Let’s first address the myth that hard earned muscle will magically begin to evaporate if you don’t eat food every 2 hours. A handful of studies have shown muscle catabolism (breakdown of protein/muscle for energy) will not occur until roughly 48-72 hours into a fast. Until this time, glycogen and fat metabolism fuel the body. In fact, the opposite might be true- fasting might promote the PROTECTION and maintenance of muscle. The only possible issue would be excessive fasting (see below for how to on how to incorporate intermittent fasting into training).
Intermittent fasting can improve RECOVERY ability of athletes by reducing inflammation and optimizing immune function. Inflammation contributes to muscle soreness and fatigue following training and competition. Fasting has been shown to reduce inflammatory markers that can increase after strenuous activity, like IL-6 and TNF-alpha, and CRP which if high would impair recovery.
Also consider that energy being used for digestion is energy that could otherwise be used for recovery. Why do you think you lose your appetite when you’re sick?? It’s a survival mechanism, maintaining a fever supports the immune system recovery process when sick. But this uses a TON of energy. The body simply cannot afford to let extra energy be used for digestive processes at this time. It’s a similar idea here, by fasting you are able to divert that energy required for digestion towards repair mechanisms modulated by the immune system.
Intermittent fasting can improve athlete endurance via cellular autophagy and mitophagy. This is the removal of damaged cells and mitochondria. This is the equivalent of “cleaning house” and allows nutrients to be used for more essential processes. One of the reasons training at high altitude is so beneficial is because it increases cellular autophagy. Fasting can increase cellular autophagy by up to 500%!
The best athletes are the ones with metabolic flexibility. This is the ability to switch between burning ‘sugar’ and ‘fat’ (at the right times!). Poor metabolic flexibility means you must constantly rely on sugar for energy. This creates obvious problems, but also increases likelihood for gut issues and inflammation. Athletes who can efficiently switch back and forth are more likely to avoid “bonking” and can perform at high levels for longer.
How do I implement Intermittent Fasting into my training?
Unless your sole focus in life is muscle hypertrophy, most athletes could benefit from a minimum 12 hour overnight fast 5-7 days a week.
Intermittent fasting should not be used in competition, nor should it be used by individuals pairing high volume training with caloric restriction.
Longer fasts (14-20 hours) can be used on off days, but this should not lead to a caloric deficit unless the goal is weight loss. Low intensity workouts in a fasted state can be used regularly.
Next we will discuss the differences between males and females, and more specifics on working this into the perfect training program!
Mark P. Mattson, “Challenging Oneself Intermittently to Improve Health,” Dose-Response 12, no. 4 (October 1, 2014): dose-response.14-028.Mattson, https://doi.org/10.2203/dose-response.14-028.Mattson.
George F. Cahill, “Fuel Metabolism in Starvation,” Annual Review of Nutrition 26, no. 1 (July 18, 2006): 1–22, https://doi.org/10.1146/annurev.nutr.26.061505.111258.
Higher Activation of Autophagy in Skeletal Muscle of Mice during Endurance Exercise in the Fasted State | American Journal of Physiology-Endocrinology and Metabolism,” accessed June 7, 2018, https://www.physiology.org/doi/abs/10.1152/ajpendo.00270.2013.