Low Carb Training for Endurance Athletes

Traditionally, endurance athletes have consumed large amounts of carbohydrates to ensure training and racing are well-fuelled.  This makes perfect sense, given the well-documented performance benefits of carbohydrates.  Over the last decade though, research has shown the potential for even bigger training gains when carbohydrate availability is limited around training sessions (often termed ‘low carb training’).  Total Endurance Nutrition spent the last 4 weeks educating athletes from Total Tri Training on the benefits and pitfalls of low carb training, and here we share the key points from these sessions.

Let’s start with the ‘why’?

It’s worth saying from the outset here that the aim of low carb training is NOT to create an energy deficit which leads to weight loss.  What we’re actually trying to do with low carb training is teach our body to be better at burning fat.  This is incredibly important, not only because a better ability to burn fat is linked to greater performance in endurance events, like Ironman triathlon, but also to remain healthy too.

We store a large amount of fuel in our body – in the form of carbohydrate (glycogen) and fat. However the size of these stores are very different. We have a very limited amount of carbohydrate (glycogen) in our body – typically 400 kcal in the liver and 1,600 kcal in our muscle.  Now compare that to our fat stores, which have upwards of 60,000 kcal of available energy.  Clearly, if we can get more of our energy when training and racing from these fat stores, we’ll protect our limited carbohydrate stores for when we need them.   

So how does it work?

At Total Endurance Nutrition, we would always suggest that a low carb approach is best suited to easy endurance or recovery bike or run sessions.  These sessions will be at a low-to-moderate intensity, where fat is already a prominent fuel source, and the contribution from glycogen is lower.  The key principle is that by limiting carbohydrate intake before and/or during these sessions we’re teaching our body to get more of the required energy from our fat stores.  And by doing this regularly, the machinery (principally, our mitochondria) in our muscles adapts to be able to burn fat more effectively.

The easiest way to train in a low carb state is by training first thing in the morning before eating breakfast – i.e. training in a fasted state.  In this way, we’re starting the session with lower liver glycogen stores, since they become depleted overnight.  And as long as we don’t ingest any carbohydrate during the session, more of the energy we need for the session will come from our fat stores.  During these sessions we encourage athletes to simply drink a low cal electrolyte drink in order to stay hydrated.

Fuelling low carb training

Now, the term ‘fuelling’ may seem at odds with the above, but the ingestion of protein and some carbs in a specific manner can still allow the adaptation to become better at burning fat during exercise. 

Protein in particular doesn’t reduce fat burning or how our body adapts to this type of training.  And if training on an empty stomach doesn’t sound appealing, protein is a good choice to help reduce feelings of hunger. Importantly, protein can also offer some additional benefits by offsetting the breakdown of existing muscle proteins with an increased rate of building new proteins, allowing the muscle to adapt. Try consuming 20-30g of protein before or during the first 1-2 h of a low carb bike session.

If energy levels are feeling a little depleted after 1-2 h of a low carb bike ride (but you’ve still got a bit more riding to do), then taking on some carbs in the form of drinks, gels or energy bars is fine too.  This could be quite important, especially if the session is 3-5 hours long, where we still need to complete the session to get the training benefit. 20-40g of carbs per hour will provide some energy, but won’t completely blunt fat burning.  And the carbs have the added benefit of activating regions of the brain involved in reward and control of movement – so we feel better!

Reflect and recover

For those new to low carb training it is important to be honest with how you feel during and after the session.  Keep an eye on metrics; power, pace and heart rate, as well as hunger and mood.  Low mood and a higher than usual heart rate (for a given pace or power) are all signs you may need to include some protein early in the session and indicate a need to start fuelling with some carbs.

And talking of fuelling, just because this is an easy endurance session doesn’t mean we can neglect what we eat afterwards. This type of training is not aimed at creating an energy deficit, so what you eat after training is incredibly important, especially for those that have a harder session coming up later the same day or the following day.  Make sure to eat a meal soon after finishing the session that includes both carbohydrate and protein.

And a final thought – low carb training is just one part of the puzzle for an endurance athlete – but if done correctly can have a big impact on performance!

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