What Happens When Runners Actually Try the Science

Most runners pick a gel and never think about it again. At the 2026 Austin Marathon, something different happened. Runners started asking why.

They did not just want a new product. They wanted to understand how fueling actually works.

What stood out was not the product. It was the questions that followed.

Here is what the science says, and what it means for your next race.

Key Takeaways

• Most runners fuel by habit, not by science. A single taste-and-learn experience can shift that.
• Isotonic delivery is not a marketing term. It solves a real problem runners feel on race day.
• Gut training is about tolerance, not absorption. It starts in training, not on race morning.
• The right carbohydrate type, amount, and timing is one of the simplest high-return changes a runner can make.

The Fuel Bar

Austin Marathon weekend. February 2026. Thousands of runners.

At the SiS Fuel Bar, the format was simple. Runners tasted gels, asked questions, and heard the science behind what they were putting in their bodies.

Most had never tried a science-backed gel formulation. Some confused isotonic gels with competitor products. The knowledge gap was real.

But the standout moment was not the tasting itself. It was the curiosity.

Runners wanted to know what made one gel different from another. They wanted to understand the “why” behind their fueling.

That curiosity, from first-time marathoners and experienced runners alike, revealed a gap between what runners use and what the science says.

The Gap Between Habit and Evidence

Most runners choose fuel the way they choose shoes. Whatever a friend recommended. Whatever was handed out at a race.

The problem is not a lack of options. It is a lack of understanding.

A 2025 study of 60 endurance athletes found that marathoners averaged just 21.7 grams of carbohydrate per hour on race day. The recommended range is 60 to 90 grams per hour. That is roughly one-third of what the evidence says they need.

Even their planned intake was only about 26 grams per hour. They were not just under-fueling. They were planning to under-fuel.

Earlier research found the same pattern. Competitive marathoners averaged 35 grams per hour, well below evidence-based targets.

The majority had not received guidance from a sports dietitian.

Education is the missing step. Not louder marketing. Not more flavors. Explaining the science in plain language changes how runners think about fueling.

What the Science Actually Says

When runners at the Fuel Bar heard the reasoning behind gel formulations, something clicked. The “why” made the “what” make sense.

Here is that science, explained the same way.

Why the Format Matters as Much as the Formula

Ask a runner what stops them from fueling enough on race day. The answer is rarely “I forgot.” It is usually the taste, the texture, or the feeling of forcing down another thick, sticky gel at mile 20.

Flavor fatigue is a real problem. When every gel tastes heavy and needs water to wash it down, runners start skipping them.

They fall short of their carbohydrate targets. Not because they lack a plan, but because the format gets in the way.

An isotonic gel has a lighter, smoother consistency than most concentrated gels. It does not require extra water to take in. That makes a practical difference when you are running hard, and your stomach is already under stress.

At the Austin Fuel Bar, this was the single most common piece of feedback.

Runners tried SiS GO Isotonic Energy Gel and noticed how easily it went down. No thick texture. No chasing it with water.

For runners used to fighting their fuel late in a race, that simplicity mattered.

Single-Source vs. Dual-Source Carbohydrate: Why the Blend Matters

Your gut handles glucose and fructose through separate channels. Most gels only use one. That means only one channel is working, even when your body could handle more.

Below 60 grams per hour, a single source is enough. Your body can process that much glucose on its own.

Above that threshold, glucose hits a ceiling. No matter how much more you take in, delivery plateaus at about 60 grams per hour.

Adding fructose opens the second channel. Total fuel delivery rises to 90 grams per hour or beyond in trained athletes.

That is a meaningful jump. For a runner hitting the wall at mile 20, the difference between 60 and 90 grams per hour changes the race. It can be the gap between holding pace and falling apart.

Intakes above 90 grams per hour require systematic gut training over weeks. They are not starting targets.

For most runners, 60 to 90 grams per hour with a dual-source blend is the target range.

In Austin, this was one of the questions runners asked most.

Half-marathon runners can often get by with a single-source gel. For the full marathon, the demand goes up, and a dual-source blend starts to matter.

SiS BETA Fuel Energy Gel delivers 40 grams of carbohydrate per serving with a 1:0.8 glucose-fructose ratio. Two per hour puts you at 80 grams. That lands in the evidence-based range.

When we walked runners through that math at the Fuel Bar, it clicked. The science gave them a reason to plan, not just grab whatever was available.

Gut Training: Start Now, Not on Race Morning

Runners who skip fueling in training and then load up on race day often pay for it. Nausea. Cramping. Worse.

Gut training means practicing your fueling strategy during training runs. Your gut gets better at tolerating fuel at a pace.

This is about tolerance, not absorption.

Start with moderate-effort long runs. Build up gradually.

Research supports a minimum of two weeks of repeated exposure to improve tolerance. Begin at least four to six weeks before a goal race.

Aim for two or more practice sessions per week, increasing intake each time.

Race day should never be the first time you fuel at your target rate.

What to Do Differently in Your Next Training Block

• Know your carb target. For races over 2.5 hours, aim for 60 to 90 grams of carbohydrate per hour. That is the evidence-based range for most runners.
• Match the product to the target. Below 60 grams per hour, a single-source gel works. Above 60 grams per hour, switch to a glucose-fructose blend.
• Start gut training now. Practice your race-day fueling plan during long runs. Begin at least four to six weeks before your goal race.
• Read the label. If a gel needs water to work, that changes your hydration plan. If it does not, that simplifies logistics.
• Do not wing it on race morning. The most curious runners at Austin were also the ones most likely to guess on race day. A plan beats improvisation every time.

The Bottom Line

The runners in Austin did not need to be convinced that fueling matters. They needed someone to explain how it works in plain language.

That is the real gap. Not products, but understanding.

A fueling plan built on the right carbohydrate, the right amount, and enough practice is one of the simplest upgrades available.

It does not require talent or extra training. Just a plan and the willingness to practice it.

Under-fueling is not just a race-day problem. Runners who consistently eat below their training demand pay for it with flat workouts, slow recovery, and stalled progress.

The science is available. The products exist. The only missing piece is understanding what your body needs and building a plan around it.

References

Burke, L.M., Jeukendrup, A.E., Jones, A.M., and Mooses, M. (2019). Contemporary Nutrition Strategies to Optimize Performance in Distance Runners and Race Walkers. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 117-129.
Cox, G.R., Clark, S.A., Cox, A.J., et al. (2010). Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. Journal of Applied Physiology, 109(1), 126-134.
Jentjens, R.L., Moseley, L., Waring, R.H., et al. (2004). Oxidation of combined ingestion of glucose and fructose during exercise. Journal of Applied Physiology, 96(4), 1277-1284.
Jeukendrup, A.E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20(7-8), 669-677.
Jeukendrup, A.E. (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition and Metabolic Care, 13(4), 452-457.
Jeukendrup, A.E. (2017). Training the gut for athletes. Sports Medicine, 47(Suppl 1), 101-110.
Jeukendrup, A.E. and Jentjens, R. (2000). Oxidation of carbohydrate feedings during prolonged exercise. Sports Medicine, 29(6), 407-424.
Lanpir, E., Eroglu, I., Ozyildirim, C., and Louis, J. (2025). Under Consumed and Overestimated: Discrepancies in Race-Day Carbohydrate Intake Among Endurance Athletes. European Journal of Sport Science.
Pfeiffer, B., Stellingwerff, T., Hodgson, A.B., et al. (2012). Nutritional intake and gastrointestinal problems during competitive endurance events. Medicine & Science in Sports & Exercise, 44(2), 344-351.
Stellingwerff, T. and Cox, G.R. (2014). Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Applied Physiology, Nutrition, and Metabolism, 39(9), 998-1011.