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How to Exercise Safely and Effectively During a Fast

Abby Campbell is a Holistic Health Practitioner and President of 911 Body ResQ, an online store providing organic and non-GMO, supplements.

What Is Fasting?

Fasting is a powerful and natural way to clean out your body from excess toxins that have been accumulated from the environment and ingestion of foods. It is also the safest way to heal the body from diseases caused by inflammation, overeating, and the wrong nutrition protocol.

Relief can come in the form of periodic fasting which allows your body to rid itself of toxins. It provides cleansing, repair, and healing to your entire body including the digestive tract, liver, blood, lymphatic system, and the all the trillions of cells in your body. It even releases fatty tissues.

Many question whether it's safe to exercise during fasting periods. Science has shown that exercise is safe, but certain safety protocols must be adhered to.

Types of Fasting

There are many types of fasting, and each are conducted for a variety of reasons. There are short-term fasts as well as long-term fasts. Would you know that even the six to 10 hours of sleep you get each night is considered a fast?

Fasts may include certain food types, juice only, water only, or no foods and liquids. Therefore, you may think the type of exercise you do will depend on the type of fasting conducted. You are correct! Below are the main fasting types and how you may exercise with each according to scientific studies.

Don't push yourself while fasting. Rest and stretch during exercise if you feel the need.

Don't push yourself while fasting. Rest and stretch during exercise if you feel the need.

How Much Exercise with Short-Term Juice Fasts?

Short-term juice fasts usually last between one day to several days or a week. They may include only vegetables and fruits, juice, or water. Most are juice-only fasts. Studies were difficult to find for this particular type of fast with exercise. However, one study conducted an experiment on healthy, non-obese males.3 They were only allowed 150 to 300 calories in the form of vegetable and fruit drinks per day. There was absolutely no limitation on physical activity, and the test was for 8 days. This was compared to an earlier fast with limited physical activity in the same amount of time. The study concluded that free cholesterol levels had decreased. What can we take from this? It seems that unlimited activity on a very low calorie juice fat is safe and can even be healing to a certain extent.

How Much Exercise After an Overnight Fast?

Whether you realize it or not, you are naturally fasting each night when you sleep. The approximate number of hours one sleeps each night (or day if you work night shift) is 8 hours. However, you probably don't eat just before you go sleep, and you most likely don't eat as soon as you awaken. That adds a couple of hours onto your regular nightly (or daily) fast. All in all, you could be fasting 8 to 12 hours per day. The first meal of the day is called 'breakfast' as you are 'breaking' your fast.

There has been much controversy in the world of fitness on whether you should eat or not eat before exercising after awakening. Recent studies have shown that exercise is perfectly fine before any food is ingested and still within the fasted state. In fact, a scientific study has shown that exercise in the fasted state with cardio exercise increases fat oxidation up to 25 percent when performed for one hour.1 The study was conducted on a group of fasting cyclists and another cycling group that consumed carbohydrates during exercise. Another study reported that glucose tolerance and insulin sensitivity improved when exercising in a fasted state.2

How Much Exercise with Intermittent or Ramadan Fasting?

Intermittent fasting is a pattern of eating that alternates between periods of fasting and non-fasting. Let's go back to the 'Overnight Fast' we discussed earlier. As noted, you fast every 24 hours when you sleep for approximately 8 to 12 hours. With intermittent fasting, your fast would be a little longer within that 24 hour period. For some, it may be 16 to 20 hours while others may not eat for 20 to 24 hours. This is a long-term and ongoing fast for several weeks or months.

If you're familiar with the Muslim tradition of Ramadan, you will understand fasting a bit more. Ramadan is a time of spiritual reflection for the Muslim culture where they are to put more effort into following their Islam teachings. Ramadan is set aside for 30 days every year. The Muslim people fast during this time without food or drink (including water). It is an intermittent fast that begins at dawn and ends at sunset each day. This is approximately 14 to 16 hours of the 24 hour day in most parts of the Muslim world, and it is conducted during the waking hours. Therefore, food and drink is limited to a very few hours each day. Muslims usually eat only two meals per day during Ramadan - one just before the breaking of dawn and then another right after sunset.

Studies have been conducted on intermittent Ramadan fasting and exercise. According to one study on Ramadan fasting, high intensity exercise should be conducted after sunset.4 This was determined after the effects of fasting on performance. The exams were performed at three different times of the day (8 AM, 6 PM, and 9 PM) while performing intense exercise. It seems that the body needs time to fuel itself before a strenuous workout. However, other studies concluded without specific times of day for training safely:

Elites and professional sportsmen can continue training during Ramadan with no adverse effect on the renal function and immune and inflammatory systems. Thus, continuance of training during Ramadan can be performed safely.5

Current evidence from good, well-controlled research supports the conclusion that athletes who maintain their total energy and macronutrient intake, training load, body composition, and sleep length and quality are unlikely to suffer any substantial decrements in performance during Ramadan.6

This is good news to those who want to exercise during intermittent or Ramadan fasting. We can now conclude that unlimited exercise can be done any time of day during intermittent fasting as long as your nutrition (i.e., calories and macronutrients), as well as water intake, is in tact. However, if you are practicing Ramadan and are limiting your calorie intake with only two 'normal' meals, you may want to train after sunset.

Cardio Exercise While Fasting: Stationary Bike (34 Minutes)

WorkoutMinutesIntensity Level

Warm-up on Stationary Bike


level 4

Cycle 1


level 5

Cycle 2


level 6

Cycle 3


level 7

Cycle 4


level 8

Cycle 5


level 9

Repeat 4 Times


levels 5-9

Cycle 6


level 10



level 4



From all current studies, it is conclusive that all exercise is safe and healthy during most types of fasts. This includes long and intense cardio sessions as well as professional sports practice. Please keep in mind that long-term intermittent fasting is best done when appropriate calorie and macronutrient (i.e., protein, carbohydrates, and fats) are eaten. Appropriate water consumption is also important.

However, little studies have been conducted on long-term low-calorie fasts. If you are utilizing a vegetable and fruit juice fast for more than a week, or if you are only having water during your long-term fast, it would be wise to limit your exercise. You may want to do very light exercise if any. After all, most long-term fasts that are not intermittent fasts are usually done for spiritual or medical reasons. Resting the body during this time is probably crucial.

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No matter what type of fast you're on though, you want to make sure your water intake is high to keep yourself from dehydrating. If you are planning to do a long-term fast with limited types of food, juice, or water only, you may want to consult with your physician first.

Drink plenty of water during a fast, especially if you exercise.

Drink plenty of water during a fast, especially if you exercise.


[1] De Bock, K., Derave, W., & Eijnde, B.J., et al. (2008, January 31). Effect of Training in the Fasted State on Metabolic Responses During Exercise with Carbohydrate Intake. Journal of Applied Physiology, 104, 1045–1055. doi: 10.1152/japplphysiol.01195.2007. Retrieved from

[2] Van Proeyen, K., Szlufcik, K., & Nielens, H., et al. (2010, September 13). Training in the fasted State Improves Glucose Tolerance During Fat-Rich Diet. The Journal of Physiology, 588(21), 4289–4302. doi: 10.1113/jphysiol.2010.196493.

[3] Huber, R., Nauck, M., Ludtke, R., et al. (2003, February 10). Effects of One Week Juice Fasting on Lipid Metabolism: a Cohort Study in Healthy Subjects. Forsch Komplementarmed Klass Naturheilkd,10(1), 7-10. Retrieved from

[4] Aziz, A.R., Chia, M.Y., & Low, C.Y., et al. (2013, October). Conducting an Acute Intense Interval Exercise Session During the Ramadan Fasting Month: What is the Optimal Time of the Day? Chronobioogy International, 29(8), 1139-1150. doi: 10.3109/07420528.2012.708375. Retrieved from

[5] Khaled, T., Ahmed, C., & Zohra, G., et al. (2012, September-October). Physical activity during Ramadan fasting: Effects on body composition, hematological and biochemical parameters. IOSR Journal of Pharmacy, 2(5), 33-41. Retrieved from

[6] Chaouachi, A., Leiper, J.B., & Chtourou, H. et al. (2012). The Effects of Ramadan Intermittent Fasting on Athletic Performance: Recommendations for the Maintenance of Physical Fitness. Journal of Sports Sciences, 30(S1), S53-S73. doi: 10.1080/02640414.2012.698297. Retrieved from

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.


Sarah on October 08, 2018:

I have found this helpful


Dr Abby Campbell (author) from Charlotte, North Carolina on August 15, 2017:

Thank you for commenting, Sonia.

Sonia Sylart from UK on May 15, 2017:

This is an interesting read as I often fast by way of having a limited "window" for eating each day. Having read this, I've no excuse for putting off exercising now!

Dr Abby Campbell (author) from Charlotte, North Carolina on December 12, 2013:

Thanks for commenting, dwelburn. :-)

David from Birmingham, UK on December 08, 2013:

Great article on fasting. Yes fasted exercise is perfectly safe and has some advantages, though performance will suffer a little. And personally I don't consider a 'juice fast' to be fasting, although I know many people like to do them.

Dr Abby Campbell (author) from Charlotte, North Carolina on August 13, 2013:

Hi Ms. Dora. Thank you for taking the time to come read one of my hubs. I appreciate you. :-)

Dora Weithers from The Caribbean on August 13, 2013:

Thank you for these detailed explanations. I fast occasionally. Now that you explain the nightly fast, I can make better use of that. Very good presentation. Voted Up!

Dr Abby Campbell (author) from Charlotte, North Carolina on June 28, 2013:

Thanks for commenting, Kathryn. Yes! Now you know you can still exercise if you ever decide to do another fast. ;)

Dr Abby Campbell (author) from Charlotte, North Carolina on June 28, 2013:

Good evening, Faith. Thank you for stopping by. I too have done spiritual and medicinal fasts. Much good can come from them. :-) I hope you have a great evening.

Kathryn from Windsor, Connecticut on June 28, 2013:

This is another very interesting article to read. I fasted a few times when I was younger, and it is nice to know that exercise can still be done.

Thanks for sharing this with us!

~ Kathryn

Faith Reaper from southern USA on June 28, 2013:

Excellent article here, Abby! I have done fasts in the past for spiritual reasons.

My sister does juice fasts and she does continue with her exercise, so I am glad to read nothing negative came out of what you researched that you could find.

Thanks for the thorough and insightful information on fasting and exercise.

Voted up ++ and sharing

Blessings, Faith Reaper

Dr Abby Campbell (author) from Charlotte, North Carolina on June 28, 2013:

LOL, Bill. Do you mean we're not going to take H.O.W. on a 14 day lemonade diet? Just kidding. Thanks for stopping by and commenting anyway. I appreciate you! :-)

Bill Holland from Olympia, WA on June 28, 2013:

Abby, I'm trying to imagine me doing a fast....wait a minute....nope, it's not coming to me. :) Bev has done them, and one of her sons has too. I'll let you know if the mood ever comes over me.

Having said that, this is great information from a woman who knows her stuff for sure. Well done my friend and expert.

Have a great weekend!


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