Fasted Endurance Exercise: The what, who and how!

Fasted exercise, is a hot topic in exercise and nutrition circles, however, not much is known about when, how or who should be undertaking this nutritional intervention. So we will be addressing three main questions, what is it, who would benefit most and how can I do this?

The Science!

So when you think of protein, the first thing that probably springs to mind is chicken or steak. However, from a molecular point of view we need to adjust our view into what they actually represent. Within each of your cells there are thousands of proteins, each performing a very important function. So rather than looking at them as large structures like chicken or beef, we need to see them as very small cogs, all joining together to provide function and that overall large structure. If one of these cogs is not functioning correctly or at all then this makes us more succeptible to disease and illness.

Some of these key functions include transport, enzymatic roles, movement, signalling, structure and regulation. All of which are very important but for the purposes of this article we will look more specifically at the role of proteins in signalling and regulation. When we exercise we express different proteins, with endurance exercise increasing mitochondrial proteins and resistance exercise seeing a development in myofibrillar proteins. As a result of these different expressions, we see different phenotypes occur. Endurance athletes typically will be lean and light with higher fatigue resistance, whereas strength athletes will see higher body masses and skeletal muscle.

So why is all of this relevant, well if you can modify your training and nutrition to express greater percentages of these proteins, then this should, in theory, translate to an increased likelihood of performance improvements. For example, one of the major determining factors to endurance performance is your lactate threshold, which is how intensely you can exercise before the amount of lactate produced and the associated acidosis, overwhelms the clearance capacity, thereby giving sensations of fatigue and impairing performance. Now, lactate threshold is determined by a number of factors, including aerobic enzyme activity (mitochondrial density and mass), number of slow twitch fibres and capillary density. All three of these factors are under the control of a single protein.

This protein is known as PGC-1α, nicked named the master regulator. When switched on or activated, PGC-1α converges onto other proteins further down the chain, of which these other proteins (transcription factors) do not 'work' unless PGC-1α is present. Once these steps have been initiated the transcription factors can read the DNA present in the nucleus and mitochondria, thereby producing more of the proteins that produce more blood vessels, mitochondria and other key endurance adaptations. This whole process is driven by exercise, when we contract our muscles we change the energy status of the cell, produce reactive oxygen species alonside other metabolites or stressors and it is these responses to exercise that drive this PGC-1α pathway.

Even with normal endurance training, increases in PGC-1α activity is present. However, the major question is can we optimise this process and what might the benefits be? So the short answer is yes we can improve PGC-1α expression, and if we can do this then theorectically we can increase mitochondrial content in the muscle, increase the number of blood vessels alongside other adaptations, therefore you should see increases in economy, speed/power, maximal oxygen consumption and lactate threshold.

Right, how to do this?

Train

So the first strategy is to train regularly, as evidence produce by Bartlett and colleagues established that PGC-1α mRNA which we can treat as an intermediary to the full PGC-1α protein is increased 3 hours after exercise. However, the data showed no improvement in PGC-1α proteins up to 24 hours after the exercise bout. Therefore, continually exercising is needed in order to produce more of the PGC-1α proteins. However, the good news is it doesn't take too long. Data presented by Perry et al. showed after only 3 consecutive days of training significant increases in PGC-1α content were observed.

Nutrition

Evidence has indicated that manipulating substrates can change the expression of these protein pathways. In 2013, Psilander showed that if you train in a low glycogen state you can improve PGC-1α mRNA content. Therefore, as indicated above, undertaking train-low sessions frequently may see improvements in the PGC-1α protein content. One possible mechanism behind this is the additional energy stress placed on the cells results in a heightened response of AMPK which is sensitive to energy availability and interacts with PGC-1α when activated.

Combining these two

So we previously identified both the role of exercise and nutrition on PGC-1α, but it is really about combining these two together to get the best result. So the aim of your session should be to undertake exercise in a glycogen depleted state, this should in theory then switch on these pathways.

Some ways in which you can achieve this are as follows:

1. Train first thing in the morning before breakfast, consuming only water during the session or if it is a particularly hard session, utilise caffeine supplements or carbohydrate mouth rinsing (more on that another time).
2. Undertake an intense session in the evening and either consume no food before sleep or a protein only meal.
3. Perform two sessions in the day and limit carbohydrate intake after the first bout.

With all of the above strategies it is important to keep protein intake high (1.6 - 1.8 g/kg BW/day) during this time so that muscle tissue is more likely to be protected and the evidence suggests consuming protein meals does not inhibit the mechanisms outlined above. So if you can't exercise on an empty stomach then you could have a high protein breakfast to fill you up before you go out and know that it will not be detrimental to the session aims.

Is this right for me?

So you hopefully understand why you might conduct these types of sessions and ways in which you can go about it. But it is important to note when it is appropriate to use fasted or carbohydrate restricted training and when it may be more prudent to consume carbohydrate.

If you undertake exercise or compete in competitions that are prolonged then the adaptive benefits we see with this type of strategy may be important to you, particularly as improvements in fat metabolism are seen. However, it is important to note that these improvements in fat metabolism do not necessarily translate to improved performance and this is partly due to the requirements to have access to endogenous and exogenous carbohydrates when competing as the need to produce power quickly in situations such as hill climbs and this explosive power development is not often seen to funded by fat metabolism. So the key point here is to have a mixture of high carbohydrate sessions and low muscle glycogen sessions.

It is also important to identify the potential declines in intensity seen when performing a train low strategy. So it may not be appropriate to undertake these types of sessions whereby high intensity is required from the session in order to meet its aims. However, these can be combined at times but again there is a caveat for its use and that is potential effects on immune function. Chronic train low sessions can potentially lead to more pronounced susceptibility to illness or injury. Therefore, these type of sessions should be restricted.

So if you are planning on performing these types of sessions then the following guidelines should be considered:

1. Perform 1 to 2 train low sessions per week.
2. Utilise carbohydrate mouth rinsing and/or caffeine to maintain intensity.
3. Restrict train low sessions when close to comptetition date and focus more on carbohydrate utilisation strategies.
4. Consume a high protein diet during blocks of train low sessions to protect muscle tissue.