Fasting is a common practice in many cultures and religions, but it’s also become a popular practice for weight management and other health reasons. Fasting means you voluntarily reduce or abstain from food (and sometimes drink) for certain periods, which can vary from short intermittent fasting windows to prolonged durations. So many people wonder: Can you work out while fasting? More importantly, should you work out while fasting? Let’s explore what you should know about fasting and working out.

Types of Fasting and How They Affect You During Exercise

There are a variety of different types of fasting, and each has a different impact on you when you exercise. Here are the most common types of fasting and the effects of each kind of fasting and working out.

Intermittent Fasting

Intermittent fasting involves alternating periods of eating and fasting. This can include time-restricted eating, alternate-day fasting, or periodic fasting. In some cases, people restrict their eating to a specific period each day, fasting for the other hours of the day. In other cases, people go back and forth between eating normally on some days and fasting on others. 

How it impacts exercise: Because you choose when you eat and when you fast, intermittent fasting and working out can function well together. You can choose to exercise after you’ve eaten and have energy rather than after periods of fasting. 

Spiritual or Religious Fasting

Many faiths participate in fasting at specific points during the year. In some cases, people don’t eat or drink at all during certain parts of the day, while in other cases, people simply restrict certain types of food for a set period. 

How it impacts exercise: People restricting only certain foods should be able to exercise normally. People who can’t eat or drink anything during certain hours of the day will experience depleted energy and should exercise with lower intensity before fasting hours begin so they can replace lost calories and hydration. 

Prolonged Fasting

Prolonged fasting means significantly reducing your caloric intake for two consecutive days or more. Prolonged fasting longer than 20 days comes with serious risks to your heart. Even prolonged fasts under 20 days can result in significant loss of electrolytes and muscle mass, along with other potential health complications. 

How it impacts exercise: Because prolonged fasting already impacts your body significantly, take it easy and refrain from any high-intensity exercise. Studies show that after prolonged fasting, the ability to sustain intense aerobic exercise is reduced considerably.

Which Type of Fasting Works Best for Exercise?

Can you work out while fasting, regardless of the type? Possibly, but an intermittent fasting workout is your best bet, which offers the most flexibility with your eating schedule, so it works best for fasting while working out. That means well-timed intermittent fasting exercise won’t feel quite as brutal. 

When should you work out while fasting? Should you work out after fasting or before? Exercise before your fasting begins, when you’re hydrated and still have caloric energy, or after your fasting ends when you’ve had a chance to replenish your calories and hydration. If possible, integrate post-workout foods that help your body recover, too. 

No matter what, adjust your expectations while fasting. You can work out while fasting, but your energy and endurance will be reduced, so give yourself grace and don’t overdo it.

Is It Safe to Work Out on an Empty Stomach?

For most people, it’s fine to work out on an empty stomach, but you may experience lethargy, wooziness, or light-headedness due to low blood sugar. You’ll get tired faster, too. While some older studies indicate that exercising in a fasted state can burn more calories, other studies have failed to show these advantages, so it may not be worth it. 

Is it best to eat before or after a workout? Generally, it’s best to eat something before exercising. For people over the age of 55, it’s essential. Otherwise, there’s a risk of muscle loss, which is already an issue for many people over 55. 

Signs That You Shouldn’t Work Out While Fasting

Listen to your body while fasting. It will communicate whether fasting and working out are safe for you. If you experience any of the following signs, it may indicate dehydration or heat exhaustion, which suggests fasting while working out doesn’t agree with you:

• Dizziness
• Extreme sweating
• Fainting
• Headache
• Inability to maintain coordinated movements
• Low blood pressure
• Mild and temporary confusion
• Muscle cramps
• Nausea, diarrhea, or vomiting
• Pale skin
• Rapid breathing
• Rapid heartbeat

A Balanced Approach to Fasting and Exercising Effectively

Can you work out while fasting? Most likely, as long as you do the following:

• Take it slowly and carefully. While fasting, you should lower the intensity and frequency of your workouts.
• Adjust your timing. Integrate workouts before your fast begins or after it ends, and you’ve had time to eat and drink. Exercising on an empty stomach won’t hurt most people, but it also won’t feel particularly good. Your energy will be much better if you can wait to exercise until after you’ve been able to replenish your stores.
• Listen to your body. If your body tells you that exercising while fasting is too much—stop. You may need time for your body to adjust, or you may need to wait to exercise until you’re finished fasting.