When you’re gearing up for a half marathon, there’s a lot to think about—your training plan, pacing strategy, gear, and perhaps most importantly, how to fuel for the race.
For many runners, the half marathon represents a significant leap in distance from previous races like the 5K or 10K, and with that increase in mileage comes new challenges, including energy management.
While shorter races like the 10K often don’t require mid-race fueling, a half marathon is a different beast. Running 13.1 miles demands a more strategic approach to nutrition to ensure your muscles have the energy to carry you to the finish line without hitting “the wall.”
But is fueling during a half marathon always necessary? The answer depends on factors like your pace, estimated finish time, and individual physiology, but as a running coach, I am going to go with, almost always, yes!
In this guide, we’ll break down why fueling is important, how to determine if you need it, and the best practices for staying energized during your half marathon.
Should I Fuel During a Half Marathon?
Yes, most runners benefit from fueling during a half marathon with energy gels, sports drinks, or real foods high in carbohydrates.
The faster you run, the more carbohydrates you burn.
Marathon race pace is slower than half marathon race pace, which means that a greater percentage of the calories your body needs can actually be produced by burning fat.
Of course, you still mainly burn carbohydrates during a marathon, but the reliance on fat exceeds the more intense half-marathon pace.
This means your glycogen stores may only be adequate for 75-90 minutes at your half-marathon pace.
Thus, fueling during the race is a good idea if your projected half-marathon finish time is above 75 minutes. Most runners take more than 75 or even 90 minutes to finish a half marathon, so fueling is critical for almost everyone.
Running Level110k Times By Age And Ability – Running Level. (n.d.). Runninglevel.com. https://runninglevel.com/running-times/10k-times reports that the average half-marathon finish time is 1:43:33 for men and 2:00:12 for women.
The slower you are, the more important your half marathon fueling strategy becomes, as you will take more time to finish your half marathon.
Just because your running pace is slower doesn’t mean your effort level is any less than a more competitive runner, so even very slow runners may be burning primarily glycogen during the half marathon.
Why Should I Fuel for a Half Marathon?
Any time you run or perform physical activity, your muscles need energy to do the work required to sustain the exercise. This energy (in the form of ATP) is generated by oxidizing or burning fuel from the nutrition you’ve taken in.
The two primary forms of fuel for the muscles are carbohydrates and fats. Proteins provide some amount of energy during intense exercise, although the relative percentage is much less.
Fat is the primary fuel source for the muscles during low-intensity exercise, such as walking, yoga, or very slow jogging.
Even for the leanest runners, the body has enough stored fat to sustain several days of continuous running without consuming more calories.
Each pound of stored body fat provides about 3,500 calories of energy, so if you use a rough estimate of 100 calories per mile for the energy expenditure of running, each pound of fat can power 35 miles of running.
Therefore, you could theoretically run for several days on all the body fat you carry.
However, here’s where fueling for running comes into play: During vigorous exercise, such as running, the muscles rely primarily on carbohydrates to produce energy.
Unlike in the case of body fat, glycogen stores are in a relatively limited supply.
Carbohydrates that you take in through your diet are converted into glycogen,2Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243–259. https://doi.org/10.1093/nutrit/nuy001 a much larger molecule that is formed by synthesizing many simple sugar molecules together.
When you run, your muscles, brain, and heart quickly use the available blood sugar for energy, so the stored glycogen can be broken down into simple glucose molecules.
Your muscle cells (or other tissue) can then use the glucose to generate ATP to support your exercise.
The body has limited glycogen stores in the liver and skeletal muscles, and these reservoirs deplete even faster as the intensity of your exercise increases. This is because producing ATP by oxidizing fat is a much slower process than producing ATP by burning glycogen.
As a result, the faster you run, the more your muscles rely exclusively on carbohydrates for fuel rather than fats.
The more vigorous your exercise, the higher the energy requirements of your muscles (and the more calories you burn per minute).
Since oxidizing fat is a much slower process, the energy yield from burning a triglyceride (fat molecule) can’t keep pace with the energy demand of the muscles.
In other words, generating energy by burning fat is insufficient for the high demand of the muscles during high-intensity exercise.
According to the Academy of Nutrition and Dietetics,3How to Fuel Your Workout. (n.d.). Www.eatright.org. https://www.eatright.org/fitness/physical-activity/exercise-nutrition/how-to-fuel-your-workout an endurance-trained athlete can store up to 1,800 to 2,000 calories of fuel as glycogen in the muscles and liver, though smaller runners might store closer to 1,500 calories or so.
Depending on your body weight, size and running pace, this means that you might store enough glycogen to support about 90-120 minutes of running at your marathon race pace effort.
If you don’t take in additional carbohydrates during the race, you will deplete your glycogen stores and face the dreaded experience of “bonking” or “hitting the wall.”
This sensation of fatigue and a drastic slowing of your running pace is because once you are glycogen-depleted, your muscles have to shift to burning only fat for fuel, and as discussed, this is a much slower process.
Therefore, you are physiologically forced to slow down because the muscles aren’t getting enough energy fast enough to meet their needs.
By fueling with simple carbohydrates during your race, you provide a trickle of additional glucose so that you never deplete your glycogen stores and don’t have to fall back on oxidizing fat.
However, it’s important to distinguish that you are not burning more calories overall when running in a glycogen-depleted state; the source of those calories shifts to include a greater reliance on fat rather than carbohydrates.
How To Fuel For Your Half Marathon
When putting together your fueling strategy, you need to consider the following questions.
- What should I eat during a half marathon?
- When should I fuel during a half marathon?
As with most things related to running, your body is unique, and what may work best for you in terms of fueling for a half marathon may look quite different from what works best for another runner.
Trial and error is always the best way to determine what works, so make sure that you practice your fueling strategy in your long runs for a successful race.
In terms of what to eat, focus on simple carbohydrates. Energy gels, chews, sports drinks, and sports jelly beans work well.
If you prefer real food, consider dried fruit like raisins, dates, pineapple, or apricots. Fresh fruit like bananas or applesauce squeeze packets can also work well. Check out our list of whole-food alternatives to energy gels here.
You can consider real food options if chewing and swallowing while running is comfortable for you, but for many runners, energy gels are the way to go because it is the easiest to consume on the run, literally.
When it comes to eating, the rule of thumb is to stay ahead of your body’s carbohydrate needs, which means starting fueling at the 30-45 minute mark of the race. (I also always consume an energy gel about 20 minutes before my half marathon to get a kick before the start.)
To figure out how many grams of carbohydrates you should consume per hour, use the following equation:
Weight in kilos = grams of carbohydrates per hour
For example, if I weigh 60 kilos or 132 lbs., I will want to consume around 60 grams of carbs per hour. Each product is distinct but that works out to about two energy gels per hour.
Therefore, depending on your estimated half marathon finishing time, you can calculate how much you would need for the entire race.
If I plan to run the half in two hours, I can expect to take 3-4 gels with me.
The most important thing you can do regarding your half marathon fueling plan is practice, practice, practice.
During your long runs, experiment with and test different fueling strategies, products, and timing to really nail down your routine.
Another important thing to consider is how you will carry your fueling with you on the race day. Will you use a water bottle, hydration pack, pockets, or flip belt, or will you just use the aid stations provided by the organization?
If you decide to use the organization’s aid stations, ensure you know what type of hydration and nutrition they plan to provide and if it works with what you have been using during training. You don’t want any unwanted tummy trouble because you tried a new energy gel brand at the race.
If you are unsure how many calories you should consume to support your training, you can speak with a sports nutritionist to guide you.
Now that we have race strategy nutrition worked out, here are some great ideas for your next pre-race meal or pre-race breakfast:
Interesting article – I just ran a half marathon Sunday and because of my estimated pace, I chose no nutrition or water the entire race. I felt it in the last 300m but finished very well. I knew I could because of my marathon training but was running about 1min/mi faster than marathon pace. I do take UCAN every 3 miles during a marathon but will have to consider doing one or two in my next half.