Gut discomfort and physical activity

Gastrointestinal (GI) discomfort including nausea, vomiting, abdominal cramps, diarrhoea and bloating have been reported by active people. GI discomfort during physical activity, sometimes referred to as “runners gut” or “runners trots” can be a problem during training and competition affecting the overall performance and wellbeing of an athlete.

  • Causes of GI discomfort

    Active people commonly avoid eating before, during or after physical activity because of the belief that it can prevent or reduce possible GI distress. Studies have found that a delay or increase in the rate of gastric emptying (i.e. faster or slower movement of foods / drinks from the stomach to the small intestine) can cause uncomfortable GI side effects during exercise. The following are associated with altered rates gastric emptying:

    The nutrient composition of pre-exercise meal: eating a pre-exercise meal high in fibre, fat and protein delays the rate of gastric emptying of stomach contents to the small intestine
    Dehydration: insufficient fluid before and during an event has been identified as a common cause of GI discomfort for athletes as dehydration can decrease the rate of gastric emptying
    Exercise intensity: Training at high intensities (i.e. greater than 70% VO2 max) can delay in gastric emptying by slowing peristalsis in the mid-oesophagus and small intestine.
    Reduced blood flow to the gut (ischaemia): This has been shown to be a cause of GI discomfort because the blood flow is being redirected from the gastrointestinal tract to the muscular system during exercise.
    Eating too close to an event: When eating too close to exercise, this doesn’t allow the stomach enough time to digest the food eaten before moving along the digestive tract.
    The osmolality of beverages consumed: Drinks with with a carbohydrate concentration greater than 10% (e.g. soft drinks, fruit juice and energy drinks) can delay gastric emptying and lead to osmotic diarrhoea as they draw additional fluid into the small intestine.

    There are also causes that are not related to the rate of gastric emptying:

    Stress and/or anxiety can affect the amount of gastric secretions your stomach produces, leading to symptoms of GI discomfort.
    Undiagnosed or poorly managed underlying medical conditions – this may include lactose intolerance, coeliac disease, food allergy, food chemical sensitivities, irritable bowel syndrome (IBS), gastritis, helicobacter infection and Inflammatory Bowel Disease (IBD) to name a few. These conditions can lead to GI discomfort when consuming problematic foods.

  • There is no need to avoid dairy foods

    There is no need to avoid dairy foods before exercise unless there are diagnosed underlying medical conditions. Research has shown dairy can be included in meals consumed before strenuous physical activity without impacting either gut comfort or performance. In addition, excluding dairy food before exercise may also unnecessarily reduce dietary sources of high quality proteins and calcium with possible implications for performance, body composition and health. 

    Individuals with underlying medical conditions affected by dairy should seek suitable alternatives to ensure they are meeting their fuelling and calcium requirements.

  • Gut trainability

    Gut trainability is an adaptive response believed to prevent or minimise GI distress by influencing the rate of gastric emptying in athletes over time as tolerance for foods and fluids increases. Training the gut relies on the athlete routinely eating foods and fluids during intense training sessions and maintaining these habits throughout competition. These adaptations can take up to 20 days to become noticeable.

  • Avoiding GI discomfort

    There are several things athletes can do to avoid GI distress during physical activity without sacrificing their performance, body composition and health.

    • Avoid eating a substantial meal within the 2-4 hours before exercise.
    • If you use sports drink, use a standard concentration sports drink - these usually contain 4 – 8% carbohydrate and are less likely to lead to GI upset.
    • Practice your competition diet during training to ensure that what you are eating and drinking before and during exercise do not cause any GI upset.
    • Begin your physical activity well-hydrated and sip on fluid regularly during exercise to avoid becoming dehydrated.
    • After exercise, milk-based beverages with or without added sodium have been shown to be suitable in hydration as they lead to lower urinary losses in comparison to sports drinks.
    • Devise a gut training plan with your coach and Accredited Sports Dietitian
    • Seek support for managing stress and anxiety to find strategies that work for you

    Most importantly, everyone is different and as outlined above, there are numerous factors that can be linked to gut discomfort during exercise. It is highly recommended individuals consult with a Accredited Sports Dietitian to develop a suitable nutrition plan to avoid GI discomfort during physical activity whilst also enhancing their performance, nutritional balance and wellbeing.

  • References

    Burke L & Deakin V, Clinical Sports Nutrition, 670-691, 2015, 5th Edition, McGraw Hill Education, NSW

    Haakonssen E, Ross M, Cato L, et al. Dairy-based pre-exercise meal does not affect gut comfort of time-trial performance in female cyclists. International Journal of Sports Nutrition and Exercise Metabolism; doi: 10.1123

    Pegoretti C, Antunes A, Manchado-Gobatto F, et al. Milk: an alternative beverage for hydration?. Food and Nutrition Sciences, 2015; doi: 10.4236/fnx.2015.66057

    Stuempfle KJ, Hoffman MD, Hew-Butler T. Association of gastrointestinal distress in ultramarathoners with race diet. International Journal of Sport Nutrition and Exercise Metabolism, 2013; 23, 103-109