Elite Marathoners Are Fueling with 120g+ of Carbs per Hour. Should You?

New research shows higher carb intake can improve running efficiency, but it’s not a one-size-fits-all strategy.

For decades, marathon fueling advice has centered on taking in under 60 grams of carbohydrates per hour. But as cyclists have started pushing their carb intake above 120 grams per hour, runners have begun to question whether there is a benefit to doing the same.

A recent study in the Journal of Applied Physiology explored what happens when runners consume significantly more carbohydrates during marathon-intensity running and found that higher intake rates may allow athletes to use fuel more efficiently and run at the same pace with less metabolic cost.

Inside the Study: Testing the Limits of Carb Intake

To test this, researchers recruited eight elite male marathon runners (around 2:20 marathoners) and had them complete multiple long treadmill runs while consuming different amounts of carbohydrates per hour: 60 g, 90 g, and 120 g. The goal wasn’t to see who ran faster that day, but to understand what was happening inside the body. How much fuel they could actually use, how hard the running felt metabolically, and whether higher carb intakes improved efficiency.

Each runner completed three separate lab sessions, each lasting about two hours of steady running at marathon-like intensity. The only thing that changed between sessions was how many carbs they consumed per hour. The drinks were carefully designed using different blends of glucose and fructose to maximize absorption.

The researchers used advanced techniques (including labeled carbohydrates and oxygen measurements) to track:

• How much of the ingested fuel the runners were actually burning

• Total carbohydrate use

• How much oxygen did it take to maintain the pace (a measure of running economy)

• Gastrointestinal symptoms

  
  

This allowed them to see not just what the runners drank, but what their bodies truly used.

What Happens When Runners Go Big on Carbs

The big takeaway was that more carbs led to more carbs being used, and more efficiently.

As carb intake increased from 60 → 90 → 120 g per hour:

• Runners burned more carbohydrate overall

• A greater percentage of that fuel came directly from what they were consuming, rather than from stored glycogen

• At 120 g per hour, runners used the most exogenous fuel and showed a small but meaningful improvement in running economy; they needed less oxygen to run at the same pace compared to the 60 g/hour condition

  
  

In endurance terms, that matters. Using less oxygen at a given pace means the effort is metabolically “cheaper,” which could help preserve energy late in a marathon when fatigue normally builds.

Even among elite runners, GI symptoms were more common at 120 g/hour—some athletes tolerated it well, while others didn’t. So while the body can use that much carbohydrate, not everyone’s gut is ready for it without targeted training. This reinforces the idea that high-carb fueling is a trainable skill, not an automatic benefit.

It’s also important to acknowledge the study’s limitations. It was conducted on a treadmill and measured performance over a two-hour workout—not an actual marathon, which is typically longer. Additionally, the study included only elite male runners, so the findings may not generalize to all athletes. In other words, the study points to a physiological advantage—not a guaranteed PR.

So, How Much Carbs Should You Take In?

Traditionally, marathon fueling advice hovered around 30–60 g of carbs per hour, later creeping toward 60–90 g/hour. This study adds strong evidence that well-trained runners can benefit metabolically from going higher, even up to 120 g/hour, if they can tolerate it.

For most runners, this doesn’t mean jumping straight to 120 g/hour on race day. Instead, it suggests:

• 60 g/hour may be a minimum, not an optimal ceiling

• 90 g/hour is a realistic and effective target for many. Higher intakes can help, but only with gradual gut training

This study supports a shift in how we think about marathon fueling. More carbs can improve efficiency and fuel availability, even at marathon pace, but the gut is often the limiting factor, not the muscles. The smartest takeaway for most runners isn’t “fuel like an elite tomorrow,” but rather: Train your fueling the same way you train your legs, progressively, intentionally, and individually.