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Low Carb Training For Endurance Athletes

Low carbohydrate doesn't mean "no carbohydrates".

Today I'm going to be talking about how you can potentially manipulate your carbohydrate intake to bring about better performance gains as an endurance athlete.

The premise behind low-carbohydrate training is that it stimulates mitochondrial biogenesis, which is essentially the production of more of your muscles' fuel cells. One of the roles of mitochondria is its ability to convert oxygen to energy. Producing more energy using oxygen has two distinct advantages.

  1. You're not going to produce as much lactate at higher speeds or powers. When you start using carbohydrates as a fuel source, then you're using the glycolytic system. One of the byproducts of breaking down carbohydrates is lactate. As I've discussed before, lactate is not necessarily bad if you can clear it. However, if you're producing a lot at low intensities, this will accumulate more rapidly as intensities increase. An increase in lactate will hinder your ability to sustain these speeds or powers for any considerable amount of time, which will reduce your FTP if you're a cyclist or 10k time if you're a runner.

  1. The other added benefit is that you can use fatty acids as fuel by taking on more oxygen. Utilising more fatty acids may enable you to spare more carbohydrates and help with fat loss. Although this may not be as important for shorter events, we know that fitter athletes tend to have higher fat oxidation rates.

So just cut carbohydrates for most of your training?


The goal of training should still be to perform as best as you can. At Box Nutrition, to help with this, we follow the mantra of "fuel the work required", or matching your carbohydrate needs with the activities that you are doing.

For more demanding sessions, when you're training around your anaerobic/lactate threshold, you're going to need plenty of carbohydrates. At this point, energy will typically be coming from 100% carbohydrates, meaning that you're going to need plenty! Fuelling these sessions correctly (with carbohydrates) will enable you to perform better (exercise harder, faster, further) leading to more adaption, i.e. getting fitter.

So what about low carbohydrate training?

You probably don't have to.

However, you could experiment with some lower carbohydrate sessions.

Easy sessions don't need as much fuel. Simply reducing how much you eat these days from carbohydrates is a pragmatic way to ensure you don't' overeat. Easier workouts will also fall around your aerobic threshold or below, meaning they are unlikely to use many carbohydrates. Again, there's no need to fuel these workouts actively, and instead, the focus should be on overall intake for the day.

Training low

'Train high, sleep low' is a popular protocol where you perform a high-intensity session in the evening to deplete muscle glycogen (stored carbohydrates). Post-workout, you would refrain from eating any carbohydrates before sleeping 'low' (without replenishing glycogen stores). The next morning you would perform an additional low-intensity session after a fast to stimulate mitochondrial biogenesis.

Some issues with training low include reducing the quality of the training, an increase in perceived effort and a reduction in performance. Caffeine and a carbohydrate mouth rinse (literally swilling a carb drink around your mouth) can help fatigue and perception of effort. This type of strategy may also increase the risk of injury and illness from overreaching.

To sum up

This low carb approach is not a magic strategy and should be used with caution. There is an evident impairment of performance under low carb conditions, so these sessions should be carefully considered with the time of day, training load and intensity. Too much too soon will only hinder performance and have a detrimental effect on your training.

One must also remember that the most significant factor in improved performance is better training, not adjusting your carbohydrates. Restricting carbohydrates too much and affecting your sessions' quality will have a more substantial, negative impact on your training and performance. So fuel wisely.

If you had any questions about how to fuel your training or you're interested in metabolic testing, where we can help with your fuelling strategies, make sure you get in touch or check out the links below.


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