It’s no secret that triathlon is a physically demanding sport with high energy demands, for which the body relies primarily on carbohydrates to fuel the body. The body stores carbohydrates in the form of glycogen, which is then utilised as a fuel source during both high-intensity exercise and prolonged aerobic exercise. However, the limitation with utilising glycogen as a fuel source, is that the body can only store a certain amount.

Once glycogen stores run out, the body must rely on fat as a fuel source, which takes much longer to be broken down and used as energy. This switch to slower fuel utilisation is commonly associated with the “hitting the wall” experience. You’ll experience a slowing of pace and increase in pain and fatigue, which makes it incredibly difficult to maintain your prior intensity.

The common strategy to respond to this is ensuring the body is adequately fuelled and re-fuelled with carbohydrates during prolonged, intense exercise. However, emerging research has also been focused on methods which allow the body to burn fuel more efficiently. For example, strategies which may allow the body to spare carbohydrate stores and more readily access fat stores for fuel during exercise. Early studies in this area saw training in a carbohydrate depleted state was sustained for longer periods than training in a high carbohydrate state. This strategy seemed to produce a greater ability to burn fat as fuel during exercise.


What is fasted training and how does it work for triathletes?

Fasted training, or “training low” is one method used to enhance the adaptations in the body which occur as a result of exercise and training, to enhance fat utilisation and improve performance.

During exercise, the body is placed under stress, which signals processes and pathways for training adaptation to occur. Fasted training works by signalling specific processes in the body which may help to enhance fat utilisation. There are various methods of fasted training including a low carbohydrate diet, training after an overnight fast, no carbohydrates during recovery, long training sessions without carbohydrate intake, training twice a day or low carbohydrate intake before sleeping.

So, what are the proposed benefits of triathlon training in a fasted state?

The proposed benefit of fasted training is the enhancement of training adaptations and therefore enhancement of the body’s ability to burn fat as fuel. Research has suggested interesting physiological outcomes and mechanism for this. These include;

  • An increase in the transcription (production) of various genes involved in training adaptation and metabolism.
  • An increased activity of important signalling molecules. More specifically, the molecules involved in the production of mitochondria. Mitochondria are organelles (which are like small organs within a cell) where the burning of fuel takes place in our bodies.


Are there any downsides to training while fasting?

There are, however, some important considerations when deciding whether this will be a useful strategy for your training.

Firstly, it’s important to understand the risks of under fuelling which may result from poorly planned carbohydrate restriction. Carbohydrates are an essential fuel for high-intensity exercise and so restricting carbohydrates may not only limit the potential intensity of your training but can also lead to a negative energy balance. Depleting the body of carbohydrate at times when it is a particularly important fuel source can lead to health impacts such as the increased risk of injury and suppressed immunity. Because of this, it’s essential that this strategy be used within intentional periodisation of nutrition, where carbohydrates may be withheld at appropriate times to enhance training adaptation. This should be done so under the guidance of an Accredited Practising Dietitian to ensure your health and safety.

Secondly, when considering the appropriateness of a nutrition strategy, it’s helpful to consider available research. At this point, whilst there have been encouraging findings, more research in this area is needed to be confident of its impact on exercise and performance. Despite benefits to training adaptation which have been seen, research is yet to see this transferred to significant improvements in performance.


Key takeaways

Given the demanding nature of triathlon, there is a benefit to strategies which may enhance the body’s fuel-burning efficiency. Fasted training presents one potential strategy to do so. However, with more research needed and the potential risks associated with poor use of this strategy, it is essential that it is used under the guidance of an experienced Sports Dietitian to ensure your health, safety and most effective use.