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Understanding why carbohydrates are the preferred fuel during exercise can help athletes maintain energy, delay fatigue and improve endurance performance.
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Getting the Fuelling Right
As I write this article, I have just finished a recovery meal following my 80K (50 mile) Saturday morning training ride. This weekly ride is a sustained effort, where I aim to complete the distance in about two hours and thirty minutes. To perform at my best and maximise my enjoyment, it is crucial to carefully select my fuelling strategy.
In sports nutrition, ‘fuelling’ refers to the practical process of supplying the energy required for exercise. When done correctly, it leads to improved performance and a greater sense of well-being. For me, it's not about competing, but about being the best version of myself. Over the course of my sports nutrition career, I have also advised elite endurance athletes—including Tour de France champions, triathletes, and Olympic marathon runners—on optimal fuelling plans.
For athletes looking to support endurance sessions, the Healthspan Elite Carb Fuel product page includes serving guidance and product details.
- Fuelling is the practical process of supplying energy required for exercise.
- Getting fuelling right can improve performance and overall well-being.
- Carbohydrate strategy becomes more important as exercise duration and intensity increase.
What are Carbohydrates and Why Are They Important?
Carbohydrates are molecules composed of carbon, hydrogen, and oxygen. They are one of the three macronutrients, alongside protein and fats, and provide energy for the body. Each gram of carbohydrate supplies approximately 4 kcal of energy. Although the body can utilise fat, carbohydrates are the preferred energy source during exercise, as fat requires more oxygen to release energy compared to carbohydrates.
The harder you exercise, the more your body relies on carbohydrates for energy. However, there is a dilemma: working muscles compete with the brain for carbohydrate. The brain is a glucose-dependent tissue, requiring carbohydrate to function, and a drop in blood glucose can negatively impact both feeling and performance. The brain alone needs about 100g of carbohydrate daily.
Carbohydrates exist in various forms. The simplest type is a ‘monosaccharide’ (meaning one sugar unit), with glucose being the body’s preferred carbohydrate. Glucose is stored as glycogen, the body’s equivalent of starch. The body can also use other carbohydrates, such as fructose (found in fruit), but this must first be converted to glucose in the liver and released into the blood stream.
- Each gram of carbohydrate provides approximately 4 kcal.
- Carbohydrates are the preferred fuel source during exercise.
- The brain is glucose-dependent and needs about 100g of carbohydrate daily.
- Glucose is stored in the body as glycogen.
Carbohydrate Storage
The body has limited carbohydrate stores. Most are stored in the muscles as glycogen (between 300–700g), used by working muscles, and about 80–120g is stored in the liver. As blood glucose is depleted, the liver releases more to maintain levels. However, during intense exercise, muscle glycogen and liver stores can be used up quickly.
To put this in perspective, we store roughly 2,000–3,000 kcals as carbohydrate, whereas even a lean person can store around 100,000 kcals as fat. It is generally accepted that a well-fed individual has enough glycogen to sustain about two hours of hard exercise. Marathon runners often describe ‘hitting the wall’ after about two hours, when the body’s carbohydrate reserves are depleted, leading to a rapid decline in performance.
- Muscle glycogen stores are typically 300–700g.
- Liver glycogen stores are typically 80–120g.
- Total carbohydrate storage is roughly 2,000–3,000 kcals.
- A well-fed individual may have enough glycogen for about two hours of hard exercise.
Carbohydrate Feeding During Exercise
Having discussed the importance of carbohydrates and the impact of limited stores, it’s worth considering how carbohydrate feeding during exercise can mitigate these effects. For example, a 70kg person exercising at 70% of their maximum (moderate to high intensity, roughly marathon pace) may be getting up to 70% of their energy from carbohydrates, burning about 800 kcal per hour. This equates to approximately 560 kcal (or 140g) of carbohydrate per hour.
By consuming carbohydrate during exercise, the working muscles utilise this external source while conserving the body’s own stores.
Recent advances in exercise nutrition have improved our understanding of fuelling and led to better products. In cycling, it’s now common for riders to consume more than 100g of carbohydrate per hour. Elite marathon runners, who previously relied on water alone, now also consume more than 100g per hour during races. However, athletes must train not only their muscles but also their gut, building tolerance and absorption capacity for carbohydrates.
The body generally can absorb about 60g of glucose per hour, as glucose transporters in the gut become saturated. Fructose, however, uses a different transporter, so including fructose allows greater carbohydrate delivery. Fructose is converted to glucose in the liver and released into the blood, supplying energy to both the brain and muscles. This approach is known as the multi-fuel transport system.
The ideal ratio for rapid absorption and utilisation appears to be glucose to fructose at 1:0.8.
Healthspan Elite Carb Fuel is designed around this approach, with a carbohydrate blend of maltodextrin and fructose plus added electrolytes.
- 800 kcal per hour — Example hourly energy expenditure during sustained exercise.
- 560 kcal or 140g carbohydrate per hour — Example carbohydrate use at that intensity.
- 60g glucose per hour — Approximate absorption limit for glucose alone.
- 1:0.8 — Ideal glucose to fructose ratio for rapid absorption and utilisation.
- 100g+ per hour — Intake now commonly used by elite endurance athletes.
Choosing the Right Carbohydrate Product
To optimise fuelling, selecting the right product is essential. While glucose is commonly discussed, high-quality products often use ‘maltodextrin’, a high-tech glucose delivery system. Maltodextrins are chains of 15–20 glucose molecules that are quickly broken down in the gut, facilitating rapid glucose release. Using maltodextrins improves gastric emptying and gut tolerance compared to pure glucose.
The new Healthspan Elite Carb Fuel meets all these requirements, combining high-quality maltodextrin and fructose in the optimal 1:0.8 ratio. Each serving delivers 80g of carbohydrate and includes vital electrolytes—sodium, potassium, calcium, and magnesium—to support optimal hydration. The product comes in easy-to-use sachets, allowing for precise dosing, and mixes easily in 500ml of water. The suggested usage is one serving per hour during prolonged exercise.
Carb Fuel
80g carbohydrates per serving | Fuel for endurance
- For recovery & muscle repair
- Added electrolytes for optimal hydration
- 1:0.8 ratio of maltodextrin to fructose
- Easy-mixability
- Combines maltodextrin and fructose in the optimal 1:0.8 ratio.
- Each serving delivers 80g of carbohydrate.
- Includes sodium, potassium, calcium and magnesium.
- Mixes easily in 500ml of water.
- Suggested usage is one serving per hour during prolonged exercise.
Personal Practice
During my 80K Saturday morning ride, I use two sachets of Carb Fuel and a banana. I sip the Carb Fuel throughout the ride, which helps maintain my carbohydrate levels and hydration, allowing me to perform at my best and fully enjoy the experience.
Quality Assurance
When anyone is considering using any supplement I always suggest that they consider the quality assurance of the product. The Healthspan Elite Carb Fuel, like all of the Healthspan Elite range, are tested and registered on the Informed Sport Program.