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BASICS OF ENDURANCE NUTRITION - Part 3, What about Race Day Race Day Gastrointestinal (GI) Distress!

The season has begun! Soon, if you haven’t already, you will be lining up your race schedule. The off season is now over, and where did it go? Did you achieve your off season goals? In this Part 3, I will cover a little about GI distress. You do not want to experience a "shart". What is this you ask? It might be better if you look it up in the urban dictionary.

GI distress, trust me it is certainly not something you ever want to experience race or not. There are many things that can ruin your race day experience and GI distress can be one of those things. I had this horrible experience during my very first Full Ironman. I honestly don’t recall how many stops I made during the run, there was a point in the run where I decided to break one of the golden rules because I was afraid of two things, not finishing, and dehydration. So, I took something to calm my stomach, it worked, although it didn’t kick in until the last 5 miles of the run.

According to a research study, more than 43% of triathletes reported serious gastrointestinal (GI) problems and 7% did not finish because of these problems. This study also showed a strong correlation between GI symptoms and having a history of GI symptoms. It is best to prevent problems by training the gut during training and having a tested race day nutrition plan (your coach should be able to provide you with guidance in a nutrition plan, but don’t wait till race day to get a nutrition plan, you want to test your nutrition during your training), – and a backup plan should issues arise. Symptoms vary among athletes, and can be classified as upper and lower GI tract problems. Main causes of GI distress:

  • Physiological (reduced blood flow to the gut) is the most common cause.

  • Mechanical - due to the bouncing effect of running

  • Nutritional - such as issue due to fructose, fiber, fat, protein and concentrated carbohydrate solutions, a lack of sodium, and dehydration.


Slow your pace and allow your stomach and intestinal symptom the opportunity to empty. When symptoms improve restart the fueling and hydration process with a sports drink. Once consumed, fluids must be absorbed through the intestines to be moved into the cells. Any factor that reduces gastric emptying time and intestinal absorption will negatively affect the athlete’s performance. Allow me to offer some some basic tips for gastric emptying and intestinal absorption:

Gastric Emptying

Gastric emptying is the rate of fluid and substrates out of the stomach. A major factor to speed gastric emptying involves maintaining a relatively high fluid volume in the stomach. However, concentrated fluids and fluids

with higher energy content decrease gastric emptying rate. Exercising intensity exceeding 75% of VO2max decreases emptying rate. Dehydration also decreases gastric emptying, and therefore increases the risk of gastrointestinal distress.

Intestinal Absorption

The absorption of water in the small intestines is dependent on the absorption of sodium. Therefore, low to moderate amounts of sodium increase intestinal fluid absorption. Fluids with less than 8% concentration of glucose also increase fluid absorption. This is equivalent to 8 grams of carbohydrate per 100 ml or approximately 7 grams/4 fluid ounces. The following factors affect intestinal absorption:

  • Higher volume of intake - INCREASES

  • Concentrated fluid - DECREASES

  • Increased energy content - DECREASES

  • Exercising > 75% intensity - DECREASES

  • Low to moderate level of sodium - INCREASES

  • Fluids with < 8% concentration glucose - INCREASES​

Electrolytes are also important, as your body cools itself through sweat, you will lose several key electrolytes, as well as effect the ability for intestinal absorption. Besides sodium, potassium, magnesium and calcium are also important electrolytes that are lost in sweat, below is what these electrolytes do to help your body function:

  • Potassium controls fluid and electrolyte balance, assists in the conduction of nerve transmission and helps move glucose into the cell.

  • Magnesium regulates muscle relaxation and aids electrolytes through the cell membranes.

  • Calcium plays a role in skeletal muscle contraction, nerve impulse transmission and the synthesis and breakdown of muscle and liver glycogen.

I always tell my athletes to experiment with different nutrition and electrolytes during their many hours of training. Be sure to log your nutrition during your training, take note of what you used, what worked and didn’t, and especially the serving size/amounts (when you find nutrition that works for you, you will want these notes so that you can replicate the mixtures and such for your race day). I would also suggest that they consider contacting the race director, or researching the race information to understand what race day nutrition will be provided, and to in fact train with that nutrition so that you can know better come race day whether or not the race day nutrition will agree with your body.

March has come in quickly, I am in fact preparing for the 2017 Boulder Ironman. Hope to see you out at some races. Or out on the trails.

Richard Nevarez

Ironman Certified Coach

FE26TriCoach, LLC

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