90 Grams of Carbs an Hour: The Fueling Rule Rewriting Marathon Times

For three decades, marathon fuelling advice sounded the same. Thirty to sixty grams of carbs per hour. More than that and the stomach rebels.

That number is now outdated. Elite marathoners routinely take 90 grams per hour.

Some are experimenting with 120. And new research suggests the body can genuinely use it.

The question is no longer whether to fuel bigger. It is how much is right for you, and how to train the gut to tolerate it.

What the New Research Actually Found

A recent study tested eight elite male marathoners under three fuelling conditions during 2-hour treadmill runs: 60, 90, and 120 grams of carbs per hour.

The headline finding: at 120 grams per hour, oxygen cost at marathon pace dropped by 2.6 percent compared to 60 grams per hour.

For a 2:10 marathoner, that efficiency gain translates to measurable time off a personal best.

For a 3:30 marathoner, the arithmetic is less clean but the direction is the same.

The GI trade-off

The study also found the obvious catch. Every runner reported at least one moderate or severe GI symptom in every condition, but severity and frequency were highest at 120 grams per hour.

More fuel is not free. The gut has limits, and pushing those limits without training first ends in a very specific race-day disaster.

Why the Old 60-Gram Ceiling Existed

The 60 gram ceiling came from research on single-source carbohydrates, usually glucose or maltodextrin. The limiting factor was intestinal transporter saturation.

The SGLT1 transporter that moves glucose from gut to bloodstream maxes out around 60 grams per hour.

The breakthrough was mixing carbohydrate sources.

Fructose uses a different transporter (GLUT5), which runs in parallel. A glucose plus fructose blend at roughly a 2:1 ratio clears the 60 gram ceiling cleanly.

This is why modern sports drinks and gels list two carbohydrate sources, not one.

Read the label on any high-carb gel sold in 2026 and the mix is deliberate.

What This Means for Different Runners

Elite and sub-elite marathoners

The target is 90 to 120 grams per hour, assuming months of gut training.

The efficiency gains are real, the research is strong, and the top of the sport has already shifted.

Recreational marathoners (3:30 to 4:30 finishers)

The target is 60 to 90 grams per hour. This is the sweet spot where performance improvement is substantial and GI distress stays manageable with proper training.

First-time marathoners

Start at 30 to 60 grams per hour. The priority is finishing without a GI disaster, not optimising a time.

More can be added once the first marathon is in the bank.

Half-marathoners and shorter

Below 90 minutes of continuous running, glycogen stores alone can usually carry the effort.

A single gel at the start or around the hour mark is enough.

The Fueling Products That Actually Deliver It

Hitting 90 grams per hour is harder than it sounds. Most standard gels contain 20 to 25 grams of carbs each. That is 3 to 4 gels per hour, which is a lot of packets, a lot of water, and a lot of chewing while trying to breathe.

• High-carb gels now routinely pack 40 grams per pouch, so two per hour hits 80.
• High-carb drink mixes deliver 60 to 90 grams per 500 ml bottle.
• Combining a drink mix with one gel every 30 minutes clears 90 grams reliably.

For a deeper breakdown on specific products, see our guide to the best energy gels for runners.

The Gut Training Reality

The number on the plan is useless if the gut cannot process it. Jumping from 40 grams per hour to 90 grams per hour the week before a race is a near-guarantee of a GI meltdown somewhere between mile 15 and mile 20.

The gut adapts the way the muscles do, through progressive overload. Start where you currently fuel.

Add 10 grams per hour on every third long run. By week 12 of a build, 90 grams should feel routine.

This is covered in detail in our guide to fluids, carbs, and salt in a marathon.

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A Simple 90-Gram Protocol

For a 3:30 to 4:30 marathoner who has done basic gut training:

• Pre-race: 90 to 120 grams of carbs 2 to 3 hours before the gun.
• Mile 3: First gel (25 grams) with water.
• Mile 6: Sports drink refill at aid station (approximately 25 grams per 500 ml).
• Mile 9: Second gel (25 grams).
• Mile 12: Sports drink (approximately 25 grams).
• Continue the gel/drink alternation every 2 to 3 miles through mile 24.

Running the numbers, this clears 80 to 95 grams per hour for a 4-hour finisher.

The Takeaway

The old 60 gram ceiling was never a physiological limit. It was a product limitation that stopped being true a decade ago.

Elite marathoners already know this. Recreational runners are catching up.

The authoritative sports science literature now supports 90 to 120 grams per hour as the frontier of what the trained gut can process (see the NIH analysis of exogenous carbohydrate ingestion).

The constraint is no longer physiology. It is training the gut to meet it.