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Intermittent Fasting – Advantage or Detriment to Your Workouts?

Guest blog contributed by Your Fitness Dietitian intern Amanda LaPorte. You can find Amanda on Instagram at @theflexing_flexitarian

Tired of seeing fad diets everywhere? Yeah, me too. As tiring as it might be to see everything getting “keto-ified” or having a barrage of detox drinks thrown at you, there is a small part of you that is curious.
Is there really something to it? So-and-so had success doing it, maybe I could too! Curiosity is where it
starts, but it is important to take one more step before choosing to dive into a new diet: what does science

What even IS intermittent fasting?
Intermittent fasting (or IF as the kids say) has been around for thousands of years as a practice among many ancient religions. Today, athletes will adopt this lifestyle to help them lose fat but maintain muscle. The idea behind it is that when we are fasted, our main source of fuel, carbohydrates stored as glycogen in our muscles, has run out. When this happens, our body shifts to using stored fat as fuel.

There are many definitions of IF such as time-restricted feeding (TRF) or calorie restriction (CR). In time-restricted feeding, participants eat during a certain window of time each day. Common TRF eatingwindows are the 16/8 where you fast for 16 hours and eat for 8, or the 20/4 split. In complete calorie restriction, participants abstain food and liquid completely for a whole day or alternate days.

How does this impact performance?
Unfortunately, there still is not a lot of research conducted on the effect of IF on sports performance. The studies that have been done look at athletes that participate in Ramadan and either high-intensity exercise, endurance, or resistance training. In high-intensity training, there are varying results.

The majority, however, found decreased output and
time to fatigue for those in a fasted state.

 Likewise, there are not many studies on endurance sports, although there was one that looked at endurance athletes that skipped
breakfast. The results found that those that skipped did not perform as well and ate more during lunch. Lastly, we have resistance training where the results were, again, mixed. Some studies found a decrease in muscle which lead to poorer performance, another study found a decrease in fat mass, and a third found no difference at all.

What are the takeaways?
As frustrating as it may be, there is no clear answer. There simply have not been enough studies conducted to understand the long-term effects of IF on athletes, however, there is some evidence confirming that IF may lead to decrease fat mass overall. If you are considering adopting an IF lifestyle, consult with a nutrition professional to decide if it makes sense for you and your athletic goals.

Correia, J. M., Santos, I., Pezarat-Correia, P., Minderico, C., & Mendonca, G. V. (2020). Effects of Intermittent Fasting on Specific Exercise Performance Outcomes: A Systematic Review Including Meta-Analysis. Nutrients, 12(5), 1390. doi:10.3390/nu12051390
Levy, E., & Chu, T. (2019). Intermittent Fasting and Its Effects on Athletic Performance. Current Sports Medicine Reports, 18(7), 266-269. doi:10.1249/jsr.0000000000000614

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