Fuel Your Long Run

Carbohydrate intake during exercise

My first road running race was a Thanksgiving Day 5 km.  It was so simple.  Show up, run, go home, eat turkey.  And then came my first marathon.  So incredibly naïve, I was wondering why there was food at the aid stations, and most of the competitors were carrying gels.  Too scared to try anything new on race day, I ran until I bonked at just over the 2-hour mark.  I’ve come a long way since those days, and I now know carbohydrate intake during endurance exercise can greatly improve your performance.  So, what do you need to know?

  1. Do I need to eat during exercise?

If less than 60 – 75 minutes the research suggests no.

If longer than 75 minutes, yes.

 

2. Why do I need to eat?

You have limited stores of carbohydrate in your body, primarily in the muscle and liver.  Eating exogenous carbohydrate prevents hypoglycemia, maintains the necessary rate of carbohydrate oxidation for your exercise session, and improves endurance capacity and performance (Jeukendrup, 2014).

The higher the intensity and the longer the duration, the more carbohydrates per hour you will need to take in.

 

3. What should I eat?

Not all carbohydrates are the same.  The rate of carbohydrate oxidation is limited by how much carbohydrate your intestine can move to your bloodstream.  Transporters located in the intestine help move carbohydrate to the bloodstream.  Glucose uses a transporter called SGLT1.  These transporters are like toll booths in a highway. They can get fully occupied and not be able to transport any more glucose.  This happens at ~ 60 grams of glucose per hour.  Fructose, on the other hand, uses a different transporter, and allows for more carbohydrate to be moved to the bloodstream, up to ~ 90 grams per hour.  Drinks and foods that have a combination of glucose and fructose are ideal.

A few examples of energy products that contain a combination of carbohydrate sources include:

 

4. How much should I eat?

The figure below provides a guideline for the recommended amount of carbohydrate to take in depending on exercise duration.  It is incredibly important to practice your nutrition plan in training.  Physiological variability is huge, and you should find out the amount that your GI system can tolerate and what products work best for you.

Figure adapted from Jeukendrup, A (2014). A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise.

 

Reference:

Jeukendrup, A. A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. Sports Med 44, 25–33 (2014). https://doi.org/10.1007/s40279-014-0148-z

 

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