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Fueling Your Long Run

Photo of a veggie bowl, bread, piece of fruit, and a spoon with spices. One the right hand of the photo is a title, food is fuel.

Background and Practical Tips for Nutrition on Long Runs

This blog was written as part of our partnership with Ultra Trail Drakensberg.  As a coach partner, we offer tips on training and racing for athletes.  The race offers distances between 21 km – 160 km in the beautiful Drakensberg mountain range in South Africa.

There are certain aspects of sports performance where you can greatly improve performance without doing any additional training.  Things like sleep, stress management, and nutrition are all examples that contribute to training and racing at your best.  When you fuel properly for long runs, it not only improves your performance on the day but can also help aid in your recovery after the run.  Below we go over some background behind fuelling during exercise as well as some practical tips:


1.  Do I need to eat during exercise?

If your training session is less than 60 – 75 minutes the research suggests it is not imperative that you fuel during the session (Jeukendrup, 2014).  Interestingly however, research studies have found a performance benefit at shorter exercise durations from simply doing a mouth rinse with a carbohydrate drink (Jeukendrup, 2010).   If you are heading out in the morning for a training session fasted, it’s important to understand that after the session you are now in a caloric deficit and will need to fuel well after the session to ensure you adequately replace your caloric expenditure.  For time-pressed athletes, it may be helpful to fuel before or during shorter morning training sessions to lessen the time spent eating a larger breakfast.

If your training session is longer than 75 – 90 minutes, research recommends that athletes fuel while training (Jeukendrup, 2014; Tiller, 2019).


2.  Why do I need to eat?

You have limited stores of carbohydrate in your body, primarily in the muscle and liver.  Taking in carbohydrate during a training session or race 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.  Athletes also utilize free fatty acids as fuel particularly at lower relative intensities.  Your body will also start to utilize more fat as a fuel source when glycogen stores start to get low (Waskiewicz, 2012).  However, even at lower intensities carbohydrates are oxidized as well and at extremes of temperature and altitude the rate of carbohydrate oxidation will increase (Jeukendrup, 2003).


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 approximately 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 approximately 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?

When racing events that will take 75 minutes or longer, your performance will benefit from taking in energy.  The maximum amount of carbohydrate that your intestine can absorb is approximately 90 grams per hour when coming from a combined glucose and fructose source.  An example of a good food source with combined glucose and fructose is a banana.

Research in ultra-endurance events has suggested a range of 30 – 90 grams of carbohydrate per hour (Thomas, 2016 ; Tiller, 2019).  Anecdotally, when I ask my athletes to practice a nutrition strategy on long runs most of them report around 45 grams of carb per hour without any direction from me.  However, each athlete needs to find where they best fall in that range.

Research has found caloric intakes of 150 – 400 kcal/hr and 5 – 10 grams of protein per hour to be beneficial at the ultramarathon distances (Tiller, 2019).


Practical Tips:

  • Experiment in training and record your results. Each athlete’s physiology is unique.  How tolerant our gastrointestinal system is in absorbing nutrients and tolerating various foods is highly variable.  The only way to know what works for you is to experiment in training.
  • Create a list of foods and drinks that you enjoyed and sat well with your tummy while out on long runs.
  • Write down the calories, grams of carbohydrate, fat, protein, and mg of electrolytes each food or drink contains. This will help with creating a feasible combination of food and drink per hour to hit your intake goal.
  • Context matters! Things like hydration level, ambient temperature, running intensity, and stress can all impact how well you tolerate certain foods and the amount of food and drink you can take in.  Runners who know what combination of food and drink work well for them in both hot and cold weather have a huge advantage.
  • Working with a registered sports dietician can be beneficial for any athlete, but particularly for athletes who struggle with GI distress or ones that have complex health histories such as an autoimmune disorder, anemia, bone stress injuries, or relative energy deficiency in sport (RED-S) to name a few.



Jeukendrup AE. Modulation of carbohydrate and fat utilization by diet, exercise and environment. Biochem Soc Trans. 2003;31(Pt 6):1270–3.

Jeukendrup, A. A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. Sports Med 44, 25–33 (2014).

Thomas, D. & Burke, Louise & Erdman, Kelly. (2016). Nutrition and Athletic Performance. medicine and science. 48. 543-568. 10.1249/MSS.0000000000000852.

Tiller, N.B., Roberts, J.D., Beasley, L. et al. International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr 16, 50 (2019).

Waskiewicz Z, Klapcinska B, Sadowska-Krepa E, Czuba M, Kempa K, Kimsa E, Gerasimuk D. Acute metabolic responses to a 24-h ultra-marathon race in male amateur runners. Eur J Appl Physiol. 2012;112(5):1679–88.

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