Should you work out while fasting?

Group workout class

For those interested in maximizing their fat-burning potential, why not try working out while fasting to help make the most out of each exercise? Here’s what fitness buffs should know about fasting while working out.


The FAQs About Working Out While Fasting


Working Out While Doing Intermittent Fasting

A study from the FASEB Journal says this combination can “enhance the ability of aerobic exercise to increase endurance” once the body makes the switch from using carbs as fuel to fats instead.

The key to gaining muscle and losing weight is counting calories and exercising, and hormone optimization.

This has to do with the depleted stores of glycogen the body holds. This forces the body to up its production of growth hormones and testosterone.

Daily intermittent fasting alone already holds a ton of benefits. However, combining it with cardio exercise or strength training takes those benefits to a whole new level.

The increase in growth hormones and testosterone causes the body to burn fat more efficiently and develop and repair muscles quicker.

Try not to dwell on calories in and calories out, fearing muscle loss. Working out while fasting is not only safe, but it is actually one of the best ways to improve your health and body composition.



Anyone who exercises will most likely want to know how to get the most of each workout in the shortest possible time. This is one of the reasons you should start working out while fasting.

Among the many benefits, exercising while intermittent fasting forces the body to shed fat.

The body’s sympathetic nervous system (SNS) controls its fat burning process. This process, in turn, is stimulated by exercise and a lack of food intake.

One of the reasons you should work out and fast is because combining the two maximizes the impact of catalysts and cellular factors. These things force the body to break down fat and glycogen for energy.

Fasting before exercising can reduce both body weight and body fat. This is in contrast with workouts after a meal, wherein reductions were found only in body weight.

A study published in Cell Press demonstrates how prolonged fasts also cause the body to regenerate its entire immune system. As a result, it repairs damaged DNA, limits diseases that happen with age, and generally prolongs life.

The study further details how fasting triggers the pancreas to regenerate itself. This improves the ability of the body to control the levels of blood sugar levels – resulting in fewer cravings for sweet treats!


Cardio While Intermittent Fasting


When performing fasted cardio, you should choose high-intensity interval training (HIIT) for maximum effects.

HIIT involves as little as four to five minutes of intense activity. Often, people do this for as little as 30 to 45 minutes at a time.

One of the many benefits of HIIT is that it’s time-efficient. It also provides a higher fat burning rate, boosts human growth hormone (HGH) production, increases testosterone levels, improves body composition, boosts brain function, and even helps combat depression.

However, keep in mind that those new to working out while fasting may experience a slight drop in performance at first. This is because the body might need a bit more time adapting to fat as its new source of fuel instead of glucose.

To further increase the benefits of working out while fasting, you should continue to fast about two to three hours after a bout of cardio. This promotes a rise in your HGH levels, which then raises the body’s fat-burning abilities.

You should always avoid cardio on a full stomach. The body’s sudden demand for blood flow to supply oxygen to the muscles steals that blood flow from the digestive system, which the body needs to properly digest food and absorb nutrients, leading to cramps and stitches.


Lifting Weights While Fasting

Group of people running

You can perform strength training exercises in a fasted state but bear in mind the role glucose plays in repairing muscles after an intense strength training workout.

Unlike HIIT cardio, heavy lifting puts enough stress on the body to call for a meal immediately after the workout.

That meal should include fast-assimilating protein, like whey protein. A serving of at least 20 grams of protein within 30 minutes after a workout should do the trick.

For some people, strength training exercises may be hard to perform on an empty stomach. These people are usually more sensitive to changes in the levels of blood sugar in their body.

They may experience nausea, dizziness, lightheadedness, or faintness, often within the first 15-25 minutes of the workout from the decline in blood sugar levels in their bodies. In such cases, a quick whey protein shake can also function as a beneficial pre-workout meal. In short, lifting while fasting may not be for everyone. 


Best Time to Work Out While Fasting

Man working out at the gym with cables

The best time to work out while fasting is in the morning upon waking up and before breakfast. Often, this is just before the end of the intermittent fasting period.

One of the biggest myths about working out while fasting is that it leads to muscle loss. People assume that the body lacks the carbohydrates and glucose (sugar) it needs for a morning session without food intake.

This view believes that not eating before a workout forces the body to break down muscle protein to get the energy it needs. In reality, the body actually stores glucose or sugar in the liver and muscles in the form of glycogen.

Throughout the night, the insulin levels (the hormone that helps process sugar and burns fat) in the body, along with glycogen in the liver, decrease, so the body still has the glycogen stored in the muscles.

On that morning workout, the body gets the energy it needs from the glycogen stored inside the muscles.

As one continues to work out, the body burns through that supply of glycogen or carbohydrates. Afterwards, it is forced to turn to a different supply of energy, which it finds in free fatty acids.

Working out while fasting is best done in the morning as it supports the body’s natural circadian rhythm. Exercising or eating too close to bedtime tends to interrupt the levels of deep and rapid-eye-movement (REM) sleep, both of which are necessary for rest and recovery.


Working out while fasting is a safe and effective way to burn more body fat, but it goes without saying that it is best to start slow with the exercises while your body is adapting and gradually increase the intensity later on.

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