The Science of Sugars in Endurance Sports
Understanding how the body breaks down carbs into sugars – and how to fuel smarter for peak performance.
Walk down the sports nutrition aisle and you’ll find gels, chews, powders, hydrogels, “superfuels,” and more. The options are overwhelming, and for many athletes, the real question is simple:
👉 Which fuel will give me energy without wrecking my gut?
To answer that, we need to zoom in on the science of sugars — and how different types of carbs are used during endurance training and racing.
Breaking Down Sugars
At the most basic level, sugar = carbohydrate. Carbs are made of carbon, hydrogen, and oxygen (CHO) in a 1:2:1 ratio. They come in two main categories:
Simple sugars (glucose, fructose, galactose, sucrose, maltose, lactose)
Complex sugars (glycogen, maltodextrin, starches, fibers)
During exercise, carbs are broken down into simple sugars and sent into the bloodstream for energy.
Glucose: the body’s primary fuel, used by almost every cell.
Fructose: processed in the liver, but when paired with glucose, it improves total carb absorption.
Galactose: converted into glucose for energy.
📌 Why this matters for endurance athletes:
In long events (Ironman, ultras, stage racing), your body can’t rely on fat alone. Carbohydrates are critical — and the type you choose affects both energy availability and gut comfort.
How Much Fuel Do You Need?
Research suggests the sweet spot for endurance performance is 90–120g CHO/hour.
But here’s the catch: the gut can only absorb so much at once. Push beyond its comfort zone and you risk GI distress (nausea, cramping, diarrhea). That’s why products like hydrogels and Cluster Dextrin have been designed — to improve absorption and reduce gut stress.
The Athlete’s Gut: Trainable & Adaptable
During long sessions, blood flow is diverted away from digestion and toward working muscles. This makes the gut more sensitive, often leading to discomfort.
Good news? The gut can be trained.
By gradually increasing carb intake during training, and experimenting with different carb sources, athletes can improve tolerance and minimize distress on race day.
Fueling Options: Sugars in Action
1. Traditional Gels
(Examples: GU, Clif, Precision Hydration)
Typically a glucose + fructose combo.
Uses multiple transportable carbs → increases absorption rate beyond glucose alone.
Effective for hitting the 90–120g/hr target with less GI upset.
2. Hydrogels
(Example: Maurten)
Standard sports drink + pectin + sodium alginate.
Forms a gel in the stomach, allowing for faster gastric emptying.
Current research: hydrogels can improve performance, reduce GI symptoms, and boost carb oxidation at high intake levels (>90g/hr).
3. Superfuels (Cluster Dextrin)
(Example: Skratch Super-High Carb Drink Mix)
Derived from corn starch; high molecular weight, low osmolality.
Faster gastric emptying = easier on the gut.
Provides a sustained release of energy thanks to its large molecular structure.
Takeaways for Coaches & Athletes
✔️ Carbs are essential for endurance performance.
✔️ The type of sugar matters — glucose alone is not enough.
✔️ Hydrogels and superfuels can reduce GI issues at higher carb intakes. My athletes test different carb combinations (glucose + fructose gels vs. hydrogels vs. Cluster Dextrin) to determine which works best for them.
✔️ The gut is trainable. Athletes must practice fueling in training, not just on race day. I encourage gradual gut training → start with 30–60g/hr and build toward 90–120g/hr.
Endurance is about more than miles and watts — it’s about fueling smart, too.
✉️ Want More Insights Like This?
My coaching focuses on practical science-based strategies to optimize your wellness and have you feeling more VIBRANT!
Reach out any time so we can chat - Lauren@ConfluenceCoach.com