You educated for months, confirmed up prepared, and someplace round mile 18 your legs turned to concrete and also you had nothing left.
For many runners, the race isn’t misplaced in coaching.
It’s misplaced within the gasoline plan.
A 2025 examine discovered that the common marathoner takes in simply 21.7 grams of carbohydrates per hour throughout a race [1], whereas present pointers from sports activities scientist Dr. Asker Jeukendrup suggest 60–90 grams per hour for occasions lasting greater than two hours [2].
That’s not a small hole.
That’s most runners working on fumes for the second half of their race whereas believing they’re fueling effective.
Right here’s what the analysis really says, and construct a plan that holds up on race day.
Why Your Physique Runs Out of Gasoline (And When)
Consider your muscle groups like a automobile with a small gasoline tank.
Your physique can retailer roughly 90 minutes value of glycogen at marathon race tempo.
After that, with out exogenous gasoline, your engine begins sputtering, blood glucose drops, tempo slows, and the wall arrives whether or not you invited it or not.
The explanation most runners hit the wall is easy: they began fueling too late, too little, or by no means.
Fueling isn’t elective upkeep.
It’s the race itself.
The Carbohydrate Math You Must Know
For a 4-hour marathoner, the present suggestions translate to roughly 240–360 grams of whole carbohydrates throughout the race, roughly 6–9 customary gels.
Most runners take 3.
The ceiling on how a lot carbohydrate your physique can take up comes right down to intestinal transport.
Glucose makes use of a transporter known as SGLT1, which maxes out at round 60 grams per hour.
However Dr. Jeukendrup’s analysis demonstrated that including fructose alongside glucose unlocks a second transporter, GLUT5, and pushes absorption charges to 90 grams per hour or extra when mixed in a 2:1 glucose-to-fructose ratio [3].
Merely put: in case your gels solely include glucose or maltodextrin, you’re capped at 60 grams per hour regardless of what number of you are taking.
If you wish to gasoline above that threshold with out GI misery, you want a dual-source product.
Verify your labels.
Gels vs. Chews vs. Actual Meals — What the Analysis Truly Exhibits
Right here’s one thing that may shock you: the format of your gasoline issues lower than you assume.
A 2025 evaluation confirmed that gel, chew, and liquid codecs produce broadly comparable oxidation charges when the carbohydrate dose and kind are matched [4].
The format isn’t the limiting issue.
The limiting issue is whether or not you’re hitting your carbohydrate targets with the proper sort of carbs.
That mentioned, every format has sensible trade-offs value understanding.
Gels are probably the most studied and best to eat at race tempo, exact, moveable, and fast-absorbing. The principle draw back is taste fatigue over a four-hour race.
Chews provide extra of an consuming expertise and work nicely within the early miles when chewing is manageable. They’re slower to eat and require a number of items to match one gel’s carbohydrate load, one thing to think about once you’re pushing laborious at mile 22.
Actual meals bananas, raisins, dates, is authentic gasoline. Analysis discovered potato ingestion produced equal time-trial efficiency to business gels [5], however you’d want 128.5 grams of potato to match 23 grams of gel. That quantity will increase GI discomfort, and the street marathon logistics are apparent.
The underside line?
Use gels as your main gasoline supply, combine in chews for selection within the early miles, and deal with actual meals as a welcome shock at support stations, not your main technique.
GI Misery: Why It Occurs and Find out how to Forestall It
Between 20–57% of marathon runners report a minimum of one GI symptom throughout a race, nausea, cramping, bloating, or worse.
That statistic isn’t inevitable.
Throughout intense train, blood is redirected away from the digestive system to your working muscle groups, which suggests your intestine is performing at lowered capability exactly once you’re asking it to course of gels each 20 minutes.
Add concentrated sugar with out sufficient water, or take a gel and a sports activities drink concurrently on the similar support station, and also you’ve created an osmotic mess your intestine can’t deal with.
The most typical preventable mistake is taking gels with out water.
Gels want fluid to dilute osmolality within the intestine, by no means wash them down with sports activities drink, since you’re stacking two concentrated carbohydrate sources without delay.
The second most typical mistake: making an attempt one thing new on race day.
For those who haven’t practiced with it in coaching, don’t contact it on the course.
And begin fueling early, by mile 4 or 5, earlier than you’re feeling any vitality drop.
By the point you’re feeling depleted, it’s already too late to completely reverse it.
Coaching Your Intestine Is Not Non-obligatory
Right here’s the excellent news: your intestine is trainable.
Dr. Jeukendrup’s intestine coaching analysis exhibits that constantly consuming carbohydrates throughout train stimulates your gut to upregulate the transporters , SGLT1 and GLUT5 , liable for absorption [6].
One examine discovered that intestine coaching can cut back GI signs by 26–47% and enhance carbohydrate absorption by 45–54% [7].
The protocol is easier than it sounds.
On each long term of 90 minutes or extra, apply fueling together with your goal race product at your goal race dose.
For those who’re at the moment comfy at 30 grams per hour, bump it to 40 in your subsequent long term.
Construct towards 60 grams per hour minimal over 8–12 weeks earlier than your race.
You’ll tolerate some discomfort in coaching , gentle bloating, a little bit of fullness , whereas your intestine adapts.
That gentle coaching discomfort is much better than a mid-race GI catastrophe.
Don’t Overlook Electrolytes
Carbohydrates get a lot of the consideration, however sodium is the electrolyte you lose on the highest price by means of sweat, and most runners aren’t changing almost sufficient.
A 2025 examine discovered the common marathon runner consumed solely 192 mg of sodium per hour, whereas the American Faculty of Sports activities Drugs recommends 300–600 mg per hour for occasions over two hours [8].
The chance isn’t simply cramping.
A landmark NEJM examine of the 2002 Boston Marathon discovered hyponatremia, harmful low blood sodium, in 13% of finishers, prompted not by sodium loss however by consuming extreme plain water with out changing electrolytes [9].
The repair is easy: select gels with sodium, carry electrolyte capsules, or use sports activities drink at support stations for supplemental assist, particularly within the again half of the race.
For those who recurrently see white residue in your pores and skin or clothes after lengthy runs, you’re probably a salty sweater and will goal the upper finish of these suggestions.
Constructing Your Personalised Plan
The science provides you the framework.
Your lengthy runs provide the reply.
Begin with a goal of 45–60 grams of carbohydrates per hour, select a dual-source gel as your main product, and apply on each long term.
Take a look at completely different merchandise. Notice how your abdomen responds. Regulate the dose, alter the timing, maintain notes.
The runner who nails marathon fueling isn’t the one who discovered the right gel.
It’s the one who confirmed as much as the beginning line with a plan they’d already practiced sufficient instances to belief.