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Home arrow Nutrition arrow Intermittent Fasting arrow Working Out While Fasting: How To Do It Safely

Working Out While Fasting: How To Do It Safely

Written by Edibel Quintero, RD
Fact checked by Rosmy Barrios, MD
Last update: October 21, 2023
7 min read 1348 Views 0 Comments
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Intermittent fasting induces a caloric deficit by restricting when you can eat, but if you want to increase this deficit, you might try working out while fasting. In this article, we’re going to take a look at fasted workouts, how they can be done safely, and if they work.

working out while fasting

Intermittent fasting is a dieting method that involves a fasting period and an eating window. Many people have successfully used this method to reduce body fat and overall weight loss. Those using this method may also engage in exercise to boost their weight loss.

Regular exercise can help you to burn more calories each day, which, in turn, helps you to lose weight more quickly. When following an intermittent fasting method, you may be wondering if exercise while fasting is safe.

In this article, we’re going to look into exercise while fasting, fasted workouts, and how you can safely exercise while on an intermittent fasting plan. To learn more, keep reading.

Working Out While Fasting – Is It Safe?

It is safe to work out while fasting; the key is to listen to your body. Fasted workouts can be done safely, provided you are not pushing yourself too hard, you’re keeping yourself hydrated, and you eat the right macronutrients after your workout to restore your health.

Working out while fasting can help to promote fat burning and increase muscle mass, provided it is done properly. If you are undertaking longer fasts, it is worth sticking to low-intensity workouts to preserve your energy needs. Shorter fasting styles include the 12-hour fast, the 14:10 method, and the 16:8 method.

It is also important to note that some people do not want to work out while fasting, and this is okay. If you find you become too exhausted by workouts during fasting, do not continue them.

If you are planning on engaging in high-intensity interval training, or another high-intensity workout, then you need to ensure you eat a nourishing meal before you do it. This is so that your body has enough glycogen stores to tap into for fuel.

If you’re considering starting an intermittent fasting plan but don’t know where to start, you could take a look at the DoFasting app. This app provides a space for you to track your calories and your fasting periods, and it will even give you a reminder of when to start your fast each day.

On top of this, you’ll also find tons of workouts that are suitable for your fasting period and can help with burning fat and improving muscle tone.

How to work out safely when fasting?

Working out safely while fasting requires a few different things, including eating correctly during your eating window, keeping your electrolytes in balance, and staying hydrated. All of these aspects will ensure that your workouts burn fat and increase weight reduction.

You need to eat meals that include all macronutrients, including protein which will support muscle repair. You will also need to consume starchy carbs to ensure your body has enough glycogen stores to sustain you through fasted workouts.

Staying hydrated is absolutely essential. As you get a lot of water from the food you consume, you are in more danger of becoming dehydrated when working out on an empty stomach. This is why you need to ensure that you consume enough water – more water than normal, in fact – during fasted workouts.

You will also need to keep your electrolytes in balance. Commonly, people will do this by consuming sports drinks when exercising. However, sports drinks and carbohydrate-electrolyte drink products contain lots of sugar and will break a fast. Instead, you could try consuming electrolyte mixtures.

You may also want to engage only in low-intensity exercises. This could include walking a few miles during a fast, practicing restorative yoga, or light jogging as opposed to running.

When To Workout During Intermittent Fasting?

Most people recommend that you should work out just after waking up, during an intermittent fasting plan. It is best to do it at this time as it fits in with your natural circadian rhythm.

There is some evidence that waiting to eat after workouts can help to enhance the level of human growth hormone in the system. Fasting has been shown to stimulate human growth hormone secretion and, by increasing this, it helps to keep your body in a fat-burning state.

It is important to note that you may experience a drop in performance when you first begin exercising on an empty stomach. It can take a while for your body to adapt to using fat as a fuel source, meaning your exercise performance could drop.

Some forms of aerobic exercise may be more suited to working out than others. For example, going on a daily walk during a fast could help you to burn more calories while not exhausting yourself.

Pros And Cons Of Working Out While Fasting

There are pros and cons to working out while fasting. We’ve summarized each of them below.


The pros of working out during fasting periods include:

  • May increase fat oxidation – Due to the depleted state of glycogen stores in the body during a fasted state, fat is more readily used for fuel. This enhances fat metabolism, fat loss, and overall loss of weight.
  • May boost long-term performance – Working out in a fasted state is thought to help your body to adapt to burning body fat for fuel. It can also help to train your body to continue working out, even with low blood sugar. Additionally, working out in the morning may increase the amount of oxygen our muscles can use, though research on this is patchy.
  • Could increase autophagy – Autophagy literally means ‘self-eating,’ and is the process by which your body’s cells are recycled and removed from the body. This process helps to replenish cells and get rid of damaged ones and decreased autophagy has been linked to a number of chronic conditions.
  • Could help slow the progress of aging – Research suggests that the combination of fasting and exercise can actually help to slow the aging process and the progress of some diseases.
  • May improve insulin sensitivity – There is some research that suggests consistent workouts in a fasted state can improve insulin sensitivity. As one of the key factors in the development of prediabetes and type 2 diabetes, a decrease in insulin resistance can have a profound impact on blood glucose levels and overall health.


The cons of fasted exercise include:

  • May not be consistent – Due to the depleted glycogen levels in the body during fasted workouts, your body turns to fat for fuel. However, this can lead to drops in sustenance, meaning your workout intensity may not always be consistent.
  • Could lead to dangerously low blood sugar – Due to the already lowered levels of blood glucose, exercising can cause a further drop. Low blood sugar can lead to fainting and dizzy spells.
  • May be more difficult to build muscle mass – There is some research that suggests that men who participated in both intermittent fasting and exercise did not build as much muscle when exercising on an empty stomach as those who were not fasting. If you are aiming for muscle gain IF may not be for you.
  • Could result in muscle degradation – Exercising too hard while fasting could actually lead to the breakdown of muscles.

Weight Lifting And Intermittent Fasting

Contrary to popular belief, strength training, and intermittent fasting can work together. While most of the focus of IF is on weight reduction and caloric intake, there is no reason you can’t conduct your normal strength routine while on an intermittent fasting plan.

While research rarely shows significant muscle gains for those on an IF plan, when done safely, weight lifting can help you maintain muscle mass during an IF diet. However, if you are looking to build muscle, IF may not be for you.

Many studies have shown that intermittent fasting doesn’t allow for enough of the bulking required to build muscle and so, it is not suitable for anyone who is dedicated to building up muscles. Instead, it should be used by those looking to reduce weight while still maintaining toning.

Another time when IF may come in handy for those who weight lift is during cutting periods. During cutting, you aim to eat at a reduced calorie intake which IF can help with. Due to the shortened periods in which you’re allowed to eat IF can help you to cut calories easily.

IF also comes with many other health benefits, making it a good choice for cutting periods.

Cardio And Intermittent Fasting

A cardio session during intermittent fasting, especially one done in the morning just after you wake up, is thought an effective method of boosting fat loss. Doing cardio exercise while fasting is thought to ensure that the body burns fat for fuel as glucose levels are depleted.

While research says that both exercising in a fasted state and exercising after eating can improve metabolic activity, there is a chance that more fat is burned during fasted cardio as your glycogen levels are depleted.

Though research for fasted cardio exercise suggests it can help with weight loss and may have other benefits for insulin levels and body composition, most research does show that there are very limited differences between calories burned during non-fasted workouts too.

In fact, there is some evidence that fasted cardio may actually lead to muscle loss, and lower intensity cardio is suggested to avoid this. In addition, due to lower blood sugar levels, your exercise intensity may falter throughout the period.

It is important when trying out fasted cardio to ensure that you hydrate properly as dehydration can occur more easily when fasting. You may also want to consider meal timing before high-intensity activities. This is because lower levels of glycogen can lead to exhaustion more quickly.

While exercising in a fasted state can provide many benefits, it is not necessary for calorie burning and weight reduction. It is more important to eat at a caloric deficit and ensure you move more each day.

A Word From Our Nutritionist

Intermittent fasting is a weight reduction method that involves fasting and feeding windows. It helps people to lose weight by reducing the time people can eat and, therefore, enforcing a caloric restriction.

Fasting also induces a state of ketosis in the body. This metabolic state is when the body burns fat for fuel rather than blood sugar. The elevated fat metabolism during this state is another way this dieting method helps healthy subjects to lose weight easily.

While the caloric deficit and ketosis state both help to reduce weight, people using the IF method may also want to increase the caloric deficit by exercising more. Due to the restrictive nature of the method, finding a time to exercise during the eating window may be a little difficult, leading to fasted training.

While some people recommend avoiding physical activity during fasting windows, there is no reason you cannot work out during this period. In fact, some research suggests you may burn more fat during fasted workouts.

While fasted workouts are not suitable for everyone, namely though who engage in heavy lifting for muscle building and endurance athletes, for the average person looking to lose weight and more fat, a fasted workout could be useful.

It is important to take precautions when engaging in fasted workouts. These include ensuring you are properly hydrated as well as keeping your electrolytes in balance. You should also ensure you’re eating enough protein during your eating window for proper muscle repair after exercise.

It is also important to note that it may take a few weeks for your body to become fat adapted, meaning your workout intensity could suffer as your body adjusts to burning fat for fuel during physical activity.

Fasting is a very good weight reduction method that has been shown to help people to reduce weight quickly. In addition, it is thought to reduce your risk of a range of health conditions. If you’re considering trying it out and are concerned about how it could affect you, speak with a healthcare provider.

Note: during fasted workouts, if you ever feel dizzy or feel weak, you should stop immediately.


Fasting and exercising can work together to help you to burn more fat and achieve your fitness goals. If your primary goal in intermittent fasting is losing weight, then fasted workouts can be helpful for you.

If you’re looking to try intermittent fasting but don’t know where to start, check out the DoFasting app. It can help you to find a suitable method of fasting and provide a space for you to track your calories and weight.

Written by Edibel Quintero, RD
Edibel Quintero is a medical doctor who graduated in 2013 from the University of Zulia and has been working in her profession since then. She specializes in obesity and nutrition, physical rehabilitation, sports massage and post-operative rehabilitation. Edibel’s goal is to help people live healthier lives by educating them about food, exercise, mental wellness and other lifestyle choices that can improve their quality of life.
The article was fact checked by Rosmy Barrios, MD
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Written by Edibel Quintero, RD
Fact checked by Rosmy Barrios, MD
Last update: October 21, 2023
7 min read 1348 Views 0 Comments

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