Carb Loading During a Run: The Hype vs. The Reality
There’s a lot of buzz in the endurance running world right now about consuming up to 120 grams of carbohydrates per hour—especially in marathons and ultras. This strategy, often built around a glucose-fructose mix, is widely used by elite athletes chasing marginal gains.
But a question I often get asked is:
"Exactly how often should I take a jelly in a marathon?"
It’s a valid question, especially if you’re new to structured fueling.
But the reality is… you may as well be asking how to pick the winning lottery numbers.
How Long’s a Piece of String?
Why is it so hard to give a precise answer?
Because fueling isn’t just about hitting a set number of carbs per hour. It’s not that simple.
We’re all incredibly different. Some runners push themselves into the pain zone most of us can't even comprehend. Others push hard, some hold a steady pace, and some are just happy to enjoy the day and plod along.
Each of these efforts places different demands on the body—and that affects fueling.
If you're going flat out, you need to be fueling aggressively to avoid a catastrophic blow-up.
Pushing hard but not all-out? You’ll still need to fuel regularly to stay strong.
Running steady? You can afford to take in less.
Enjoying the experience at a relaxed pace? You can drip-feed your system without overthinking it.
Some runners can absorb 90–120 grams of carbs per hour. Others manage just fine with 60, 40, or even 20 grams. It all depends on your effort, metabolism, goals, and how well you’ve trained your gut.
The Science Behind High-Carb Fueling
Elite athletes have pushed the limits of carb intake using glucose and fructose blends. These two sugars are absorbed through different pathways in the gut, allowing for a higher total intake and more energy availability.
In theory, this can enhance performance—especially during races where every second counts.
But in reality, for most runners, there are a few important caveats...
Why High-Carb Strategies Aren’t for Everyone
1. Fructose Can Be a Gut Wrecker
While glucose is usually well tolerated, fructose can cause bloating, cramping, and GI issues for many. The more intense your run, the more sensitive your gut becomes.
2. Your Pre-Race Diet Matters
If you’ve already consumed fructose-heavy food or drinks before the race, adding more during the run can tip your gut over the edge.
3. Aid Station Roulette
You might train with a specific fuel, but race-day gels or drinks might have different carb types or ratios. If you’re not used to what’s on offer, it could lead to stomach issues.
4. One Size Doesn’t Fit All
Your weight, pace, sex, training level, and even temperature can influence how much carbohydrate your body needs—and can tolerate.
5. Carrying That Much Fuel is Tough
Elite runners have access to personal feed zones, custom bottles, and support teams. Most of us don’t. Trying to carry enough gels or mix to hit 90–120g/hr is awkward, bulky, and often unrealistic.
6. Overfueling is a Real Risk
More isn’t always better. Taking in too many carbs—especially during shorter or lower-intensity runs—can leave you feeling bloated, nauseous, or sluggish.
What Works for Most Runners?
The sweet spot for most people lies between 30 to 60 grams of carbohydrates per hour. That’s enough to support energy, reduce the risk of bonking, and minimize GI distress.
This can be achieved with:
1–2 energy gels per hour
A mix of sports drink and real food
Glucose or glucose–maltodextrin blends (easy on the stomach)
If you're racing all-out, train up to higher amounts. If you're aiming for a strong finish without GI issues, stick with what feels sustainable.
Can You Train Your Gut?
Yes! Gut training is a legitimate and effective strategy.
You can gradually increase the amount of carbohydrate you take in during training to build up tolerance. But always ask yourself:
Do I actually need 90–120g/hr?
Can I realistically carry and consume that much?
Will it benefit my performance, or compromise it?
Start small, be consistent, and let your goals dictate your strategy—not someone else’s fueling plan.
Elite Athletes & Mountain Fuel
It’s worth noting that elite athletes have successfully consumed Mountain Fuel Sports Jellies at up to 120g of carbs per hour over marathon distances. But they didn’t jump into that blindly.
These athletes trained their guts over long periods to tolerate that volume, fine-tuned their nutrition, and had the support to execute their plan precisely.
That’s not to say you can’t do the same—but it’s a long-term process that should be approached gradually and with care.
Final Word
Fueling is deeply personal. There’s no magic number that works for everyone. Instead of chasing arbitrary carb targets, ask:
How hard am I going to push?
What can I carry comfortably?
What fuels have I tested and trust?
What’s the right balance between performance and comfort?
Because at the end of the day…
how long is a piece of string?
Interested in trying the Mountain Fuel Sports Jelly Taster Pack?