Last Updated on November 9, 2023 by Fasting Planet
You always strive to take the best care of your health, which is why you maintain a nutritious diet and exercise regularly. Lately, you’ve started to get into fasting as well. You’ve now worked your way up to a longer fast, but you’re not sure how to incorporate physical activity. Can you work out on a fast or not?
Exercising while fasting is safe for most people. While you could increase your body’s fat-burning capabilities, but there’s a careful line to be walked here. By pushing yourself too hard or exercising for too long, you could end up ill and unable to complete your fast. Also, some research purports that you could lose muscle when exercising on a fast, depleting this more than fat.
If you’re interested in exercising while fasting or at least learning more about it, this is the post for you. In it, we’ll cover exercise guidelines for all different types of fasts, discuss whether you burn more muscle or fat, and talk about what kind of weight loss results you may expect. You won’t want to miss it!
Exercising While Fasting: Should You Do It?
While exercising on a fast is generally okay, you still want to be as safe and smart about it as it you can. Never begin a physical fitness regimen when on a fast without speaking to your doctor first. In most instances, stick to low-intensity over high-intensity exercise.
Listen to your body as well. If you start to feel sick, weak, or woozy, you need a sports drink and maybe even more calories than that. You also must drink water to avoid dehydration.
Now, certain types of fasts may prohibit some of the above. That’s why we now want to delve into all the fasts you may try and discuss whether you should exercise when on them.
Exercising While Water Fasting
A water fast is one in which you only consume water. Depending on the length of your fast then, exercise may or may not be the best idea.
For example, if you’re fasting for 24 hours straight, then skip the exercise or stick to very low-intensity fitness like yoga. You’re likely already pretty hungry on a water fast, and exercising could make you hungrier.
Also, although water is very good for you, it’s lacking in electrolytes. Good, ol’ H2O contains some electrolytes, but not in the quantities you’d need after a tough sweat session. Instead, you should sip a sports drink or eat foods with calcium, magnesium, potassium, chloride, and/or sodium, neither of which you can do while water fasting.
If you’re only on a water fast for a few hours a day, then feel free to exercise when you’re not fasting.
Exercising While Intermittent Fasting
Water fasting is one type of intermittent fast, in which you fast for some hours or days and then not on others. You may intermittent fast on the following schedules:
- Spontaneous meal skipping: You’d omit breakfast and then eat lunch or dinner on a spontaneous meal skipping fast, or do some other combination of the above. Whatever works for you, really, is how you should fast.
- The Warrior Diet: Under the Warrior Diet, you skip food all day and then eat a sizable meal at night.
- Alternate-day fasting: We’ve discussed alternate-day fasting on this blog. It involves you fasting for one 24-hour period then eating for the other, alternating days throughout the week.
- Eat-Stop-Eat: The Eat-Stop-Eat diet is similar, but better for beginners since you’re only fasting two times weekly max.
- The 5:2 Diet: You may also try the 5:2 Diet, in which twice a week, you consume no more than 600 calories for men and 500 calories for women. The other five days of the week, you can eat as you regularly do.
- The 16/8 Method: Another popular type of intermittent fast is the 16/8 Method, in which you spend 16 hours of the day fasting and eight eating. There are variations of this intermittent fast that change the allotted time for eating and fasting.
Since few of these intermittent fasting types involve you giving up food altogether for too long, you’re generally safe to exercise. If you are fasting for up to 24 hours at a time, such as on an alternate-day fast, then save your exercise for the days you’re eating more.
Exercising While Juice Fasting
A juice fast operates much like a water fast, instead of drinking only water, you consume fruit and vegetable juices. These fasts may last up to three consecutive days, or, like a water fast, you can juice fast off and on in smaller time increments.
While juice does contain calories to fuel your exercise, not all juices are suitable for restoring your electrolytes. If you’re going to engage in some fitness during a juice fast, make sure you consume tart cherry juice or orange juice. These can add to your body’s supply of phosphorus, magnesium, and potassium.
Exercising While Dry Fasting
A dry fast is one in which both water and food are prohibited. Unless you’re only doing this fast for a few hours a day, then it’s not very safe to exercise on a dry fast.
Exercising While Prolonged Fasting
If you’re thinking of exercising while fasting for 36 hours or longer, known as prolonged fasting, you should be okay. In fact, a bit of light exercise may allow you to maintain your muscle mass as you torch fats for energy. The keyword here is light exercise, as anything too strenuous could leave you dizzy and irritable.
Exercising While Fasting on Ramadan
The Muslim observance of Ramadan requires daily fasting for 11 to 16 hours, or from sunup to when the sun sets. At nightfall, Iftar or fatoor is consumed, which is a meal that breaks the fast for the day.
Schedule your exercise around Iftar, either right before or a few hours after the meal wraps up.
Do You Burn Muscle While Fasting and Exercising?
Your body gets its energy primarily from glycogen, which is stored up in the body to keep us moving. When that fuel source depletes, the expectation is your body will begin burning fat for energy next. Yet sometimes, that’s not what happens. Instead, your body starts chipping away at your muscle mass.
Sometimes, it’s hard to tell this happening, but there are a few signs to look out for. If you feel unusually exhausted, even when fasting, your muscle mass could be disappearing. You’ll notice fatigued muscles that don’t work as well as they typically do.
You may also drop an incredible amount of weight very quickly while fasting. A standard scale will not tell you where this weight loss is coming from, so make sure you have one that can track your muscle mass and body fat percentage. If your muscle mass has decreased but your body fat hasn’t, something’s wrong.
To torch body fat instead of muscle while fasting and exercising, you must first prioritize your sleep. By not getting at least seven or eight hours of sleep nightly, hormonal levels can change, which can take any carbs you eat and send them straight to fat storage. On top of that, the growth of your muscles inches to a crawl.
Also, avoid sitting around and doing nothing. Mark’s Daily Apple really advocates for exercising during fasting. He says to stick to simple cardio and weightlifting to maintain your muscle. If you don’t use it, you will lose it.
Exercising While Fasting to Reach Ketosis: How Long Does It Take?
Ketosis is a desirable state for many fasters and dieters. Once your body has no more glucose to burn, it will start torching your stored fats, as we said. When this happens, your ketone bodies increase, which keep up the energy needed to burn more fat.
The time it takes to enter ketosis varies, anywhere from two to four days or more. If it takes you longer than four days to reach a state of ketosis, that just means you had so much glucose in your body that it took a long time to get rid of it.
It’s possible to speed up the ketosis process in a few ways, some of which we can help and others we can’t. For example, how much fat, proteins, and carbs you consume will make it easier or harder to enter ketosis. Exercising can help us make more ketone bodies, as can having a fast metabolism. As you get older, reaching a state of ketosis may take longer no matter if you do the above.
Does Exercising While Fasting Help You Lose Weight?
Entering ketosis, as you may have figured, is like opening the door to weight loss. In burning body fat, you look trimmer and slimmer.
Also, by restricting your calorie consumption through an intermittent fast, you may burn more calories than you eat. Since that’s necessary for weight loss, you could lose a few pounds.
Exercising torches calories as well, which can lend itself to your weight loss efforts. When you combine the two, do you lose more weight exercising while fasting?
You can, but the results vary. For example, if you’re extra hungry after not eating much and sweating it out, you may feel inclined to eat more the next time you can. You’d have to practice intermittent fasting regularly and get in touch with your self-discipline, really sharpening it to prevent these bouts of overeating. Otherwise, you could actually gain weight.
By tracking your calories when you do eat and keeping your portions low if you have to, then it’s possible to lose more weight through fasting and exercising. Do know that it’s often a long haul to reach the results you want, not an overnight climb, as you’re doing lower-intensity workouts.
If you have the patience and the drive though, you could achieve a slimmer you through intermittent fasting and exercising.
Does Exercising While Fasting Elevate Blood Glucose?
Your body’s level of blood glucose, also referred to as blood sugar, is something you can’t afford to ignore as a diabetic. Even if you’re at risk of being prediabetic, it pays to track your blood glucose.
As we’ve discussed on this blog, when blood glucose rises too high, you develop hyperglycemia. Blood glucose can increase without sufficient levels of insulin as well as from the consumption of processed foods, both of which may lead to hyperglycemia.
Hypoglycemia occurs if your blood sugar drops too low. While those with diabetes are more likely to have hypoglycemia, since you’re not providing food or glucose to the body, low blood sugar is something intermittent fasters need to keep in the back of their minds as well.
What if you’re exercising while fasting? Does your blood glucose go up or down? According to a classic study in the Journal of Applied Physiology, when nine male participants exercised and fasted for about 24 hours, “plasma glucose was elevated by exercise in the fasted trial but there was no difference between fed and fasted during exercise.”
The researchers concluded that blood glucose won’t change either way–increasing or decreasing–when exercising and fasting. That’s even though liver glycogen does dwindle during your fast.
Does Exercising While Fasting Trigger Metabolic Adaptation?
We also want to discuss metabolic adaptation in relation to exercising and fasting. Metabolic adaptation, sometimes referred to as a starvation response, is the body changing how well it can make food into energy. When our bodies reach close to starvation conditions, such as during an intermittent fast, we don’t immediately use those calories we have for energy. Instead, they get stored for later.
Metabolic adaptation goes hand in hand with total daily energy expenditure or TDEE. This includes our exercise activity, thermic effect of food, non-exercise adaptive thermogenesis, and basal metabolic rate. The basal metabolic rate is very important, as it comprises our TDEE by about 60 percent.
What is a basal metabolic rate? It’s how many calories we need to consume for our bodies to continue functioning biologically. Our thermic effect of food, or how much energy it takes for a macronutrient to break down, is up to 15 percent of our TDEE, so it’s crucial, too.
Your TDEE begins to drop once you enter metabolic adaptation because your body isn’t sure if it’s starving or not. This means your body naturally moves less (non-exercise adaptive thermogenesis) and your basal metabolic rate slows. The thermic effect of food alters as well in that we don’t have as many calories for macronutrient breakdown.
While exercising during a fast can induce metabolic adaptation and even cause weight loss, it can be double-edged sword. In some instances, that person can continue eating the same number of calories, but their weight no longer comes off. This is because your body’s TDEE learns to adapt to the calories you’re consuming, even if they’re fewer than before. As your metabolism catches up, you’d have to drop even more calories for weight loss.
Tips for Exercising While Fasting
If everything you’ve read to this point has convinced you to exercise on a fast, make sure you keep these tips in mind.
- Know the best times to exercise while fasting: There are certain times during an intermittent fast that are better for exercise than others. Right when you wake up is one great time to get your fitness on, as is about an hour after waking. This activity works best with your circadian rhythm, which can be disrupted if you exercise too late into the day. Considering it can be hard enough to sleep on an intermittent fast as it is, at least when you’re new to it, don’t do anything that can ruin your shuteye.
- Try cardio: According to this video by Thomas DeLauer, cardio is a great physical activity to do when fasting. He cites studies that mention how our body’s lipid oxidation and beta oxidation change while doing cardio on a fast. Your body may rely on fats for energy two to three times more than usual, torching your fat at a high rate.
- Make sure you’re getting your weightlifting in: Again, this will preserve muscle mass and keep you looking buff. Mark’s Daily Apple suggests you avoid maxing out with your weightlifting. Instead, do a few high-intensity reps, but fewer than usual.
- Try burst training: Sort of akin to the shorter reps of high intensity recommended by Mark’s Daily Apple, burst training involves high-intensity activity followed by rest. As an example, you might exercise intensely for up to four minutes and then take a 20-minute break.
The Dangers of Exercising While Fasting
If you have the approval of your doctor, then we do advocate for exercising while fasting. That doesn’t mean there aren’t negative effects for some people, though. Here are some dangers to look out for if you work out during a fast.
Losing Muscle
Yes, we had to touch on this one more time because it’s such a major issue. Your body needs energy, and the proteins in your muscles can be used for exactly that. Unless you actively combat it, you could end up with smaller muscles after an intermittent fast in which you exercise.
As we said before, when stepping on just a regular scale, this will look like weight loss, but you’re actually losing muscle more than fat.
Possibly Slower Metabolism
According to Columbia University nutrition educator Priya Khorana, EdD, who spoke to Healthline.com, with less energy and fewer calories to go around, your metabolism could end up slowed down by exercising during a fast.
This goes back to what we talked about in the section about metabolic adaptation. Your body will do its best to keep you alive when it believes you’re starving. While a certain number of calories may be sufficient for weight loss at first, eventually, you have to keep lowering that number to continue losing weight. This is unhealthy behavior.
Potentially Worse Physical Performance
This one goes both ways. Some fasters say that exercising while intermittent fasting makes them perform better, but you could just as well do worse. After all, you don’t have the energy you typically rely on to fuel your workouts. This may make you feel sluggish and unable to work with as hefty weights as you usually do.
Conclusion
Exercising on an intermittent fast can be safe if your doctor permits it. There’s the potential for weight loss as your body burns through fat after using all its glucose reserves. You also must be aware of the downsides, which involve a decrease in performance, feeling dizzy or sick, slowing down your metabolism, and burning more muscle than fat.
Only you can decide if you want to continue working out while exercising, but if you do, be safe, smart, and listen to your body. Best of luck!