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Run and fasting : can I run while intermittent fasting ?

If you're fond of running and want to do intermittent fasting, you may have questions. Here are the answers.
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Summary

Intermittent fasting is the practice of limiting the time during which food is consumed. While it does not necessarily involve a reduction or limitation of energy intake (in the form of calories), some people use it as a strategy for weight loss as well as to detox and cleanse.

Because of this potential to reduce the daily energy intake, the practice of intermittent fasting is approached with care by runners as it is sometimes feared that fasting could hinder running performance. On the contrary, there are also some who champion the practice of intermittent fasting as a way to improve running. Below are some pros and cons to consider before opting to try or avoid intermittent fasting as a runner. 

Written by
Dr. Sara Diana Garduno Diaz
PhD & Senior Nutrition Consultant


Best practices when running and fasting


Running is very energy-demanding, which is why it is important to make sure to eat normally within the non-fasting hours. That means consuming sufficient energy and nutrients to cover running demands as well as daily needs and fuel and nutrients to repair any damage that may occur on the body from training. 


In addition to securing an adequate energy supply for the running sessions, it is important to remember two more points: hydration and recovery. Depending on the type of fasting program being followed, fluids may or may not be consumed. If water fasting is being practiced this may not be a major concern. However, it is important to ensure sufficient hydration considering the extra demands for salts and fluids when running. 


Recovery from a run must also be considered. This means paying attention to the running schedule and planning fasting periods not just around those training sessions, but also around the recovery periods. During recovery the body needs to replenish energy stores in the muscles and liver, in order to do that it must have a supply of sugars, amino acids and other nutrients to draw from. 


Potential benefits of running while fasting

Benefits of running while fasting.

The reason why many are interested in running while fasting is the promise of burning more fat as fuel, leading to weight loss, a leaner physique and possibly enhanced performance.

Normally, the body uses sugars (glycogen) for fuel over time. However, because the body’s glycogen stores (in the muscles and liver) are limited, fasted running forces the body to turn to fat. Overtime, with adaptation, the body will learn how to burn fat, versus glycogen, providing sustainability during longer aerobic runs. This is the reason why more and more runners are looking into intermittent fasting as part of their training regime.


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Before running on an empty tank

A strategy that is often followed with great results by runners wishing to fast is to preload before a running session. This means eating sufficiently to have full energy storages in the liver and muscles before running in a fasting state.

This can be achieved with some planning and by finding a fasting schedule that works in combination with the running schedule as discussed above. 


Try different fasting plans

Woman running in the rain.

The duration and frequency with which a runner fasts will have different effects on their performance. In addition to 16:8 there are strategies like 5:2, which involve eating normally for five days of the week and practicing significant calorie restriction or fasting on the other two (non-consecutive) days of the week.

Some people do better with a 1:1 approach instead, with calorie restriction or fasting every other day, or at the other end of the spectrum, with fasting one day a week.


Things to look out for

When giving running while fasting a go, it is important that you pay attention to how fasting affects your energy levels and running performance. Other areas of life that may be affected include the quality of sleep, mood, digestive health, work focus, and overall feelings of wellbeing. 


Give it a try

If you are a runner and considering intermittent fasting, the best thing to do is to experiment with various forms of fasting and find the practice that works best for you.


References:

  1. Correia, Joana M., et al. "Effects of intermittent fasting on specific exercise performance outcomes: A systematic review including meta-analysis." Nutrients 12.5 (2020).
  2. Levy, Emily, and Thomas Chu. "Intermittent fasting and its effects on athletic performance: a review." Current sports medicine reports 18.7 (2019): 266-269.
  3. Brisswalter, Jeanick, et al. "Effects of Ramadan intermittent fasting on middle-distance running performance in well-trained runners." Clinical Journal of Sport Medicine 21.5 (2011): 422-427.
  4. Chaouachi, Anis, et al. "The effects of Ramadan intermittent fasting on athletic performance: recommendations for the maintenance of physical fitness." Journal of sports sciences30.sup1 (2012): S53-S73.
  5. Scott, Jonathan PR, et al. "Effect of fasting versus feeding on the bone metabolic response to running." Bone 51.6 (2012): 990-999.


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