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Can training low carb improve my running?

Feb 07, 2024

As distance runners we always aim to improve our performance. Training with low carbohydrates has gained attention as a potential strategy for runners to improve performance. While carbohydrates are a primary fuel source for endurance exercise, reducing their intake strategically may have benefits. In this blog post, we will explore training with low carbohydrates, its impact on metabolism and performance, different strategies to implement it, potential effects on body composition, associated risks, and help you decide if "training low" is a suitable option to enhance your performance.

What is training low?

Training with low carbohydrates involves strategically reducing your intake of carbohydrates during specific phases of your training. This can impact your body by:

  • Increasing your ability to burn fat as fuel for exercise: This may help spare your muscle glycogen stores. As a result, you may experience improved endurance capacity and a delayed onset of fatigue during your runs.
  • Increasing the number and function of mitochondria: Mitochondria are the energy-producing powerhouses within your muscle cells. A major goal of endurance training is to increase the number and function of mitochondria. Training with low muscle glycogen can enhance the development and function of mitochondria, which can promote increased endurance.

What are the strategies for training low?

Twice-a-day training: This strategy includes eating carbohydrates before a training session that uses up your muscle glycogen. Afterward, you restrict carbohydrates or fast during the recovery period. Later in the day, you complete a second training session with low carbohydrate availability because your muscle glycogen levels are depleted.

Sleep low: This approach involves doing a workout that depletes your glycogen stores, followed by restricting carbohydrates or fasting overnight. The challenge with this approach is that it can potentially disrupt your sleep and significantly hinder recovery. However, it has been shown to have significant effects on performance and body composition changes.

Fasted training: This method involves intentionally not eating carbohydrates before training. Many distance runners practice fasted training, which means they start their workout without eating beforehand. During the night, our liver glycogen is used to fuel important organs like the brain, so when we wake up, our liver glycogen is low. However, our muscle glycogen remains untouched, which makes it easier to do fasted training without feeling depleted.

Recover low: After a workout that depletes your glycogen stores, this approach focuses on recovering with limited carbohydrate intake or fasting. This can potentially improve your body's training adaptations following the session.

Long training session, no carbs: This strategy involves eating carbohydrates before your training session but not consuming carbohydrates during a long-duration workout. As your glycogen levels decrease, you put extra stress on your body to maintain the same intensity during the session. This added stress can potentially lead to improved training adaptations.

How does training low impact body composition?

Training with low carbohydrates can affect body composition by increasing the use of stored fat for energy. In a study with trained cyclists, researchers compared two groups: one group used the sleep low strategy during six training sessions, while the other group followed a regular routine. The group using the sleep low strategy experienced a significant decrease in fat mass, while their muscle mass and body weight remained the same. This change in body composition could potentially benefit performance by improving the ratio of power to weight, which is important for activities like running.

Does training status impact the effectiveness of train low strategies?

It is highly likely that well-trained athletes, who have already reached their peak potential through extensive endurance training, may not benefit significantly from training low strategies. Studies have shown that periodised carbohydrate restriction does not enhance their performance further. On the other hand, recreational athletes, who have more room for improvement in their physiological adaptations, may have a greater potential to benefit from training low approaches.

Are there risks associated with training low?

Training with low carbohydrates may not be suitable for everyone, particularly athletes with higher training volumes or intensities, as it can affect glycogen stores and potentially impair performance and increase the risk of injury. It's advisable to avoid low muscle glycogen training during race phases, high-intensity sessions, or periods with high training loads.

When starting a low carbohydrate training strategy, be mindful of the initial adaptation period which can lead to fatigue, reduced training quality and decreased immune function. Careful planning and monitoring are necessary to prevent negative effects on performance and health when modifying body composition through training low. Seeking guidance from an Accredited Sports Dietitian can ensure appropriate nutrient intake and optimise body composition.

What about longer-term low carb high fat diets?

Prolonged low carbohydrate intake, like in low-carb, high-fat (LCHF) diets, does not improve performance and may even hinder it. Studies show that LCHF diets impair high-intensity exercise, carbohydrate utilisation and oxygen efficiency. Consequently, they do not benefit elite endurance athletes.

On the other hand, metabolic flexibility (the ability to burn carbohydrates and fat) is essential for endurance athletes. It enables efficient use of fat stores, preservation of glycogen reserves and extended endurance capacity. While train low methods can boost fat utilisation, it's important to remember that carbohydrates are more efficient fuel, especially at higher intensities. Therefore, a balanced approach that includes both fuel sources is recommended for optimal endurance performance.


Training with low carbohydrates can be a promising approach to enhance endurance performance in distance runners. By reducing carbohydrate intake during specific training phases, athletes can improve fat utilisation, metabolic efficiency and potentially extend their endurance capacity. However, it is important to consider individual needs, training volume, and seek guidance from an Accredited Practicing Dietitian for a personalised approach and to mitigate risks. Remember, each athlete is unique and what works for one may not work for another. Stay open-minded, listen to your body's feedback, and be willing to experiment, monitor and adapt your training strategy accordingly.

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Burke et al 2017, 'Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers', The Journal of Physiology, vol. 595, iss. 9, pp. 2785-2807, doi: 10.1113/JP273230.

Burke et al 2020, 'Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible', PLOS ONE vol. 15, iss. 6: e0235592.

Geji & Nybo 2021, 'Performance effects of periodised carbohydrate restriction in endurance trained athletes - a systematic review and meta-analysis, Journal of the International Society of Sports Nutrition, vol. 18 :37.

Hawley & Burke 2010, 'Carbohydrate availability and training adaptation: Effects on cell metabolism', Exercise and Sports Sciences Reviews, vol. 38, pp. 00-00.

Impey et al 2018, 'Fuel for the work required: A theoretical framework for the carbohydrate periodisation and the glycogen threshold hypothesis, Sports Medicine,

Marquet et al 2016, 'Periodisation of carbohydrate intake: short-term effect on performance', Nutrients, vol. 8:755.

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