What might be causing your GI issues during exercise?

GI distress can be one of the most frustrating and debilitating things to occur during exercise and is prevalent across all ranges of ability, with reports of up to 83% of athletes suffering from some form of GI distress symptoms. However, a few simple changes to your diet could remove these occurances.

Table of Contents

• 01 - Consuming too much glucose
• 02 - Concentration of the gel or drink
• 03 - Composition of the food
• 04 - Using pain relief medication
• Take home message

01 - Consuming too much glucose

This may seem like a strange reason for your gastrointestinal distress during exercise but actually there is some good evidence to support this. If you are consuming more than 60 g/hr of glucose either in the form of an energy gel, drink or bar then this may be the source of your problem. Early work by Jukendrup and colleagues established that the human GI tract can only take up a maximum of 1 g/min of glucose due to the limiting factors to the transport proteins on the surface of the intestines. Therefore, if you consume more than this it will just hang around in the gut and cause bloating, nausea etc.

If you need to consume more than this per hour then it is recommended that multiple transporter carbohydrates are used. By this we mean a mixture of fructose and glucose in the gel, drink or food. This is because fructose utilises a different transporter on the intestinal wall and therefore, we can consume a further 0.8 g/min of carbohydrate. However, these high intakes of > 60 g/hr of carbohydrate are usually reserved for events longer than 3 hrs, otherwise up to 60 g/hr is usually sufficient in most cases. If you do need to use these higher intakes then look for products that are batch tested for banned substances and provide a good blend of glucose and fructose, such as the Science in Sport Beta Fuel Range.

02 - Concentration of the gel or drink

For most people that consume some form of carbohydrate whilst exercising they will purchase it from a sports nutrition brand, test in training and see how they get on, in some instances people will make the cardinal sin of using it in competition without testing it or pick an untested one from the feed station during an event because they've run out of their own. The problem with this is two-fold, firstly the supplement may have too much glucose for you to tolerate as discussed in point 1 and secondly, the concentration of it may be too high and impair gastric emptying.

Gastric emptying is the process of passing the food or drink from the stomach into the small intestine and is affected by a number of factors. For example, duration and intensity of exercise, environmental temperatures as well as the volume of fluid or food consumed. However, one of the major factors that affects gastric emptying is the concentration of the solution. Work by Vist and Maughan showed that either water or a relatively low contentration of 20 g/L of glucose maintained high levels of gastric emptying. Yet, when this concentration increased to either 40 or 60 g/L, the rate at which the solution left the stomach was slowed.

03 - Composition of the food

If you undertake a diet that is high in fat and low in carbohydrate then there is a possibility that your gut is not 'trained' to deal with the volumes of carbohydrate passed through it in competition. As we discussed earlier the maximum rate of glucose absorption is 1 g/min, however, this value is determined from subjects who consumed a normal diet which typically had an abundance of carbohydrate in it. So if you do not consume much carbohydrate in the body then there is a likelihood that the number of SGLT-1 transporters that process glucose on the intestinal wall are going to be lower that in someone who consumes a carbohydrate rich diet.

04 - Using pain relief medication

Often athletes wake up with aches and pains from the day before and this only gets worse with age. As a result of this athletes will default to over the counter pain relief medication in the form of ibuprofen. However, ibuprofen is an NSAID which is great for suppressing inflammation and pain but can be extremely detrimental to your gut. A study by Gabriel et al. established that those who consumed an NSAID were 3 to 5 times more likely to develop upper GI distress, mucosal bleeding or perforation of the lining. This evidence is further supported by literature from van Wijck and colleagues who determined that ibuprofen aggrevates exercise-induced small intestinal injury and impairs gut barrier function.

Take home message

So as we have discussed there are many factors that can affect GI functioning during exercise and some considerations you need to make so that you are less likely to have any issues. However, if the above does not work for you then it may be that your gut needs to be trained to tolerate more carbohydrate of which this can be achieved in a number of ways, but we will discuss this in more detail in a future post.