Do You Need Gels for a Half Marathon? Yes. Here's the Science.

A coach recently posted on Threads that "most trained runners really should be able to go 13 miles on a flat course at sea level with no gels," adding that they once ran a 1:04 half marathon on just a few sips of water.

Cool. And I once drove from Denver to Albuquerque on a quarter tank of gas because I was too stubborn to stop. Doesn't mean it was a good idea, and I definitely wouldn't recommend it as a strategy.

Do you need gels for a half marathon? The short answer is: it depends on how long you're out there, and the research is pretty clear on what that means. This kind of advice, wrapped in the humble-brag of elite performance, is everywhere in endurance sports. The implication is clear: if you need fuel for a half marathon, you're somehow less tough, less trained, less legitimate as a runner. Real athletes just don't need to eat, I guess.

Let's talk about why this is both physiologically incomplete and culturally toxic. You can find even more on this topic over at Your Diet Sucks.

What Glycogen Depletion Actually Does to Your Running Performance

The argument for skipping fuel on runs under two hours usually goes something like this: your muscles can store about 400-500 grams of glycogen, your liver another 100 or so. That's roughly 2,000-2,400 calories of readily available carbohydrate energy. A half marathon burns maybe 1,200-1,500 calories, depending on your size and pace. So technically, you have enough stored fuel to cover the distance. Case closed, no gels needed, stop being soft.

Here's what that math ignores: glycogen depletion isn't binary. You don't run at 100% capacity until the tank hits zero and then bonk. Performance degrades progressively as glycogen decreases (Coyle, 1986). Your body starts increasing fat oxidation to compensate, which is fine for easy efforts but simply cannot supply ATP fast enough for higher intensities. The result isn't that you can't finish. It's that you slow down, your perceived effort skyrockets, and the last few miles feel like absolute death.

There's also the matter of which glycogen you're using. Your muscles preferentially burn their own local glycogen stores, and different muscles have different capacities. The glycogen in your quads isn't automatically available to your calves when they run low. And your brain runs almost exclusively on glucose. When blood sugar drops, so does your cognitive function, coordination, and mood, which is why bonking feels like an existential crisis and not just tired legs (Nybo, 2003).

"Able to Finish" vs. "Performing Your Best": Why the Distinction Matters

Here's what really gets me about the "you should be able to" framing: since when is "able to survive" the goal?

I'm able to run a marathon in cotton shorts and a trash bag. I'm able to do a long run without sleeping the night before. I'm able to race without tapering. None of these are smart, and none of them will help me perform my best.

The research on carbohydrate intake during exercise is pretty unambiguous: consuming carbs during efforts longer than about 60-90 minutes improves performance, delays fatigue, and enhances the quality of the session (Jeukendrup, 2011). This isn't about weakness. It's about optimizing the physiological conditions for your body to do what you're asking it to do.

The performance benefits of mid-run fueling are actually more pronounced at longer durations and slower paces. That coach running 1:04 is out there for just over an hour. Someone running a 2:15 half marathon is working for more than twice as long. Their glycogen demands are dramatically different, and their need for exogenous fuel is correspondingly higher. Generalizing from elite experience to recreational runners isn't just unhelpful. It's backwards.

Time, Not Distance, Determines Your Running Fueling Strategy

If there's one thing I want you to take from this post, it's this: your fueling strategy should be based on time, not distance.

A 10-mile run means something completely different for a 6:30 pace runner (about 65 minutes) versus an 11:00 pace runner (almost two hours). The distance is identical. The metabolic demands are not. The slower runner is out there longer, burning through more glycogen, accumulating more fatigue, and experiencing more blood sugar fluctuation.

Sports nutrition research suggests that for efforts lasting 1-2 hours, 30-60 grams of carbohydrate per hour can enhance performance. For efforts beyond 2-2.5 hours, that increases to 60-90 grams per hour, ideally from multiple carbohydrate sources to maximize absorption (Jeukendrup, 2014). These aren't arbitrary numbers. They're based on intestinal transport kinetics and oxidation rates.

But beyond the specific grams-per-hour recommendations, there's a more fundamental principle: fueling isn't just about preventing bonking. It's about maintaining quality. It's about finishing your long run with enough energy to actually absorb the training stimulus instead of just surviving it. It's about not feeling like garbage for the rest of the day. It's about protecting your hormonal and immune function from the stress of chronic underfueling.

Why Endurance Culture Makes Athletes Afraid to Eat

I can't talk about this without naming what's underneath: the endurance sports world has a deeply embedded belief that suffering is virtuous and that needing less, less food, less recovery, less support, makes you a better athlete.

This is, to use a technical term, utter horsesh*t.

The "I don't need gels" brag is often less about physiology and more about identity. It's a way of signaling toughness, of distinguishing yourself from the beginners with their hydration vests and their carefully portioned chews.

And it has real consequences. I hear from runners all the time who feel embarrassed to fuel during training runs because they think they haven't "earned" it yet. Who skip gels during races because they don't want to seem like they need them. Who push through bonks because asking for help feels like admitting failure.

This is how we end up with athletes, especially female athletes, especially those with histories of disordered eating, chronically underfueling in a sport that already demands enormous energy availability. The "you should be able to" messaging feeds directly into restriction, whether or not that's its intent.

How Much Should You Eat During a Run? A Non-Hardcore Guid

For runs under 60-75 minutes at easy effort: You probably don't need fuel, but there's no harm in having something small if you want it. If you're running first thing in the morning without breakfast, a gel or some sports drink can make the run feel better. Listen to your body.

For runs 75 minutes to 2 hours: Start practicing your fueling strategy. Aim for 30-60 grams of carbs per hour (with significant individual variability). This is as much about training your gut as it is about energy. You want your digestive system adapted to processing fuel while running before you ask it to do so on race day.

For runs over 2 hours: Fuel consistently. 60-90 grams of carbs per hour from multiple sources. Set a timer if you have to. Don't wait until you feel bad. By then, you're already behind.

For racing: Whatever your goal distance, fuel like your performance depends on it, because it does. Even in half marathons, even if you've gotten through training runs without eating. Racing is not the time to test your ability to suffer unnecessarily. Nothing new on race day.

And most importantly: ignore anyone who makes you feel like needing fuel is a character flaw. Your body is doing an extraordinary thing when you run. The least you can do is give it some carbohydrates.

The Bottom Line: Do You Need Gels for a Half Marathon?

For most recreational runners, yes, especially if you're running longer than 75-90 minutes. The science on carbohydrate intake during endurance exercise isn't a debate. Performance degrades with glycogen depletion, fueling during efforts over an hour improves outcomes, and the benefits are more pronounced for slower runners who are on course longer. The "I don't need gels" flex is a physiology argument dressed up as a personality trait. Don't let it talk you out of performing your best.

Got questions about fueling, training, or why endurance culture is the way it is? Join the conversation on Patreon where Kylee answers your nutrition questions every month and the community actually gets it.

References

Coyle, E. F. (1986). Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. Journal of Applied Physiology, 61(1), 165–172. https://doi.org/10.1152/jappl.1986.61.1.165

Jeukendrup, A. E. (2011). Nutrition for endurance sports: Marathon, triathlon, and road cycling. Journal of Sports Sciences, 29(sup1), S91–S99. https://doi.org/10.1080/02640414.2011.610348

Jeukendrup, A. E. (2014). A step towards personalized sports nutrition: Carbohydrate intake during exercise. Sports Medicine, 44(S1), 25–33. https://doi.org/10.1007/s40279-014-0148-z

Nybo, L. (2003). CNS fatigue and prolonged exercise: Effect of glucose supplementation. Medicine & Science in Sports & Exercise, 35(4), 589–594. https://doi.org/10.1249/01.MSS.0000058433.85789.66