I enable endurance athletes to overcome lack of energy and gut upset so that they can fuel their bodies with confidence and race to their full potential. Subscribe to my weekly 'Fuelling with Purpose' newsletter to receive endurance nutrition insights directly in your inbox.
Fuelling With Purpose — 9 December 2025
💡 Fuel For ThoughtA sweet tooth or an underfuelled day?Ever feel like you have a “sweet tooth” you just can’t tame? Or that every evening turns into a tug-of-war between you and the pantry? I hear this all the time from athletes who assume the problem is discipline… but nine times out of ten, it’s actually a fuelling gap. When you go long stretches underfuelled, whether that’s a rushed morning, a light lunch, or trying to “be good” during the day, your brain does exactly what it’s designed to do: drive you toward quick, high-energy foods at night. That isn’t a lack of willpower. It’s physiology. Blood sugar dips, hunger hormones surge, and your body sends urgent signals that it needs energy now. You’re not craving sugar because you’re addicted. And when you start fuelling consistently, everything shifts: energy rises, mood steadies, training feels smoother, and suddenly it becomes easy to be proactive rather than reactive with your nutrition. Making wiser fuelling choices becomes effortless. If evenings feel hard, don’t blame your discipline. Look upstream. A well-fuelled day creates a calm, steady evening and a stronger, more resilient athlete. 🚀 Endurance Highlights1️⃣ Inside Kilian Jornet’s WSER Nutrition: What elite adaptation looks likeOne of the biggest limitations in ultra-endurance research is that collecting meaningful data during an actual race is extremely difficult. That’s why this new case study is so extraordinary: researchers followed none other than Kilian Jornet throughout the 2025 Western States 100, measuring everything from energy expenditure to core temperature to real-time nutrition intake under genuine race pressure and up to 40°C heat. The results give us a rare glimpse into what the upper limits of human endurance actually look like. Kilian spent over 16,000 kcal during the race, averaged 86 g of carbohydrate per hour, and reached an impressive 110 g/h in the final hours without reporting any gut distress. Equally fascinating is his ability to tolerate meaningful amounts of fat early in the race. Beyond nutrition, the study also shows Kilian’s exceptional fatigue resistance. He maintained close to 85% of his critical speed for most of the race, with only a ~15% decline over 14+ hours. His core temperature peaked at 39.4°C, and despite losing over 4% of his body mass, he managed the conditions through heat acclimation, gut training, and consistent cooling strategies. These findings are a powerful reminder that gut training, strategic nutrition, and environmental preparation are essential performance tools for ultra-endurance success. 2️⃣ Should you drink to thirst or follow a set plan?Adequate hydration is crucial for ultra-endurance success, yet it’s one of the hardest things to get right. Both dehydration and overhydration can compromise performance and pose real health risks, especially in long, hot, and unpredictable events. This review compared the two main hydration strategies used by runners: programmed drinking (following a set plan based on sweat rate) and drinking to thirst (letting internal cues guide intake). Lab studies tend to favour planned hydration, showing benefits for plasma volume, core temperature, and cardiovascular stability. But in actual ultra events, where terrain, heat, gut tolerance, and aid station spacing constantly change, rigid plans often fall apart. Field research shows that many experienced runners safely and effectively drink to thirst, with no added risk of dehydration, hyponatremia, or performance decline. However, thirst alone isn’t perfect for everyone, especially athletes with high sweat rates or those racing in extreme heat. That’s why the authors recommend an approach that I also promote: use sweat testing and preparation to understand your needs, then adjust fluid intake based on thirst, environmental conditions, and gut comfort on race day. It’s the most practical and safest approach for real-world ultra-endurance demands. 🕵🏻♀️ Retail Finds*This week's product review: Precision Fuel Chew BarEnergy chews can offer a convenient alternative to energy gels or bars. Features & benefits
Things to keep in mind
Final take These chew bars can be convenient when space is limited or when you want to include other carb-dense alternatives. *Special thanks to my client Kristina from Coast To Mountain Running, who sent me a package with a wide range of products to review, including these samples. 👩🏻🍳 Kitchen CreationsI'm committing to sending the most valuable endurance nutrition newsletter. I want to make sure that every piece of content you receive includes information that is helpful to you and your journey toward achieving your personal best. Happy fuelling! Gaby | Endurance Nutrition Specialist p.s. I personally read and answer your email replies. PLUS, whenever you’re ready, here are 3 ways I can help you optimise your performance:
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Gaby Villa
I enable endurance athletes to overcome lack of energy and gut upset so that they can fuel their bodies with confidence and race to their full potential. Subscribe to my weekly 'Fuelling with Purpose' newsletter to receive endurance nutrition insights directly in your inbox.
💡 Fuel For Thought Stop panicking on race week: My chat with The Running Journey Podcast If you’ve ever felt like you “know” nutrition… until race week hits and you suddenly spiral into Google, panic-carb-loading, and second-guessing everything, this podcast episode will feel like someone turning the lights on. In Episode 153 of The Running Journey Podcast, I chat with Rob and Charlie about the real-world stuff endurance athletes actually wrestle with: the “eat clean” trap, why chasing a...
💡 Fuel For Thought Why heat changes your fuelling needs and what to do about it Training or racing in the heat places extra stress on the body. More blood is diverted to the skin to help you cool down, sweat rates increase, and your body leans more heavily on carbohydrate (glycogen) to keep you moving. Being mindful of this can make the difference between adapting well and digging a hole you don’t need. With that in mind, here are my key nutrition considerations when training or racing in the...
💡 Fuel For Thought If training is just about suffering, you're missing the point In recent weeks, I’ve come across a couple of posts that genuinely worried me. One was a CNN headline about a reporter completing a six-day hike on just 250 calories per day. Another was a runner openly endorsing underfuelling as a way to toughen up for marathon training. I get why these stories gain traction. As endurance athletes, we’re wired to respect grit. Pushing through discomfort is part of the sport’s...