Is It Safe to Work Out While You’re Fasting?

The best time to exercise is always when you have a little bit of food and water in your body to fuel your system — but how can you do that if you’re fasting?

Athletic trainer Jennifer Dix, ATC, says there are ways to safely work out during a fast, whether you’re doing it for religious or health reasons. But you can’t treat a fast like it’s any other day, especially when it comes to physical activity.

“When you’re physically active while fasting, you have a much higher risk of dehydration and heat illness,” she says. “It’s something to be very cautious about.”

Is it safe to exercise while fasting?

It may be called a “fast,” but when you can’t have any food or water, it’s smart (and healthy) to take things slow.

“Physiologically speaking, the best and safest time to exercise is when you have the most hydration in your body,” Dix says.

During times when you can’t replenish water and nutrients, it’s best to preserve your limited energy. That means it’s best to schedule your workout before your fast begins or after it ends.

In figuring out whether it’s OK for you to exercise, the details of your fast make all the difference. Let’s break them down, shall we?

Exercising during intermittent fasting

Intermittent fasting is when you alternate between set time periods of eating and fasting. This type of fasting offers you more leeway to safely work out than religious fasts typically do.

“If you’re doing intermittent fasting for health reasons or weight loss, you can tailor your workout schedule to line up with your periods of eating and fasting in a safe and healthy way,” Dix says.

Can you exercise during a religious fast?

If you’re doing a religious fast, the rules are already written for you — but those rules vary depending on each faith tradition. And again, the details make all the difference in figuring out how to safely exercise while fasting.

Partial fasts involve eating less or abstaining from certain types of food. For example, on certain days associated with the lunar calendar, many Buddhists stop eating after their midday meal.

“Partial fasts are basically a type of intermittent fasting,” Dix says, “so it’s best to schedule your workouts during the times when you’re not fasting. This way, you’re able to eat and hydrate before and after physical activity.”

Things get trickier, though, when it comes to complete fasts — the kind where you abstain from all food and drink for a set timeframe.

Some complete fasts allow for drinking water, while others don’t. Here are some examples of the many types of religious complete fasts:

• Sunrise-to-sunset fasting: Some faith holidays require abstaining from food and beverages from sunrise to sunset, like the 30 days of Ramadan for Muslims or the Nineteen-Day Fast for Baháʼís. In these cases, fasters may wake up before sunrise or stay up until sunset to eat during permitted times.
• Overnight fasting: During fasting holidays like Yom Kippur and Tisha B’Av, people traditionally observe a 24-hour overnight fast abstaining from all food and drink. Jewish holidays begin at sundown and last until sundown the next day, so there’s no opportunity to eat breakfast in the morning.

Tips for working out while you’re fasting

Because there’s so little research on the topic, Dix cautions that many of the tips and guidance on physical activity while fasting — including her own — come from anecdotal experiences from athletes, coaches, nutritionists and others in the field.

She shares exercise tips for times when you’re fasting. But keep in mind that all of these tips vary depending on the rules and guidelines of the specific type of fast you’re doing.

Choose the right time for your workout

If possible, don’t exercise in the middle of your fast day. Instead, fit in your workout before your fast begins, or put it off until after your fast has ended.

“If you exercise before your fast starts, you’re able to work out and recover at a time when you’re still allowed to hydrate before, during and immediately afterward,” Dix says. The same is true of exercising after your fast ends, so long as you ease out of your fast the right way and hydrate before you hit the gym. (More on all of that in a moment!)

If you play a team sport, like if you’re a high school or college athlete, you likely don’t have a say in your training schedule — but that doesn’t necessarily mean you have to skip your workout while you’re fasting, Dix says. That leads us to our next point…

Eat healthy before your fast begins

If you’re doing a sunrise-to-sunset fast, like during Ramadan, it’s especially important that you don’t skip breakfast. And if you have a midday workout that can’t be rescheduled, like football practice, be sure to eat some extra protein in the morning before your fast begins.

“I recommend adding a protein shake to breakfast before your fast begins,” Dix says. “When you can’t eat during the day, it can be difficult to get in all the protein your body needs, especially for physical activity, so a shake can help supplement.”

What if you’re participating in a complete fast that doesn’t allow you to eat breakfast at the start of the day? In these cases, Dix says that it’s safest to avoid physical activity until you can break your fast and properly refuel.

Hydrate before and after (and watch for signs of dehydration)

Hydration is a key factor in working out, including how well you perform and how quickly you recover. When you can’t drink water during a fast, you risk health issues.

“There are risks to exercising when you can’t hydrate and don’t have any fuel in your system,” Dix warns. “You’ve got to be cautious and monitor yourself for dehydration issues.” Symptoms of dehydration include:

• Dizziness or lightheadedness.
• Headaches.
• Inability to focus.
• Muscle cramps.
• Nausea.
• Vomiting (in severe cases).

“To avoid these issues, be sure to focus on hydration during the times when you can eat and drink,” Dix advises. Water is the go-to way to do it, but certain fruits and veggies can help you hydrate, too. And it’s a good idea to skip that cup of coffee before a fast, as caffeine can contribute to dehydration.

Modify your expectations for your workout

When you’re exercising during a fast, your goal should be to get in a decent workout, not to bust through all your personal records for miles run or amount of weight lifted.

“Focus on the quality of what you’re doing, not the quantity,” Dix says. “If that last mile just isn’t feeling and you’re starting to stutter-step, just skip it.”

And if you’re doing a multiday fast, like during Ramadan, give your body some time to get used to its new eating schedule.

“It takes some time to adapt,” Dix notes.

Cool down after your workout

Sweating helps your body control its temperature — and that sweat needs someplace to go. “Our bodies need sweat to dry off in order to cool us down,” Dix explains. Here’s how to cool off quickly.

• Wear sweat-wicking clothing. Choosing the right clothing for your workouts can keep you from overheating.
• Change your clothes ASAP. This might sound like a no-brainer, but when you’re fasting, it’s more important than ever to shed your workout clothes after a sweat session, especially if you live someplace humid. “When it’s humid, sweat doesn’t dry, and it's just stuck there in wet, heavy clothing,” Dix explains.
• Rinse off in cold water. Dix says some people like to sit in an ice bath or take a cold shower to cool down after a workout, while others like to swish some water in their mouths and then spit it out. “That method doesn’t work for everyone, though,” she concedes. “When you’re fasting, it can just be too tempting.”

Listen to your body

We’ve already talked about how to prevent dehydration and the warning signs to look for, but there are other risks of fasting while exercising, too.

When it’s hot out, heat illnesses are common — and you’re at higher risk for them when you’re not well-hydrated. They include:

• Heat rash, little red bumps caused by sweat trapped in your glands.
• Heat cramps, painful muscle spasms that occur when your body loses nutrients.
• Heat exhaustion, when your body overheats and can’t cool itself down.
• Heat stroke, a life-threatening condition that happens when your body temperature rises above 104 degrees Fahrenheit (40 degrees Celsius).

Keep an eye on how you’re feeling and heed your body’s warnings and requests.

“If you notice that you're slowing down, getting bad reps or feeling clumsy, it’s really important to back off of your workout,” Dix stresses. “Dehydration- and heat-related illnesses can escalate very quickly.”

Choose the right foods to break your fast

If you’re planning to exercise after your fast has finished, don’t dig into heavy foods right away.

“Start hydrating and get a little bit of food in your body,” Dix advises. “You want to start giving yourself fuel without filling yourself up.”

These tips will help you make choices that will get your body get back up to speed, both literally and figuratively:

• Don’t chow down right away. You may be dying for a burger, but when you’re done with a fast and about to head into a workout, hold off on the heavy proteins and fibers.
• Pick a healthy snack. “Go for something small and light that will give you fuel,” Dix says. Hydrating, energizing foods like fruit, veggies and energy bars will give you healthy nutrients without making you feel stuffed.
• Water, water, water! You may be feeling sleepy after a day without food, but skip the energy drinks, juices and other caffeine- or sugar-laden options. After a day without water, they’ll only further dehydrate you.

Tell your child’s coaches

If you have a child who’s an athlete and is going to be doing an ongoing fast (like during Ramadan), Dix recommends letting their coaching staff ahead of time. Kids — even teens — don’t always have the self-awareness to know their limits or recognize when they’re starting to have issues.

“Make sure their coaches and phys ed teachers know they’re going to be fasting and can’t hydrate during that time,” Dix says. “This helps get another set of eyes on them during times of physical activity, from a health and safety perspective.”

Make sure it’s safe for you to fast

Before you begin a fast, it’s always best to touch base with a healthcare provider to make sure it’s OK for you. Fasting isn’t safe for people with certain health conditions, and exercising while fasting can quickly lead to health problems in people who are already at high risk.

If you’re told that you shouldn’t fast, you might feel some guilt or sadness about not being able to take part in this religious ritual. Talk to a religious leader you trust, like a member of the clergy, to ask what they recommend instead, so you can participate in your community’s customs without risking your health.