Gut Training for Fueling and Performance

The Gut Challenge with High Carbohydrate Fueling

With the high carbohydrate fueling revolution well underway in the endurance sport community, many who are new to high carb fueling may be unsure about where to start. We are often asked “how do I prepare my body for fueling?” or  “what do I fuel with?” . With high carb intakes being discussed in the media and among friends, some caution should be taken with consuming these high amounts of carbs (90+ grams per hour), especially if you are new to high carb fueling. 

Just as you would approach training your body for a big event, you should train your gastrointestinal (GI) tract or gut to handle these high intakes of carbs. The outcome is most likely unfavorable if you attempt to consume 90+ grams of carbs per hour, especially if high carb fueling is new to you. 

It is thought that GI discomfort and distress may be due to a combination of factors such as the heat, dehydration, unusually high carb intake (for that individual), high intensity exercise, etc. Despite GI sensitivity being variable among different individuals, training your gut to handle these high amounts of carbs per hour will greatly reduce the chances of experiencing future discomfort during key events. 

So what is the scientific evidence for gut training and fueling for performance? 

The Science

While there is limited research that examines training the gut for high carb intake during exercise, it is highly recommended by sport scientists and practitioners to practice your race fueling strategy during your training session. Regardless, the current scientific evidence appears to suggest that the gut is highly adaptable.

It is known that the GI tract is highly adaptable to diet and the transport of nutrients from the GI tract into the body. There are studies (Cunningham et al. and Horowitz et al.) that suggest increasing the amounts of carbs consumed in one's diet can increase the rate at which glucose is emptied from the stomach into the small intestine. Additionally, another study suggests that increased dietary fructose can increase the rate of gastric emptying of fructose. It appears that these adaptations can occur as rapidly as three days of diet manipulation. The proposed explanations of these adaptations are: 1) the specific receptors for carbs have reduced sensitization and 2) a neural component where there is a reduced inhibition of gastric emptying. However, to be clear, gastric emptying is not the limiting factor related to the absorption of carbs into the body, rather it is the limited capacity of specific transporters in the small intestine to absorb and transport carbs into the blood. 

Once in the small intestine, carbs are moved from the small intestine to inside the body through specific transporters. The specific transporter for glucose is called the sodium-dependent glucose transporter (SGLT)-1. The specific transporter for fructose is called glucose transporter (GLUT)-5. It is widely accepted that the SGLT-1 can transport up to 60 grams per hour. The total amount of carbs absorbed per hour can be further increased with the consumption of fructose, which has been shown to increase the absorption rate to above 60 grams per hour. Thus, it is likely that some of the contribution of GI distress could be due to excess and unabsorbed carbs in the small intestine, which may lead to bloating due to osmotic shifts. 

While the data is limited, gut training in humans has been proposed to increase the number of SGLT1 transporters and may be the primary way in which more carbs can be absorbed with gut training. This may support the anecdotal evidence of carb ingestion rates greater than 120 grams per hour and evidence in the scientific literature. 

Recommendations

With the science briefly discussed above, we suggest the following to help reduce the chances of gut distress during your events and competition: 

• If you are new or unfamiliar with fueling during your training or racing, we suggest starting with a lower target carb intake per hour. Between 40-60 grams of carbs per hour is a reasonable target to begin with. This is equivalent to just one Carbs Fuel 50g Original gel per hour. As you become comfortable consuming this amount and are finding that you are not experiencing any GI discomfort, you can begin increasing the amount of carbs consumed per hour. 

• Make sure to train with or test the products that you plan to use during competition. This is to ensure that your GI tract agrees with the fueling product and the ingredients used. The Carbs Fuel Original 50g Energy Gel does not use preservative or gelling agents, which helps to decrease the probability of GI discomfort. 

• Experiment with different carb forms and the combination that meets your fueling needs. This includes using a combination of gels, drink mixes, and solid foods in varying amounts. In doing so, you can test different fueling strategies to help you succeed during event/competition day.

• When training and competing in hot weather, ensure to consume ample amounts of water, in addition to your fueling products, to help minimize the chance of GI distress.

• Spend time practicing fueling during higher training intensities, such as tempo or race pace  workouts, to see how your body reacts to fueling during high intensity exercise.