Trail runners fuel up on the Trail de la Sainte Victoire 2011 in Bouches-du-Rhone, France/Photo by akunamatata


Most endurance athletes have experienced what is known as exercise-related gastro intestinal (GI) distress at some point and time. Most frequently experienced on race day (as athletes attempt to meet the fueling demands of competition), exercise-related GI distress can be caused by a number of factors: foods eaten in the several days prior to or during the competition, dehydration, consuming too much fluid at once, and not adequately training the stomach to handle what will happen on race day. Every person is unique, but there are some key steps you can take to help avoid GI distress and fuel yourself to the finish line.

Step 1: Eat low residue foods in the two to three days leading up to competition.

Based on their fiber content, foods can be categorized as either high or low residue. The higher the residue, the more fiber the food contains. While a high fiber diet is preferable for daily good health, the use of low residue foods in the days leading up to competition can help to minimize GI distress. This can be accomplished by switching out high fiber foods like whole wheat bread, quinoa, and apples for ones with reduced fiber content—such as white bread, low fiber pasta, and plums.

Step 2: Consume your race-day fuel with fluids.

With all of the gels, shots, and bars on the market a common mistake competitors make is not consuming enough fluid on race day to help digest all the carbohydrates. The more dehydrated you become the harder it is to empty carbohydrates from the stomach; for every 15 to 20 grams of carbohydrates consumed, an athlete should drink at least six ounces of fluid. Some achieve this by just consuming carbohydrates as fluids while those using more solid forms (such as gels or shot blocks) go for the water offered on course. Be careful though that you don’t overdue fluid consumption. Another key aspect to avoiding GI distress is how much you drink at any one time. Consuming large volumes of fluid can lead to stomach distension and GI distress because the stomach cannot empty large amounts of fluids quickly. Gulping small volumes frequently can minimize these negative effects.

Photo by Nick Saltmarsh

White bread can help stave off distress/Nick Saltmarsh
Step 3: Choose your carbs wisely.

The type and amount of carbohydrates you consume will determine if it ever gets out of your stomach and reaches the muscles that so desperately need it mid-race. It’s currently recommended that athletes consume anywhere between 0.5 and 2.0 grams of carbohydrate per minute, although the goal for most athletes will be to take in between 1.0 and 1.5 grams per minute.

Carbohydrates come in many different forms including simple sugars like glucose, sucrose, and fructose, and complex ones like maltodextrin, waxiy maize, and super starch. Depending on the amount of carbohydrate you want to consume will determine the type of carbohydrate you use. Consuming only 0.5 grams per minute can be done with simple sugars, although in long races this may not provide enough carbohydrate and athletes may “bonk;” consuming a more complex carbohydrate will help to minimize this risk. Complex carbohydrate consumption allows athletes to consume from 0.5 grams into the more ideal range of 1.0 to 1.5 grams per minute.

How does this all work, exactly? Due to their lower osmolality, complex carbs like the ones listed above can be consumed in higher concentrations. (Osmolality is the concentration of particles in a volume of fluid. The lower a carbohydrate’s osmolality, the more we can consume and the faster it can be transported out of the stomach and delivered to the working muscles.) High concentrations of simple sugars, such as fructose or glucose, produce a high osmolality and as a result struggle to get out of the stomach when consumed in large amounts. This struggle is what most people feel when they experience cramping, bloating and discomfort during a race. Superstarch and waixy maize have the lowest osmolality, but also confer an additional advantage over maltodextrins—something known as a high molecular weight. Carbohydrates with a high molecular weight move out of the stomach much easier and thus reduce the chance for GI distress even more so than maltodextrins.

Step 4: Electrolytes.

Many athletes attempt to hydrate prior to and during competition with drinks that have too few electrolytes. Electrolytes are the “drivers” in the body that make muscles contract and help drive fluid out of the stomach. Athletes can ensure good hydration in the days leading up to the race by adding electrolyte tablets to water or consuming an electrolyte beverage. On race day, making sure the electrolytes consumed have 75 to 100mg of sodium for every 4 ounces of fluid will give most athletes what they need to empty fluid from the stomach and help stave off muscle cramps. Salty sweaters or those prone to cramping may choose to take on up to 200mg of sodium and/or salt their foods heavily in the days prior to competition.

Step 5: Practice makes perfect!

Did you know that just like your muscles, your stomach and intestines can be trained to handle higher volumes of fluid and higher concentrations of carbohydrates? This is best achieved by practicing your race day fueling strategy at least three to four times prior to competition and consuming fluids regularly in training.


Krista Austin is a physiologist and nutritionist who consults for the Nike Oregon Project, numerous track and field athletes, USA Triathlon, among others. She’s worked as a physiologist for the U.S. Olympic Committee and as a performance nutritionist for the English Institute of Sport and England’s Cricket Team. She has a PhD in exercise physiology and sports nutrition, a master’s degree in exercise physiology, and is a Certified Strength and Conditioning Specialist. Visit her online at