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Practice Makes Perfect: Nail Your Race-day Fueling

Updated: Feb 6, 2022

Odds are if someone were to ask you how your marathon training was going the conversation would most likely revolve around weekly mileage, tempo runs, long runs and perhaps cross training strength routines. While these aspects of training for a marathon are no doubt most important, there’s another part of marathon training that often gets underemphasized, something renowned sports nutrition scientist, Asker Jeukendrup refers to as training the gut. At its most basic level, training the gut means training your stomach to withstand the energy demands needed to complete a marathon without running out of fuel and free of GI issues.

Science has proved over and over that glycogen or carbohydrates are a marathoner’s number one fuel source. However your body only has the ability to store an estimated 1,800 to 2,000 calories of glycogen, enough fuel for about 90 to 120 minutes of rigorous running. So unless you plan on breaking the 2-hour marathon you’re going to take in fuel during the maratho

n. Recommendations on how much carbs you should take in vary greatly from 30g to 90g, making finding your optimal fueling intake somewhat of a blinded trial and error. However there are a few steps you can take over the next 7 weeks to narrow in on your best marathon day fueling strategy. Here’s what need to do:

Step One: The first step in nailing your race day fueling is figuring out what type of fuel you’ll use. Today’s market is flooded with more then enough products to choose from. In this post I’ve highlighted some of the top options. My suggestion is to go out to your local running store and try a bunch of them. Narrow in on two to four that you enjoy the taste.

Step Two: The next step is testing how your stomach will handle the fuel with GI issues being common when taking in fuel during exercise. Jeukendrup explains this could be due to reduced bloodflow to the GI during exercise effecting glycogen absorption rates. I recommend taking your favorite fueling option and using it at the beginning of a shorter run to test if you’ll have GI issues. This way if you do experience stomach issues you’re not dealing it with it as long as you would during a long run. If you have no issues during a shorter run try it during your next long run to further test. If you do experience issues, there could be a quite a few variables causing the issue (too much to discuss here), but I would suggest trying another type of fuel first.

Step Three: Once you find a fuel, you’ll want to work towards finding your race day intake levels and timing. Jeukendrup and colleague Bill Braun have developed an application called Fuel The Core to help determine how much carbs and hydration you should take in race day as well as the ideal timing throughout the marathon. Using key data such as projected finish time, weight, fueling preference and daily carb intake, Fuel The Core will give your optimal race day fueling. Go to to determine your race day fueling and hydration plan.

Step Four: Now that you have your target fueling and timing for race day, you’ll want to practice it during your weekly long runs. Over the next few weeks during your long run work up to taking in the total amount Fuel The Core suggested you do race day. Jeukendrup even suggests trying to exceed your race day carb intake during training to help prepare your stomach for the lower absorption rates come race day. This will decrease chances of experiencing GI issues on race day because you’ve trained your stomach to handle higher levels of carbs. He also recommends there is benefit in training without carbs, suggesting the mid-week long run as a perfect opportunity to train without taking in fuel.

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