Does Working Out Break a Fast?

Does working out break a fast? The answer may depend on the type of exercise, how long you exercise, and what you eat before and after working out.


“Fasting” refers to an extended period of time in which an individual does not consume food or caloric beverages – usually ranging from 12-24 hours. In recent years, the practice of fasting has become popular for weight management, improved metabolic health, and extending longevity. However, a common question among individuals who adhere to an intermittent fasting diet is: does working out break a fast?

The answer is not definitively “yes” or “no,” as it depends on several factors such as: the type of exercise you are engaging in; how intense the exercise is; how your body and health are responding to fasting; and the length of time you have been fasting. For example, if you typically engage in high intensity interval training (HIIT) while intermittent fasting, but feel particularly run down during your current fast – it might be best to consider a lighter form of exercise such as yoga or walking. Conversely, people following a traditional ketogenic diet might find that rather than breaking their fasts, working out can actually help them optimize fat-burning and preserve lean muscle mass during their dietary restriction phases.

Therefore, if you are considering working out during a period of fasting – it is important that you assess both your mental and physical state before commencing any type of physical activity so that you can make sure your body remains healthy throughout the process.

What is Intermittent Fasting?

Intermittent fasting is the practice of eating for a set period of time during the day and then abstaining from food for the remainder of the day. This can be done daily or a few times a week, depending on the individual’s preferences. It is a popular diet trend because it is said to help aid in weight loss and increase longevity. Let’s explore what intermittent fasting consists of and if working out can break a fast.

Types of Intermittent Fasting

Intermittent fasting is a dietary strategy that involves cycling between phases of eating and periods of fasting. It’s becoming increasingly popular for those who want to lose weight, improve their health and feel better overall. Different types of intermittent fasting protocols vary in length and frequency so you can find one that works for your lifestyle, goals and preferences.

The most commonly known and practiced forms of intermittent fasting include:
-Time-restricted feeding: This involves restricting eating to a specific window of time each day, usually between 6-8 hours. This method is very popular as it’s easy to stick with – all you have to do is make sure to eat all your meals within this time period.
-Alternate day fasting: This type of intermittent fasting follows a pattern where you fast every other day or alternate between days where you’re consuming fewer calories than normal and days where you’re eating as normal.
-Whole day fasting: This type of intermittent fasting requires abstaining from calorie containing foods for an extended period, usually 24 hours or more at a time. This can be done daily, weekly or in any other combination according to the individual’s preference.
-The 5:2 diet: Also known as “the Fast Diet”, this requires five days a week with no restrictions on food intake followed by two nonconsecutive days of consuming 500–600 calories per day.

Does Working Out Break a Fast?

Working out while fasting is a popular trend practiced by lots of athletes, bodybuilders and everyday people who want to get in shape. The main argument for working out during a fast is that it will help you burn more fat and potentially lose weight quicker. But is working out while fasting safe and does it break the fast? Let’s look at the pros and cons of working out while fasting.

Intensity of Exercise

The intensity of exercise and type of activity you engage in when fasting will have an effect on the results. Moderate exercise such as walking, yoga, light jogging, or other activities may not break a fast; however, more intense activities—such as high-intensity interval training (HIIT) and heavy weightlifting—may require modifications such as supplementing with branch chain amino acids (BCAAs) or a small serving of carbohydrates. Weightlifting has been found to increase the production of stress hormones in the body which can alter insulin levels and promote gluconeogenesis (the creation of glucose). As such, these more intense activities can potentially interfere with the aims of fasting.

It is important to remember that individual response to exercise while fasting can vary greatly. Some persons may be able to tolerate higher-intensity exercises while others may need to be more conservative with their workout routine while they are fasting. Therefore, it is essential that individuals experiment on their own and find out what works best for them.

Duration of Exercise

The duration of your exercise session is an important factor when determining whether it will break your fast or not. In general, lower intensity exercises, such as a light jog or 30-minute yoga class are unlikely to impact your fast. High intensity aerobic activities, such as long-distance running or a HIIT workout, may break the fast depending on how long you are exercising for and how hard you are pushing yourself.

Exercising for short periods of time (15 minutes or less) is unlikely to break a short period of fasting (such as an intermittent fast). However, if you’re exercising for longer than this, the energy expenditure could be too great for your body to sustain itself without food and it’s likely that your fast won’t make it to the end without being broken. Therefore it’s important to weigh up your goals and decide if breaking the fast is necessary in order to achieve them.

On the other hand, if you’re engaged in a longer fast (such as water fasting), even low intensity exercises are likely going to have an effect someone’s energy levels and therefore might break their fast. It’s best to avoid exercise altogether while water fasting unless it is absolutely necessary – this might include exercises such as walking which don’t involve significant physiological strain.

Type of Exercise

When you fast, your body is relying on stored fats for energy, rather than carbohydrates and proteins that are derived from the foods you eat. Your body is able to access those fat stores when you fast and use them for energy. Therefore, when it comes to exercise while fasting, it is important to consider the type of exercise that you are engaging in.

Active forms of exercise (i.e., walking or aerobic activity such as jogging or cycling), often can be done while fasting without interfering with the benefits of fasting as long as they are low intensity. These types of exercises can help to speed up the breakdown of fat stores and require only minimal amounts of glucose for energy, which saltwater and other electrolytes help to supply.

More intense forms of exercise such as weight training and HIIT (high intensity interval training) will tend to cause a greater breakdown in the fats stored in your body. Additionally, these exercises rely on glucose as an important source of fuel which would require breaking your fast if they were performed while fasting. Therefore, it is recommended that more intense exercises be done post-fasting in order to reap their full benefits and maintain healthy blood sugar levels.

Benefits of Working Out While Fasting

Exercising while fasting is an increasingly popular form of intermittent fasting that can offer a range of physical and mental health benefits. There are various types of fasting such as time-restricted eating, complete abstention from food and certain nutrients, and alternate-day-fasting, all with different rules to break the fast.

The type of fast you are on will determine the answer to this question and what type of exercise would be appropriate. While working out while fasting appears to offer some benefits, doing so does require some precautions so that you don’t unduly overstrain your body or harm your health in any way.

The potential benefits gained from working out when fasting include increased fat burning, improved concentration and focus, increased levels of growth hormones which catalyze muscle production and fat burning, reduced inflammation throughout the body due to decreased insulin levels from reduced food intake, improved overall mental clarity due to increased growth hormone levels in the brain as well as elevated Ketone Bodies which act as a natural stimulant for cognitive function. There may also be other unknown physiological processes happening in our bodies due to exercise while in a fasted state.

Therefore, if you do decide to exercise while breaking a fast by working out, it is important that you listen to your body and adjust accordingly: Hydrate adequately before any activity – this is especially important when in the state of dehydration; start with low intensity aerobic movements such as walking or jogging; Moderately increase intensity gradually -limit extended periods of strenuous activity such as HIIT workouts or intensive weight training; Maintain constant awareness on breath rate: an indicator on whether you have sufficiently pushed yourself beyond what your body can handle safely; Incorporate rest days between workouts if necessary; Eat adequate protein after any workout -whether it be through meal or supplementation–for recovery.[1]

[1] Working Out While Fasting: What You Need To Know – Livestrong Fitness (

Risks of Working Out While Fasting

Working out while fasting carries certain risks and potential side effects that need to be taken into consideration. In general, it is not recommended to exercise during a fast as your body will not get the fuel it needs for high intensity exercise. While low-intensity exercises are generally safe, there is still potential for adverse outcomes, such as fatigue and dehydration.

When you attempt to work out while fasting, you will be relying on stored glycogen in order to fuel the effort; depending on your body’s own nutrient stores, this energy can last up to a few hours. If you overexert yourself or attempt high-intensity exercises while fasting, you may experience hypoglycemia (low blood sugar) due to lack of carbohydrates entering the blood stream. This can result in lightheadedness, dizziness or fainting, which is why it is important to stay hydrated and check your pulse regularly when exercising while fasting.

Additionally, due to lack of physical energy from no food intake before exercise, those that work out while fasted are at risk for dehydration and electrolyte deficiency. Make sure your hydration levels remain above 60%. During a long fast (over 24 hours), monitoring electrolytes such as potassium, magnesium and sodium should also be considered prior engaging in strenuous activity; all three will help regulate water balance within the body during intermittent or extended exercise periods.
Finally, even if you prepare tactically before working out while fasted by staying adequately hydrated and eating a meal shortly after completing your workout session; excessive fatigue can still occur after extended periods of exercise when not eating beforehand – so take breaks whenever needed and take caution when increasing training intensity or duration


In conclusion, whether working out breaks a fast or not depends on the type of fast being undertaken. Light exercise while fasting can help to make the process more comfortable and may even be beneficial. However, strenuous physical activity should generally be avoided during fasting as it can make it harder for the body to tap into its fat reserves for energy and make fasted workouts more difficult. It is important to remain within your own limits when engaging in exercise during a fast and ensure that you hydrate sufficiently throughout.

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