5 common causes of Runner’s gut

Do you ever experience abdominal pain, diarrhoea, bloating or feel nauseous before a race or training session? Runners gut impacts 30-50% of endurance athletes during an event – that’s a lot!!

Runner’s Gut doesn’t just affect runners. Other sporting modalities experience it too, but it is more common in endurance sports such as triathlon, marathon, trail running, and cycling.

Runner’s Gut can hinder sports performance and often causes athletes to pull out of events. Finding the cause and implementing strategies to prevent runner’s gut can help take your performance to the next level.


Below are 5 common causes of Runners’ Gut:


1. Dehydration
Exercising in the heat or for long periods of time without adequate hydration can lead to Runner’s Gut. As our body temperature increases, water is drawn away from our gut and dissipates out as sweat to cool the body down. When losses reach 2% of our starting body weight, regular gut function is impaired and our gut becomes stressed causing symptoms such as cramps and diarrhoea.

2. Highly concentrated carbohydrate drinks
Hypertonic drinks have a higher concentration of carbohydrate than your blood. Hypertonic drinks are those drinks which have greater than 8% carbohydrate. For example, coke, fruit juice and Lucozade. They take longer to be absorbed (slow gastric emptying) and require more fluid to be drawn into the intestines to dilute the concentration to a level that allows absorption. This increases the likelihood of stomach upset. The type of sugar contained in the drink may also play a role, fructose commonly causes GI upset when consumed in larger quantities.

3. Timing of your last meal before exercise
Most people need to allow time for food to digest before exercising. Movement in the gut can cause upset with or without food, however more often upset is caused when food is undigested. Everyone is different as to how they process a meal .The size and composition of your meal will also affect the timing of your food digestion.

4. Type of food eaten before exercise
High fibre, fat and protein meals take longer for the gut to process, therefore slowing gastric emptying. Eating foods high in fibre, fat or protein too soon before exercising can cause GI distress in some individuals. Carbohydrates can be more quickly absorbed and are the preferred source of energy prior to exercise. Therefore, pre-exercise meals or snacks should contain a good source of carbohydrate. However, the dose of carbohydrate still needs to be considered, particularly when consumed within 80 minutes of exercise.

5. Gut related medical conditions
Common gut related medical conditions include; lactose intolerance, coeliac disease, gluten insensitivity, Irritable Bowel syndrome and fructose malabsorption. When these conditions are poorly managed or misdiagnosed GI symptoms may occur, and more often worsen with exercise and particular dietary factors.



Nutrition Strategies to help:


1. Stay hydrated. It is important to start exercise hydrated and have good fluid replacement strategies in place during and post-exercise. A great way to know if you are hydrated is by looking at your urine, which should be a light ‘hay’ colour. It should not be clear (this can sometimes indicate over hydrating). Aim to limit body mass loss during exercise to <2% of your starting weight. A Sports Dietitian can help you determine your fluid losses and help to put a hydration strategy in place. Once you know your losses, you should be aiming to replace 125-150% in the 4-6 hours post-exercise. Some athletes withhold fluids prior to exercise as a way of avoiding GI symptoms but in fact dehydration could be your culprit!

2. Choose drinks that are <8% of carbohydrate if choosing to have a sport drink as a source of fuel. If preparing sports drinks from a powdered form it is important to follow manufacturers instructions. A higher concentration than suggested can cause GI discomfort. Example: if 2 scoops of powder provides 50g carbohydrate, this should be made up in 600-750ml water.

3. Trial hydration and fuelling strategies to work out what concentration of carbohydrate is right for you. This will depend on lots of factors such as whether you are male or female, sporting modality, and intensity and duration of the session. General recommendations are to consume between 0.8-1.0g carbohydrate/kg of body weight per hour during an event. It is also important to consume sodium to aid in the absorption of carbohydrate.

4. Choose the right supplements. When having sport supplements to fuel (gels, bars, sport drinks) choose a product that contains multiple transportable carbohydrate e.g. glucose and fructose, as opposed to a single sugar. This can be found in the ingredients list on the back of the packet. This will increase the rate at which your body can absorb the product because the two different carbohydrates are using different absorption pathways.

5. Have a balanced meal 3-4 hours prior to exercise; an example could include a chicken and salad wrap or 2 pieces of toast with peanut butter. Then consume a small carbohydrate dense snack 1-2 hours prior, like a piece of fruit or a muesli bar. This will provide you will an adequate amount of carbohydrate to fuel for your event but will minimise the risk of GI upset. It’s a great idea to trial pre-exercise meals and snacks to make sure you can tolerate your selections.

6. Don’t eat high fibre or high fat foods close to your session. Meals prior to exercise should be high in carbohydrate, low in fat and fibre and contain moderate protein. Common foods that cause upset include; bran cereals, legumes, caffeine and cruciferous vegetables. Include a small bowl of fried rice, porridge with banana, a fruit smoothie or a chicken and salad sandwich.

7. Seek advice from and Accredited Sports Dietitian. If you are diagnosed with IBS/lactose intolerance or gluten sensitivity, work with your Sports Dietitian to find out your triggers. These triggers should be completely removed from your diet prior to exercise and competition. If you have actively worked on the above and no improvement is seen, see a GP to test for gut related medical conditions.

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