Fuelling Science in Plain English

By Dr Sam Impey, Performance Nutritionist & Co-Founder of Hexis

Why We Need to Talk About Fuelling

Running is simple. Fuelling it properly hasn’t been.

“Do I really need gels in training?” “When do I take them?”

“What’s the difference between glucose and fructose?”

“Why do some gels make my stomach feel awful?”

These are the questions I’ve heard time and time again. And truthfully, most runners still rely on guesswork. They train hard, but underfuel - limiting performance, slowing recovery, and making sessions feel tougher than they need to.

That’s why, together with Puresport, I set out to simplify the science. No jargon, no complicated calculators. Just the facts that matter.

We’ve run the numbers for you.

The Basics: How Your Body Fuels a Run

When you run, your body burns two fuels - fat and carbohydrates.

At low intensity (easy runs, recovery jogs), fat and carbs do half of the work each. But as your pace or effort increases, your body switches to more carbs because they deliver energy faster.

The catch?
Your body only stores enough carbs (as glycogen) for about 90 minutes of moderate to hard running. After 60 minutes of running we start to feel fatigue from our carb (glycogen) stores beginning to run low, reducing our training quality in the last stages of our run. After that, you risk “hitting the wall”.

The solution is simple: top up your energy before you run out. That’s why we built Puresport Energy Gels to give you 30g of carbs every 30 minutes - the sweet spot for steady energy and faster recovery.

 The Science Behind It

  • Just because you take in 60g of carbs per hour doesn’t mean your body uses all 60.

    Studies show that only around 80% of what you ingest is oxidised - actually used as energy - with the rest sitting in the gut or processed later (Barber et al., 2020; Rowlands et al., 2008).

    That’s why the goal isn’t to replace everything you burn, but to fuel at a rate your body can handle efficiently.

    Most runners perform best at ~60g of carbs per hour - which equals one gel every 30 minutes.

  • Your gut has two main transporters that move carbs into your bloodstream:

    • SGLT1 for glucose-based carbs (like maltodextrin)
    • GLUT5 for fructose

    When you only take glucose, you hit a ceiling at about 60g/hour - that transporter simply can’t handle more.

    But combining glucose and fructose in a 1:0.8 ratio activates both transporters, increasing your body's ability to absorb carbs (O’Brien & Rowlands, 2011).

    That’s the foundation of Puresport’s DualCarb™ system - designed to maximise energy delivery while staying gentle on your stomach.

  • You can have perfect fuelling on paper and still ruin your run if your gut disagrees.

    Some brands use “hydrogel” additives or salts claiming they improve absorption - but the data says otherwise.
    A 2020 study found pectin-alginate gels don’t increase carb oxidation at all (Barber et al., 2020).

    Instead, we focused on a clean formula that removes unnecessary additives and supports real-world gut comfort.

    Because the best gel isn’t the one with the most carbs - it’s the one you can actually use.

  • Every runner’s physiology is different. Recent research (Podlogar et al., 2025) showed that tailoring fuelling to individual oxidation efficiency helps runners find their personal sweet spot.

    Elite athletes might push up to 90g/hour, but most runners perform optimally at 60g/hour - right where one Puresport Gel every 30 minutes lands.

    That’s science meeting simplicity.

Why You Should Fuel in Training

Most people think gels are only for race day.
They’re not.

Your gut needs training just like your legs. When you fuel properly in training, you teach your body to absorb and use carbs efficiently, which:

  • Reduces the risk of gut issues
  • Speeds up recovery

Improves long-term endurance
So if you want your body to perform on race day - train your gut too.

“You don’t save your shoes for race day. Don’t save your gels either.”

The Takeaway

Fuelling doesn’t need to be complicated.
Here’s what matters:

  • Your body burns carbs fast when running.
  • It can only absorb a limited amount per hour.
  • Combining glucose and fructose increases energy delivery.
  • Practising your fuelling in training improves absorption and recovery.

That’s why we made it simple: 30g every 30 minutes.
Backed by science, built for runners.

We’ve run the numbers for you.

PURESPORT ENERGY GELS

Puresport’s Energy Gel are designed for runners and endurance athletes who want simple, effective fuelling. Each gel delivers 30g of DualCarb™ energy in a precise 1:0.8 glucose-to-fructose ratio, supporting sustained performance and reducing gut discomfort. The natural flavours are refreshing, easy to take mid-run, and made with natural ingredients to help you fuel smarter, train stronger, and recover faster, every 30 minutes.

Launching 28.10. Sign-up now for early access.

GET EARLY ACCESS

References

  • Barber et al., Pectin-Alginate Does Not Further Enhance Exogenous Carbohydrate Oxidation in Running (2020)
  • Rowlands et al., Effect of Graded Fructose Co-ingestion with Maltodextrin on Oxidation Efficiency and Performance (2008)
  • O’Brien & Rowlands, Fructose-Maltodextrin Ratio Affects Oxidation Rate, Gut Comfort, and Performance (2011)
  • Podlogar et al., Personalised Carbohydrate Feeding During Exercise Based on Exogenous Glucose Oxidation (2025)
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