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Should HYROX Athletes Bet Big on Carbohydrates? Or Become 'Fat adapted'

Hyrox and carbs

Carbohydrates have long been recognised as the body's preferred energy source for high-intensity activities, offering a rapid and efficient fuel supply for muscles and brain alike. Yet, the allure of becoming "fat-adapted" suggests a different path, one where the body's vast reserves of fat become the primary energy source, promising enhanced endurance and a departure from the dreaded "bonk" associated with glycogen depletion. But does this shift toward fat adaptation hold up under the demands of HYROX competitions, or do carbohydrates retain their crown as the optimal fuel for peak athletic performance?


Fuelling the Fire: The Basics of Exercise Metabolism and Carbohydrates


Before diving into the specifics of why carbohydrates may matter for HYROX, it's essential to understand the fundamentals of exercise metabolism. At its core, metabolism during exercise involves converting the food we eat into the energy our muscles can use. This process is facilitated by two primary metabolic pathways: aerobic (with oxygen) and anaerobic (without oxygen), each playing a distinct role depending on the intensity and duration of the activity.


Aerobic vs. Anaerobic Pathways: A Balancing Act


  • Aerobic Metabolism kicks in during prolonged, less intense activities. It's highly efficient, burning carbohydrates, fats, and even protein in the presence of oxygen to produce energy. For activities like steady-state running or cycling, this pathway can sustain energy production for extended periods.

  • Anaerobic Metabolism, on the other hand, is the star during short, high-intensity bursts where immediate energy is needed. This pathway primarily uses glucose from carbohydrates to quickly generate energy without the need for oxygen. It's what powers a sprint, a heavy lift, or a rapid series of functional movements in HYROX competitions.


Why Carbohydrates Matter for HYROX Athletes

HYROX competitions demand performance within the high-intensity zones—between your first and second lactate thresholds, often reaching the 'red zone' in doubles where brief breaks allow for more intense bursts. This intensity level, combined with the nature of the exercises, specifically dictates the need for carbohydrates as the primary fuel source. Unlike fats, carbohydrates provide the rapid energy release essential for powering through sprints, jumps, and lifts, ensuring peak performance throughout.

This quick breakdown of glucose into energy is pivotal not only for physical exertion but also for cognitive functions critical to HYROX events. When you need to count your laps when knackered this becomes REALLY important (talking from from first hand experience here, yes I did 1 extra lap). So, for HYROX athletes navigating the demanding circuit of aerobic and anaerobic challenges, carbohydrates are indispensable, fuelling both the body and mind for optimal performance.

Brooks crossover for hyrox

The Brooks-Crossover concept above, illustrates how, as exercise intensity increases, our body shifts from primarily using fats to using more carbohydrates for energy. This transition occurs because carbohydrates can be broken down more quickly than fats, providing the rapid energy required for higher intensity activities. Essentially, during low-intensity exercise, the body prefers fats as a fuel source, but as you ramp up the intensity, it increasingly relies on carbohydrates to meet the immediate energy demands.


Using carbs for HYROX

Using fat as a fuel – Becoming fat adapted

 While we know carbs are key for the quick energy HYROX requires, there's a lot of talk about getting 'fat-adapted' from the endurance world. This means training your body to use fat for fuel, thinking it might help avoid running out of energy. But when we look at HYROX, with its mix of running and intense exercises, does getting fat-adapted really work? Let's dive into why this idea might not fit well with the fast-paced nature of HYROX competitions.


Why the "Fat-Adapted" Argument Can Be Flawed:


  1. Speed of Energy Conversion: Fat conversion into energy is slower than glucose conversion. For high-intensity activities requiring quick bursts of energy — like sprinting, lifting heavy weights, or the diverse challenges of a HYROX competition — relying on fat as the primary energy source will not provide the immediate energy needed for peak performance.

  2. Oxygen Efficiency: Fat requires more oxygen to convert into energy than glucose. During high-intensity exercises, where oxygen becomes a limiting factor, this can result in less efficient energy production, making it harder to sustain harder efforts. Studies show that even in low intensity activity like race walking, low carbohydrate diets impair exercise economy (use more energy).

  3. Flexibility in Energy Use: Studies show that following a prolonged low carb diet, dampens your ability to use carbs as a fuel, when they are reintroduced or when immediate energy is required. This can limit performance, especially in sports that require varying intensities, where the ability to quickly switch between energy sources is beneficial. Like in HYROX.

  4. Impact on High-Intensity Performance: Studies  have shown that while fat adaptation can benefit long-duration, lower-intensity endurance activities, it may impair performance in high-intensity intervals or activities that rely heavily on the anaerobic energy system, which primarily uses glucose for fuel. Like HYROX.

  5. Nutritional Balance and Enjoyment: Strictly adhering to a high-fat, low-carbohydrate diet to promote fat adaptation can restrict the variety of foods consumed, potentially leading to nutritional imbalances and reduced enjoyment of eating. This can impact overall health and well-being, which are crucial for optimal athletic performance.

The thunder dome hyrox


In Simple Terms:

Becoming fat-adapted is like training a race car to run on a less explosive but more abundant type of fuel. While it might work great for long, steady races (endurance events), it's not as effective when you need a sustained levels of speed or power (high-intensity activities). Plus, if you've only trained your car to run on this alternative fuel, switching back to the high-octane stuff (carbs) might not give you the immediate power boost you expect, and it could make the race less enjoyable if you're missing out on your favourite fuels.


In essence, carbohydrates are indispensable for high-intensity performance. They fuel high intensity exercise, aid recovery, and help with mental clarity during exercise. Thus, for HYROX athletes, a balanced nutritional strategy that prioritises carbohydrates for peak performance, while not neglecting the role of fats, is key to optimal performance. This approach ensures athletes are equipped with the energy and focus required to excel in the demanding environment of HYROX competitions.



Whether you’re diving into the world of HYROX competitions or striving to push your limits in high-intensity training, understanding and optimising your body's fuel sources is key to unlocking peak performance. But with all the complex and sometimes conflicting information out there, it can be challenging to know where to start.

Optimise your hyrox nutrition


That's where our HYROX-specific program comes in. Utilising advanced metabolic testing, we delve deep into your body's unique energy systems to craft a fuelling strategy that’s as unique as you are. Say goodbye to guesswork and one-size-fits-all nutrition plans. Our bespoke approach ensures that your diet is tailored to support your training, recovery, and competition goals, helping you achieve metabolic flexibility and perform at your best.


Don’t leave your performance to chance. Check out our HYROX-specific program today and see how metabolic testing can transform your approach to training and nutrition. Visit to learn more and take the first step towards your bespoke fuelling strategy.


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