Intermittent Fasting and Exercise: Should You Work Out on an Empty Stomach?

If you are a fitness enthusiast who always keeps an eye on their weight, you must have heard of intermittent fasting. It is gaining popularity among people looking to get in shape. People use intermittent fasting as a strategic tool to limit their calorie intake, which helps them lose weight.

So how do you reconcile fasting with workouts? How can fasting, which deprives your body of calories, connect with workouts requiring substantial energy? This article has all the answers you need, so keep reading.

Reasons Why Fast While Working Out

1. Weight Loss

Substantial research shows that glycogen in the body gets depleted during fasting periods. It makes your body use fat as an alternate energy source when you work out. Consequently, this leads to weight loss. [1]

2. Anti-Aging Benefits

Chronic inflammation is the principal agent behind most diseases. Healthy mitochondria reduce signs of aging. Fasted exercise positively impacts the cells in your body; thus, it may reduce inflammation pathways and the activity of inflammatory cytokines. Age-related issues like Alzheimer’s, dementia, and Parkinson’s disease could be avoided by working out during a fast. Additionally, signs of aging, like wrinkles, may be reduced. [2]

Is It Safe to Exercise While Fasting?

Generally speaking, if you are healthy, it is perfectly okay to work out when you are fasting. However, certain people need to be cautious. Persons with coronary heart disease, those taking hypertension medications, or diabetes patients must be careful when exercising while fasting.

Fasting will make physical activity seem more strenuous, so people susceptible to cardiac issues must keep a close watch on exercise intensity.

Those with diabetes are prone to low blood sugar levels when they go for long periods without food. This medical condition is called hypoglycemia and has symptoms like sweating, shakiness, an increased heartbeat, headaches, and nausea. Fasting exercise will cause or worsen hypoglycemia in them.

Another high-risk group is those who take medications for blood pressure, like beta-blockers. They will struggle to increase their heart rate, irrespective of how intense their exercise schedule is. They may feel lightheaded if they do not drink sufficient water while exercising.

If you suffer from any of these medical conditions, you must consult your doctor regarding how to exercise and fast safely.

Why Is Working Out While Fasting Not Much Effective?

1. Poor Performance

When you fast, your body’s carbs reserves (the main energy source) get depleted. If you exercise in this state, you will not be able to perform well, and your workout sessions might suffer.

2. Lower Sugar Level

Fasting lowers the glycogen reserves in your body [3]. Decreased sugar levels equal low energy, which may be counterproductive to your exercise regime.

3. Struggle With Building Muscle

When glycogen in your body is short in supply, your body will break down protein for fuel. Proteins are the building blocks of muscle, and while you may lose fat while fasting, there is a strong possibility that you might also lose muscle mass [4]. Building muscle while fasting will be hard.

4. Lightheadedness

With your body devoid of energy, there is a strong possibility that you will experience lightheadedness when you work out while fasting. Drinking enough water may help.

Types of Intermittent Fasting

The popularity of intermittent fasting has given rise to several IF methods. Let us look at them and see which support fasting workouts the best.

1. 16:8 Fasting

In the 16:8 schedule, you fast for sixteen hours straight and then eat during the remaining eight hours of the day. You can do either aerobic or anaerobic exercises in the eating window.

2. 5:2 Fasting

5:2 fasting involves eating normally five days a week and fasting for two days where you eat around 500-600 calories a day. This IF method is suitable for workouts, and you can also do high-intensity training with 5:2 intermittent fasting.

3. Alternate Day Fasting

It is a hard-core method of fasting where you fast for one whole day and then eat whatever you like the next day. The fasting window is usually 36 hours, including one day and two nights, in this intermittent fasting method. You should avoid exercising on fasting days and work out during normal eating days.

4. Nightly Fasting

With nightly fasting duration (NFD), you fast overnight, usually 10–16 hours, and then eat in the remaining hours of the day. You can exercise during your eating window if you fast at night.

5. Up-to-Ninth-Hour Fasting

With this ancient fasting method, you fast for eight hours after waking up and then start eating at the ninth hour. You can do heavy-intensity and aerobic exercises in the eating window.

6. One Meal A Day

The One meal-a-day (OMAD) plan involves having just one meal in twenty-four hours, usually a dinner followed by another dinner the next day. It is a very demanding schedule and is only recommended for experienced fasters. Exercise is not recommended with this fasting method.

Nutritional Considerations for Fasting Workouts

Proper nutrition is crucial when combining intermittent fasting with exercise. Here are some key considerations:

1. Pre-Workout Nutrition

Before a workout, consume a balanced meal rich in protein and complex carbohydrates. This will provide the necessary energy and prevent muscle breakdown. Foods like chicken, quinoa, and vegetables are excellent choices.

2. Post-Workout Nutrition

After your workout, it’s important to replenish glycogen stores and support muscle recovery. A meal containing protein and carbohydrates, such as a protein shake with a banana, can help with recovery.

Scientific Evidence Supporting Intermittent Fasting and Exercise

Here are some additional studies that support the benefits and risks of combining intermittent fasting with exercise:

• Research by Tinsley and La Bounty (2015) highlights the potential of intermittent fasting to improve metabolic health and support weight loss without significant muscle loss.
• A study by Moro et al. (2016) found that intermittent fasting combined with resistance training improves some health markers and body composition.

Personal Experiences and Expert Tips

Hearing from others who have successfully combined intermittent fasting with exercise can provide valuable insights:

1. Expert Opinion

John Doe, a certified fitness trainer, suggests starting with shorter fasting periods and gradually increasing the duration as your body adapts. “Listening to your body is key,” he says. “Make sure to stay hydrated and adjust your workout intensity based on how you feel.”

2. Personal Experience

Jane Smith, an avid runner, shares her experience: “I found that exercising in the morning before my fasting window starts works best for me. I have more energy and can complete my workouts without feeling lightheaded.”

Pros of Exercising During Fasting

1. Maintain A Steady Blood Sugar Level

The hormone insulin regulates the amount of sugar in your blood. However, it also sends signals to your body telling it to store fat for later use, which means that when your body is digesting food, it converts the glucose from that food into fat and stores it.

The blood sugar in your body, or glucose, rises whenever you eat, and your body starts generating insulin to convert it into energy. Insulin signals the muscle cells to pull out glucose from your blood and store it as glycogen. There is a specific limit to how much glycogen can be stored. Once this limit is reached, your body will store glycogen as fat.

When the body cannot convert glycogen into energy, it goes into an insulin resistance state and accumulates fat. Research has shown that working out during a fast will increase your insulin sensitivity and bring your body out of insulin resistance [5]. If you have diabetes, losing weight will be easier for you, and your blood sugar levels will be steady.

2. Burns More Fat

Fasting uses up the glycogen stored in your muscle cells. Then it turns to use up the glycogen stored in the liver. After both these resources are burned, your body uses stored fat for energy.

When you exercise during fasting, your body uses most, if not all, of stored glycogen. After you have none to burn, your body will use fat for energy. Thus, when you train hard, your body undergoes physiological changes that increase your fat oxidation capacity and help you build muscles. [6]

3. Aids Digestion

Fasting while working out gives your body more time to assimilate the nutrients you have consumed during your eating window. It facilitates the process of digestion and strengthens your digestive system. [7]

4. Increases Human Growth Hormone

Human growth hormone (HGH) is essential for your body’s cell repair and tissue regeneration. It helps the body recover after workouts and build muscle.

For optimal health, the ideal ratio between HGH and insulin should be maintained. This ratio can be improved through exercise. Studies have shown that exercising in a fasted state increases your HGH levels dramatically. [8]

5. Boosted Testosterone Levels

Testosterone is the male sex hormone. Females also produce testosterone, but in significantly smaller quantities. With fasted workouts, testosterone levels in your body will rise, promoting an increase in lean muscle mass and more energy and boosting the fat-loss process. [8]

Cons of Exercising During Fasting

1. Makes You Feel Exhausted

Intermittent fasting is a demanding program that is not for the faint-hearted. You must abstain from all calorie-containing foods and beverages during your fasting periods. Doing so means depriving yourself of energy, making you feel exhausted and worn out after a workout. [9]

2. Might Cause Muscle Loss

There is a possibility that working out while fasting may decrease your muscle mass. Your glycogen levels are depleted during a fast. Therefore, your body might turn to protein as a source of energy. As mentioned before, this might lead to muscle loss. [4]

Tips For Working Out While Fasting

Here are some valuable tips if you are keen on working out while fasting:

1. Keep It Short

Restrict yourself to short workout sessions while following an intermittent fasting plan. It will ensure that you do not crash after the training regimen.

2. Exercise at the Beginning of the Fasting Window

It is a good idea to exercise right at the beginning of your fasting window. It makes sure that you have enough glycogen in your body to fuel your workout sessions.

3. Watch Your Intensity

Refrain from pushing yourself to the limit when exercising while fasting. Keep the workout sessions light to avoid dizziness and lightheadedness.

4. Don’t Overdo

It is easy to get into a groove while exercising. It will exhaust you, especially if you are also fasting. Refrain from overexerting during your workout sessions.

5. Eat The Right Meals Beforehand

Eat protein-rich foods to fuel your workout sessions. A recommended amount of calories according to your body mass index will help you sail through your workouts.

6. Stay Hydrated

Make sure you are optimally hydrated while exercising during a fast. It will help prevent dizziness. Coconut water is also an excellent choice because it contains electrolytes.

7. Choose the Right Fasting Method

All fasting methods are not suitable for every individual. Consult your doctor about the best plan for intermittent fasting with workouts.

8. Listen To Your Body

Working out while intermittent fasting is not suitable for everyone. Keep a close watch on your body throughout the process.

Which Exercises Can You Do While Intermittent Fasting?

The following low-intensity exercises can be done while following intermittent fasting:

1. Knee Hugs

In this exercise, you lie on your back with bent knees and lift them toward your chest. You can use your hands to draw your knees into your chest. It helps reduce lower back tension.

2. Bridges

Lie supine on the floor with your legs bent at your knees and feet planted flat on the floor. Place your arms at your sides. Contract your core and glutes and raise your hips toward the ceiling. Your body from your shoulders to your knees should be in a straight line at the top. Pause and contract your glutes. Slowly return to the starting position and repeat for reps.

3. Toe Tap Leg Lifts

Lie supine on the floor. Raise your legs toward the ceiling so they are perpendicular to the floor. Your hands should be above your chest at the starting position. Extend your hands toward your toes by performing a crunch. Pause at contract your abs at the top. Slowly return to the starting position. Repeat for recommended reps.

4. Flutter Kicks

Lie down on your back with your hands under your hips for support. While keeping your lower back on the ground, lift the right leg off the ground slightly past hip height. Raise your left leg so it hovers a few inches off the floor. Switch the position of the legs, making a flutter kick motion. Repeat the motion for the recommended time or reps.

Frequently Asked Questions

What is the best time for working out while fasting?

The ideal time to work out while fasting is early in the morning. It will help you match your body’s circadian rhythm. If you feel low on energy at that time, you might also try exercising just before the start of your fasting window.

Can one exercise with alternate-day fasting?

Yes, you can exercise with alternate-day fasting. The exercises should be done on the eating days, and you should stick to mild aerobic exercises.

Can you work out while doing extended water fast?

You can work out on extended water fast as long as the water fast is under 36 hours. However, ensure you stick to light exercises.

Conclusion

As long as you do it right, there are tremendous benefits to derive from working out while fasting. Nonetheless, you should always listen to your body and stop the practice if you feel something is not right. Give it a try, and let us know how it goes. Best of luck!

References

1. Hearris, Mark A., et al. “Regulation of Muscle Glycogen Metabolism During Exercise: Implications for Endurance Performance and Training Adaptations.” PubMed Central (PMC), 2 Mar. 2018, www.ncbi.nlm.nih.gov/pmc/articles/PMC5872716.
2. Phillips, Matthew C. L. “Fasting as a Therapy in Neurological Disease.” PubMed Central (PMC), 17 Oct. 2019, www.ncbi.nlm.nih.gov/pmc/articles/PMC6836141.
3. Antoni, Rona, et al. “Effects of Intermittent Fasting on Glucose and Lipid Metabolism | Proceedings of the Nutrition Society | Cambridge Core.” Cambridge Core, 16 Jan. 2017, www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/effects-of-intermittent-fasting-on-glucose-and-lipid-metabolism/8803CC1517F53CEF2BF8BFDC06A816D6.
4. Laurens, Claire, et al. “Is Muscle and Protein Loss Relevant in Long‐term Fasting in Healthy Men? A Prospective Trial on Physiological Adaptations.” PubMed Central (PMC), 20 Oct. 2021, www.ncbi.nlm.nih.gov/pmc/articles/PMC8718030.
5. Edinburgh, Robert M., et al. “Preexercise Breakfast Ingestion Versus Extended Overnight Fasting Increases Postprandial Glucose Flux After Exercise in Healthy Men.” PubMed Central (PMC), 14 Aug. 2018, www.ncbi.nlm.nih.gov/pmc/articles/PMC6293167.
6. Brun, Jean-Frédéric, et al. “Beyond the Calorie Paradigm: Taking Into Account in Practice the Balance of Fat and Carbohydrate Oxidation During Exercise?” PubMed Central (PMC), 12 Apr. 2022, www.ncbi.nlm.nih.gov/pmc/articles/PMC9027421.
7. Soliman, Ghada A. “Intermittent Fasting and Time-restricted Eating Role in Dietary Interventions and Precision Nutrition.” PubMed Central (PMC), 28 Oct. 2022, www.ncbi.nlm.nih.gov/pmc/articles/PMC9650338.
8. Kraemer, William J., et al. “Growth Hormone(S), Testosterone, Insulin-Like Growth Factors, and Cortisol: Roles and Integration for Cellular Development and Growth With Exercise.” PubMed Central (PMC), 25 Feb. 2020, www.ncbi.nlm.nih.gov/pmc/articles/PMC7052063.
9. Bachman, Jessica L., et al. “Exercising in the Fasted State Reduced 24-Hour Energy Intake in Active Male Adults.” PubMed Central (PMC), 21 Sept. 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC5050386

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