108. Testing how many grams of carbs we really need per hour with Isabella Bertold

In this episode, I’m joined by Isabella Bertold, a professional cyclist and former world-class sailor, to talk about what happened when she took a test to find out exactly how much carbohydrate her body needed to fuel her cycling—and the results surprised her.

Like many endurance athletes, Isabella assumed she was fuelling well enough. But after taking a metabolic fuel test using XO Analytics, she discovered she’d been significantly underestimating her carbohydrate needs. The test revealed she could absorb between 110–128 grams of carbs per hour, far more than the 75 grams she thought was her limit.

We discuss what that means in practice—how she’s adjusted her fuelling strategy, what she’s learned from trialling different products and ratios, and why individual testing can change everything about how you train, race, and recover.

Isabella also talks about her past experience with under-fuelling, her fascination with health tech, and how she now uses tools like Hexis and skinfold tracking to monitor performance and energy balance without obsession.

We dive into the ongoing misconceptions about fuelling in women’s cycling, why proper carbohydrate intake is crucial for performance, and how a data-driven approach can replace guesswork and fear with confidence and strength on the bike.

Key themes include:

• How carbohydrate testing changes fuelling strategy

• Individual differences in carb absorption and gut tolerance

• The culture shift toward fuelling more in cycling

• The balance between data tracking and intuitive eating

• The influence of hormones and training phases on fuelling needs

• Real-world strategies for testing products and improving gut comfort

Listen on Apple Podcasts, Spotify or watch on Youtube.

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TRANSCRIPT

How Pro Cyclist Isabella Bertold Discovered She Needed More Fuel Than She Ever Imagined

As endurance athletes, many of us pride ourselves on discipline—training hard, eating clean, and pushing through fatigue. But what if that fatigue isn’t grit or lack of fitness, but a sign you’re simply not eating enough?

That’s exactly what Canadian cyclist Isabella Bertold discovered when she decided to test her carbohydrate needs.

After years of balancing elite sailing and cycling, Isabella was curious to see how well she was fuelling. Using a home-based metabolic test from XO Analytics, she aimed to get an exact number—no more guessing. What she found shocked her.

“I thought I was pretty close to where I needed to be,” Isabella says. “Maybe off by 10 grams or so. But I wasn’t even close.”

Her results showed she could handle between 110–128 grams of carbohydrate per hour, nearly double what she’d been consuming on long rides.

Why the Numbers Matter

This wasn’t just a small tweak—it reframed her entire fuelling strategy. For years, the culture in cycling (especially women’s cycling) has leaned toward “less is more” when it comes to food. But as Isabella and I discussed, this mindset can quietly limit performance, recovery, and overall health.

She’d already done plenty of experimentation—tracking how she felt at different fuelling levels, testing gels, drink mixes, and real food options. But until she had hard data, she underestimated what her body could absorb.

The Science Behind Fuelling

Carbohydrates are the body’s preferred energy source for endurance sport. Even during low-intensity “zone two” rides, cyclists can burn through hundreds of calories an hour—often 500 to 600 or more. The test revealed that Isabella’s energy demand, even at moderate intensity, required far more carbohydrate than she was providing.

When we under-fuel, our bodies start to pull from limited glycogen stores. The result? Fatigue, slower recovery, hormonal disruption, and poor adaptation to training.

Turning Data Into Action

Armed with her results, Isabella began adjusting her fuelling: spacing intake more evenly, balancing gels with drink mixes and real food, and finding products that worked for her gut. She learned that not all carbs are equal—different sugar types absorb at different rates, and flavour fatigue can make or break a race plan.

The sweet spot for her? A mix that uses a 1:0.8 ratio of glucose to fructose, allowing higher carb absorption without discomfort.

She also shifted her hydration approach, alternating between carb drinks and water, and began using one-litre bottles for longer rides to better manage intake.

Rethinking the Fear Around Fuel

Perhaps most importantly, Isabella’s story highlights the ongoing fear of “eating too much” that still lingers in sport—especially among women. The data helped her see fuelling not as indulgence, but as precision.

“This isn’t about eating for the sake of it,” she says. “It’s about giving your body what it actually needs to perform.”

It’s a message that extends beyond the bike. Whether you’re training for a race or a recreational rider, under-fuelling only holds you back. When you learn what your body truly needs—and trust that information—you unlock new levels of strength and resilience.

The Takeaway

Testing, tracking, and listening to your body don’t have to mean obsession. As Isabella puts it, data is only valuable if it leads to meaningful behaviour change.

For her, that means fuelling more strategically, using tech tools like Hexis for stage-race nutrition planning, and checking progress with simple, reliable measures like skinfold tracking instead of fixating on the scale.

Her story is a powerful reminder that optimal performance starts with adequate fuelling—and that women, in particular, benefit from challenging old myths about what “enough” really looks like.