Long runs are a staple in almost every run training plan. As most runners know, long runs are not just about running for a long time. How you fuel on long runs contributes to how well they go – and how good you feel running longer distances in marathon and half marathon training.
The Science of Fueling for Long Runs
During a long run, your body uses aerobic metabolism to produce energy. Aerobic metabolism relies on oxygen, carbohydrates, and lipids (fats). You get oxygen from breathing. Your body has robust fat stores, but these only account for a fraction of aerobic metabolism. A majority of the energy comes from carbohydrates, which are not easily stored.
Even if you ate before you ran, your body will likely have enough glycogen stored for 1.5 to 2 hours of running. (Not sure what to eat before you run? Start here!) You want to start supplying your body with easily available carbohydrates before it depletes those glycogen stores. You will have more energy, avoid that dreaded bonk, and perform better when you take in carbohydrates during runs longer than 80-90 minutes in duration.
A 2022 review published in Sports Medicine quantifies carbohydrate needs based on session duration and intensity. For runs at a low intensity (i.e. easy pace) and lasting over 90 minutes, the carbohydrate needs are classified as “moderate to high.” If any intensity at marathon pace or above is included, carbohydrate needs are “high.”
Fueling on long runs allows you to complete those long runs – without slowing down, feeling like garbage, or spending the rest of the day on the sofa. Fueling for long runs involves eating carbs (often sport nutrition products) to provide easily available energy.
When you eat carbohydrates during exercise, your gastrointestinal tract converts those carbohydrates into glucose. Your body takes that glucose from your bloodstream and sends it to your working muscles. In the working muscles, glucose is used as part of fast or slow glycolysis to produce ATP – which your muscle use for energy. Your body uses that glucose first; while it’s still burning glycogen, it’s not burning as much. This glycogen-sparing effect means you are significantly less likely to hit the wall and slow down.
How Fueling for Long Runs Impacts Recovery
The benefits of fueling for long runs are not limited to during the long runs themselves. Fueling actually helps your body recover more quickly from the long runs. You can function for the rest of the day and continue your training in the following days.
Why is this? During endurance exercise, a small amount of energy contribution comes from protein. The body takes stored protein (muscle protein) and puts it through a process called gluconeogenesis. This inefficient process converts the protein into carbohydrate, which then enters the Krebs cycle. However, the process also leads to higher amounts of muscle breakdown.
When you experience higher amounts of muscle breakdown, your body needs more time and energy to repair those muscles. Long runs already cause a significant amount of muscle damage, due to the prolonged duration of muscle contraction and mechanical tension. But because of the protein-sparing effect of fueling on long runs, your injury risk goes down and your recovery is quicker. Plus, you likely will have more energy – and not spend all day on the sofa.
Fueling for Long Runs Trains the Gut for Race Day
Another advantage of fueling for long runs is gut training. Gut training is the practice of consuming gradually larger amounts of carbohydrates during exercise, with the end goal of a faster gastric emptying rate and better tolerance to in-exercise feeding. As discussed in a 2023 review in Sports Medicine, repeat carb intake on long runs reduces gastrointestinal symptoms such as reflux, nausea, and stomach discomfort. If you fuel your long runs, over time your gut tolerates it better – which leads to lower outcomes of GI upset on race day.
How Much Fuel Should I Take on Long Runs?
According to a 2019 journal article in the International Journal of Sport Nutrition and Exercise Metabolism, the recommended intake during long runs is dependent on the time. For long runs of 1.5-2.5 hours, the recommended intake is 30-60 grams of carbohydrate per hour. For long runs over 2.5 hours, the recommendation increases to 60-90 grams of carb per hour. (It’s worth noting that the above-cited 2022 review found insufficient evidence for >90 grams of carb per hour).
How do you get to 60 grams of carbs per hour?
- Two high-carb gels (SIS Beta, PF 30, or Neversecond – all 30 g CHO/serving)
- One serving of Maurten 360 or Skratch Super High-Carb
- Three GU or Huma gels per hour
- Two Maurten gels plus Skratch Sports Drink
There is no perfect approach. Your exact strategy may vary based on your preferences, gut tolerances, and even exercise intensity. (You may find you like chews during a long run but use gels or sports drink in races, for example.)
What Should I Use for Fuel?
An ideal running fuel is high in easily digestible carbohydrates and low in fiber, fat, and protein. Most likely, your running fuel will have sugar in it. Sugar is not evil; it is an easily transportable source for energy production during exercise. Running fuel can be liquid, solid, or semisolid. There are dozens of options out there, so experiment to find what you enjoy eating during your runs. Options include:
If it seems like a lot, there are creative ways to carry your fuel with you!
How Much Does Fueling Impact Performance?
Significantly! A 2014 study published in the International Journal of Sports Nutrition and Exercise Metabolism compared runners who fueled freely during the Copenhagen Marathon with those who consumed 60g of carbs per hour. The runners were of equivalent fitness, yet those who fueled with 60 g of carbs per hour completed the marathon an average of 11 minutes faster.
Of course, you aren’t aiming for PRs in your normal weekly long run. However, fueling on your long run still aids in performance. Carbohydrate intake during long runs thus delays neuromuscular fatigue, enhances muscle function, and improves your work capacity. What that practically means: you can run for longer, without slowing down. You can log those long miles without slowing down or struggling to finish.
Don’t Forget Fluids & Electrolytes
Replenishing fluids and electrolytes is vital on long runs! Amongst other reasons, dehydration increases GI upset, so you want to minimize dehydration. For more on electrolytes on long runs, reference this article.
Listen to this episode of the Tread Lightly Podcast for an in-depth discussion on long run fueling!