Having spent my time as an undergraduate studying biochemistry and human metabolism, I found the idea of fasted training an interesting topic and it remains one of my favorite training tactics nearly 4 years later. What is it and is it right for you?
Coffee, no food for breakfast
In this article, I will review basic exercise metabolism, the concept behind doing a fasted ride, how/why they work, when they do not work, and how to do your own fasted ride! Let’s get started.
During exercise, our bodies rely heavily on carbohydrates and fats to pedal our bikes. Carbohydrates can be found in relatively limited amounts as free glucose in our blood sugar or stored in larger chains within our muscle cells & liver. However, fat is stored across the body – even the thinnest of athletes have a massive amount of energy available stored throughout the body as fat.
At sufficiently low intensities (below approximately 65% of VO2peak), the body can break down the larger fat molecules and produce vast amounts of energy via aerobic respiration. However, as exercise intensity increases, the aerobic breakdown of fats is too slow to meet the energy demands. Although the body continues to utilize fats, the body becomes increasingly reliant on carbs. Carbohydrates become the body’s preferred fuel source at higher intensities since they are smaller, easier to access, and faster to break down.
Through training and nutrition, we have the capacity to manipulate the contribution of fats. This is very important since one of the key aspects of becoming a better endurance athlete is to increase our body’s ability to continue metabolizing fats at higher intensities. The thought is to burn higher quantities of fats at lower intensities and save your precious, limited carb stores for key attacks, climbs, or finishing sprints. Further, relying more heavily on fats can also help athletes avoid the dreaded bonk, which happens when our bodies run completely out of carbs.
What is fasted riding?
To put it simply, fasted training is performing exercise without eating beforehand. It means performing your morning Zwift ride without eating breakfast beforehand (which also means no cream or sugar in your morning coffee) or waiting until after your post-work turbo session to sit down for dinner.
For after the fasted ride
Does it work?
By restricting the supply of carbohydrates – either through caloric restriction or through prior exercise – it is possible to artificially limit the body’s ability to access and burn carbs. The idea behind this is to force the muscles to continue burning fats at higher intensities.
Carl Hulstron and colleagues showed that this was the case in a 2010 study. In short, cyclists completed 3 weeks of training with either high or low muscle glycogen levels. In the HIGH group, cyclists completed alternating days of aerobic rides (90 min of endurance/tempo paced riding) with HIIT sessions (8 x 5-min efforts, 1-min recovery). Conversely, the LOW group trained twice every second day, first completing 90 min of aerobic training, a 1-hour recovery and then HIIT session. They found that the power output was lower in the LOW group in the HIIT sessions – no surprise there, since they did the HIT session after 90 min of endurance riding and being low on carbs that are essential for higher power efforts. However, they also showed that fat oxidation during steady state cycling increased a whopping 31%.
Secondly, “training low” as it is often referred to, can also stimulate mitochondrial biogenesis, which simply means that your body creates more mitochondria, “the powerhouses of the cell”. A paper by Jonathan Bartlett & colleagues confirmed this by showing that key genes in the regulation of mitochondrial biogenesis were significantly higher 3-hours after performing a bout of high intensity running when the exercise was performed from a low-carb state, compared to a high-carb state.
Coffee for breakfast – No cream or sugar
How to do your own fasted ride?
As mentioned previously, most high-intensity sessions will require accessible carbs. This means that you will likely struggle to complete any all-out, full-throttle HIIT session or Zwift race. Or, even if you can complete the session, you are likely unable to achieve intensities that would maximize the benefits from those harder workouts. So, it is best to save your fasted rides for your easier endurance rides.
Most average athletes training between 5-7 hours a week can see considerable benefits to their aerobic system by adding in 1-2 sessions per week of fasted aerobic riding. It’s important not to over-do it, as you don’t want to miss out on the benefits of high-intensity sessions performed when you’re adequately fueled. Furthermore, doing too many fasted sessions can potentially down-regulate important enzymes that play a role in glucose metabolism. In other words, riding only fasted at low intensities might compromise your ability to generate short-term anaerobic power (think of your 30-sec to 6-min power range).
Remember that the primary focus of these sessions should be on low intensity, aerobic riding. When doing these sessions, try to keep the ride to no more than 2 hours before supplementing with carbs. Alternatively, you can go for a shorter ride & throw in some intervals towards the end.
I typically perform my fasted sessions first thing in the morning. I start with my morning coffee – either regular coffee black, or double-shot of espresso, along with some water. If I am heading outdoors for a fasted ride, I always pack some extra gels for myself as a “just in case”.
Get that endurance ride in
How to recover from a fasted training session
Performing the endurance training fasted is only half the equation – it’s important to focus on the recovery from these sessions as well. Eating a high-carbohydrate food immediately after the ride may decrease the benefits gained from this sort of session. Instead, try a recovery drink that delivers a small serving of carbs alongside some protein will be beneficial. Then, try to get a more substantial meal high in protein and carbs approximately 90 minutes after the training session.
Lastly, another important factor to keep in mind is that fasted sessions may increase the recovery time, compared to a similar session performed when well-fueled. The following 24 hours or so in terms of timing, this makes fasted endurance rides a solid choice before taking a day off the bike.
Bartlett, J. D., Louhelainen, J., Iqbal, Z., Cochran, A. J., Gibala, M. J., Gregson, W., … & Morton, J. P. (2013). Reduced carbohydrate availability enhances exercise-induced p53 signalling in human skeletal muscle: implications for mitochondrial biogenesis. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 304(6), R450-R458. https://pubmed.ncbi.nlm.nih.gov/20351596/
Hulston, C. J., Venables, M. C., Mann, C. H., Martin, C., Philp, A., Baar, K., & Jeukendrup, A. E. (2010). Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Medicine and Science in Sports and Exercise, 42(11), 2046-2055. https://pubmed.ncbi.nlm.nih.gov/23364526/