5 Ways Exercise Safely During Intermittent Fasting

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Medically reviewed by Kimberly Langdon, MD

Exercise Safely During Intermittent Fasting

Is exercising during intermittent fasting safe?

You can exercise safely during intermittent fasting but you would need to adjust your routine. 

Your exercises during intermittent fasting will no longer proceed like they would if you were in a well-fed state. Consider fewer high-intensity activities and more low-intensity workouts. Timing your exercise right, adopting healthy habits, and listening to your body are essential if you do not want to get hurt. 

The best time to work out while intermittent fasting

To promote the body’s natural circadian rhythm, the optimal time to exercise while intermittent fasting is usually right after waking up or shortly after. Working out (or eating) too soon to bedtime has been shown to disrupt levels of deep and REM sleep, so leave your exercise for the next day.

To ensure your safety when working out during intermittent fasting, you might need to consider the following:

  • Time your exercises properly 
  • Choose the right type of exercises 
  • Stay hydrated 
  • Fuel your workouts with the right meal 
  • Listen to your body 

Intermittent fasting is popular not only for losing weight but its health benefits.  Fasting could promote the destruction of old cells. It could also have anti-aging benefits[1] through its effects on your metabolism. 

Exercising in a fasted state might be an option for you if you want to maximize fat loss. In your fasting state, your body’s glycogen stores are depleted and your body reaches into your fat stores to fuel your exercises. 

5 Ways To Exercise Safely During Intermittent Fasting

Time Your Exercises Properly 

If you are new to intermittent fasting, combining it with exercise to burn more calories might seem like a daunting task.  

You might feel dizzy or your productivity might be far below your normal level. Time exercises when you are most productive. Timing your workouts around your eating periods might make exercising much easier.

If you are on a 5:2 intermittent fast or alternate-day fasting, you could schedule your workouts for days that you are well fed. 

That means, on the days that your daily calorie intake is about 500 to 600 calories,  you could skip exercises or perform light workouts while performing your full workouts on your complete meal days. 

If you are on the 16:8 intermittent fast, you have an eight-hour window to nourish yourself. You could time your exercise to just before breaking your fast or just before you begin your fast.  

Working out right before breaking your fast allows you to fuel your body with a nutritious meal right after burning those calories. 

The Right Types of Exercise

What are your fitness goals, to build muscle or burn fat? 

Your energy level when you are well-fed will probably be higher than while you are fasting. Therefore, your workout schedule is going to undergo some changes if you are interested in burning fat or weight training. 

Light workouts like yoga or a light cardio session can typically fit into your schedule without trouble. Even if you are hours away from breaking your fast, you could still engage in such activities.  

High-intensity interval training workouts, lifting weights, and intense aerobic exercise might not work so well for you if you are new to intermittent fasting or exercising on an empty stomach. The fast pace and high energy requirements of such exercises might take a toll on you if you have an empty stomach, affecting your productivity and increasing your chances of getting injured. 

If you want to include high-intensity exercises in your workout schedule, consider moving them to your well-fed days or right before your fasting period. 

Muscle training exercises like weight lifting will not pack as much force as they would in your well-fed state. Therefore, fasting might affect the pace at which you build muscle.

You can also consult wellness professionals on the best type of exercise for your fitness needs. 

Stay Hydrated 

Keep your water bottle filled and close to you during your workout. You will need to replace the fluids you lose by sweating as you exercise. 

Dehydration can make exercising much more difficult. It could affect your mental state causing poor motor coordination, therefore impairing your productivity and increasing your risk of injury.

Furthermore, dehydration can affect your body’s ability to regulate temperature and increase your heart rate[2].  

So, reach for your water bottle every 10-15 minutes[3] of exercise. You will also need to chug more water down at the end of your workout to help you recover properly. 

You could also use natural electrolyte drinks such as coconut water to replace lost fluids during exercise without breaking your fast. Sports drinks might not be a great alternative because of their high sugar content. 

Fuel Your workouts With the Right Meal 

You might need to provide your body with the right energy source to support your workouts.  

That is why timing your workouts to your feeding periods might be the best option for you.

You might find that working out right before you break your fast might be a great option for you. 

However, what you eat right after exercise might be almost as important as working out for achieving your goals. 

If gaining muscle mass is a high priority on your list then your body needs protein to support muscle repair. After your strength training exercises for muscle gain, you could fuel your body with a protein shake.

Your post-workout meal should contain carbs, fats, and proteins[4]. Include rich unprocessed foods in your meal so that you can gain maximum nutrition. 

Intermittent fasting does not mean that you are starving your body and you should still try to get proper nutrition during your eating window. 

Listen to Your Body 

You do not have to perform an hour workout while fasting just because other people are. 

Your body composition is different and so is your tolerance level.

Even before intermittent fasting became a trend, some people would wake up in the morning and head straight to the gym without having breakfast. If you are one of those types of people, you might find working out in a fasting state much easier. 

On the flip side, if you are used to having a pre-workout meal, then exercising while intermittent fasting can feel daunting.  

Instead of pushing yourself to hit lofty milestones and risk injury, start small. Thirty minutes or 1-hour workouts might be a great place to start for the first few weeks.  

As your body adapts and you get comfortable with working out for short durations, you could begin extending your workout times slowly. 

If you notice any discomfort while exercising, stop immediately. Your blood sugar might be low if you feel dizzy or weak. Consider fueling up with electrolyte drinks and eat a balanced meal if you get dizzy. 

Discussing with your physician will provide you with trustworthy health information.

Before you start intermittent fasting and working out, you might want to speak with your doctor. Fasted workouts could be dangerous if you have specific health conditions such as low blood pressure, eating disorders, or diabetes. 

Benefits Of Exercising During Intermittent Fasting 

Intermittent fasting has become a popular way for people to lose weight and it has brought great results for many. 

Exercising during intermittent fasting seems like another way for people to maximize the weight loss potential of this otherwise effective weight-loss diet. 

Some studies[5] observe significant weight loss in people who exercise in the fasting state over those who eat before their workout. 

However, there is no consensus on the matter because there are other studies that do not observe a significant difference[6] in the weight lost from exercising well-fed or during fasting.

The bottom line: 

Do what is best for you. If you feel like maximizing your weight potential during your fast, you could try it out with your doctor’s approval. However, you should ensure you are following the safety guidelines above. 

Cons of Exercising During Intermittent Fasting 

Exercising in a fasted state might seem like a great idea if you are only trying to lose weight but it might not be the best way to get shredded.  

To provide energy for your workouts, your body might begin breaking down muscle.  Therefore, it might be counterproductive to your goal of bodybuilding. 

Fasting might also severely affect your workout productivity. You might find that you are only able to perform a fraction of what you would normally do in the gym.

There is also the risk of dizziness, mental fog, and low blood sugar levels when you are working out while fasting. Low blood glucose and exhaustion can be dangerous if you have diabetes or low blood pressure. 

If you cannot put up with exercising while fasting, you could look for alternative ways to encourage weight loss such as supplements. You could reduce your body weight with CBD treatment.  

Studies show that CBD can encourage weight loss and you should discuss it with your doctor before you start using supplements. 

Final Thoughts 

Will exercising during intermittent fasting give you better weight loss results? 

The scientific research is conflicting. However, if you decide to workout while fasting, you should at least ensure you are doing it safely by considering the following tips:

  • Time your exercises properly 
  • Choose the right type of exercises 
  • Stay hydrated 
  • Fuel your workouts with the right meal 
  • Listen to your body 

You should consult your healthcare provider before you begin an exercise routine while fasting or starting a weight loss supplement like CBD. 


+ 6 sources

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  3. ‌Utah.edu. (2017). Tough Workouts? You Could Be Dehydrated. [online] Available at: https://healthcare.utah.edu/healthfeed/postings/2017/03/workouts-dehydration.php#:~:text=%E2%80%9CDehydration%20impairs%20your%20body%27s%20ability,also%20weakens%20your%20mental%20function. [Accessed 2 Jun. 2021].
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  6. Schoenfeld, B.J., Aragon, A.A., Wilborn, C.D., Krieger, J.W. and Sonmez, G.T. (2014). Body composition changes associated with fasted versus non-fasted aerobic exercise. Journal of the International Society of Sports Nutrition, [online] 11(1). Available at: https://jissn.biomedcentral.com/articles/10.1186/s12970-014-0054-7?source=post_page————————— [Accessed 2 Jun. 2021].

Written by:

Jennifer Anyabuine

Medically reviewed by:

Jennifer Anyabuine holds a bachelor's degree in Biochemistry from the University of Nigeria Nsukka and currently a medical student. She is a freelance medical writer specializing in creating content to improve public awareness of health topics. When she's not writing or studying, you can find her with her dogs, Chelsea and Ginger.