoms in Athletes.

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