Everything You Want To Know About Intermittent Fasting And Exercise

The Bottom Line

Fasted exercise burns more fat, improves glucose metabolism, boosts mitochondria function, and improves lipid profile.

Summary

Fasted exercise is simply working out without eating for a prolonged period before. Fasted means nothing but water, black tea, and black coffee for 8 -12 hours before working out. Now, why would anyone put themselves through this? Working out is hard enough. I am with you, but if you are going to put effort into working out, don’t you want to get the most out of it?

Optimizing the benefits of working out is where a fasted workout comes in. While it will not improve your performance, it will help you burn more fat and improve your metabolism while lowering your risk of diseases such as type 2 diabetes and cardiovascular disease.

There are four critical factors to look at when it comes to disease risk, metabolic health, and weight loss. These critical factors are fat oxidation, glucose metabolism, mitochondria function, and blood lipid profile. If all of these are in tip-top shape, you are on your way to a long and healthy life. Furthermore, intermittent fasting and working out just so happen to improve all four of these critical factors.

Increased Fat Oxidation

Put simply; this is your body burning fat as fuel. Burning fat as fuel is an essential part of a healthy metabolism and a good thing if you want to lose weight. While any exercise (either fed or fasted) will increase fat oxidation, fasted exercise can increase fat oxidation for up to 24 hours after your workout is over. That means you will be burning fat long after you wash the sweat off. There are two reasons for this. First, when you don’t eat before a workout, your body only has two fuel choices, stored fat, and glycogen. When glycogen is used up, your body will prioritize burning fat as fuel since the amount is much more plentiful (Aird et al. 2018). Second, intermittent fasting before working out keeps insulin levels low, which allows stored fat to be released from fat cells and used as energy to fuel your workout.

Improved Glucose Metabolism

Glucose metabolism is the system that maintains your blood sugar level. It is also the system that malfunctions in diabetes. Maintaining a healthy blood sugar level is essential for overall health and longevity. There are two primary components to look at with glucose metabolism; blood glucose (or blood sugar) levels and insulin levels. Ideally, you want both to remain steady around the healthy range. Stable blood glucose and insulin levels are both linked to longevity and better overall health.

Here’s how it works. When you eat carbohydrates, your pancreas releases insulin. Insulin is a hormone that signals to your cells to take up glucose from the bloodstream. This uptake of glucose into the cell lowers the level of glucose in the blood and allows for the cell to use the glucose to produce energy.

When circulating insulin levels are high, your body is in energy storage mode, and fat cannot be released from fat cells and used as fuel, which prevents you from losing weight. Low insulin levels are one reason fasted exercise increases fat oxidation; there is no insulin present to stop your fat cells from releasing fatty acids to be used as fuel, helping you lose weight. Furthermore, increased fat oxidation can further improve insulin sensitivity (Vieira et al. 2016). It’s a win-win for your waistline and your glucose metabolism.

Another way to maintain healthy glucose levels in the blood is to get glucose into muscle via the glucose transporter type 4 (GLUT4). Muscle contraction can activate GLUT4, which allows your muscles to take up glucose directly from the blood without insulin. Glucose removal from the blood, without the use of insulin, is what you want. When glucose goes to the muscle, it is used for energy and not stored as fat (Chen et al. 2017). All exercise increases GLUT4 in muscle cells. However, fasted exercise increases it even more, helping you to better maintain both healthy blood sugar and insulin levels.

Improved Mitochondria Function

Mitochondria are your cell’s energy producers and important signaling organelles. Keep them happy and healthy, and the reward will be more energy, clearer thinking, and enhanced strength and endurance. There are two ways to improve your mitochondria, improve their function, or increase the number of mitochondria. Fasted exercise does both better than fed exercise. Two essential mitochondrial enzymes, citrate synthase and β-hydroxyacyl coenzyme A dehydrogenase are both boosted with fasted exercise, which allows your mitochondria to produce more energy faster (Proeyen et al. 1985).

In addition to improving mitochondria function, another one of the benefits of fasted exercise is an increase in the number of mitochondria you have. Fasted exercise increases the number of mitochondria you have by increasing SIRT1, a protein implicated in healthspan, longevity, and mitochondria biogenesis. Fed exercise does not have this same effect (Aird et al. 2018).

If you want to further optimize your mitochondria, try my Body, Mind, Goal program. It is a 30-Day program complete with meal plans, exercise programs, and stress management techniques to optimize your mitochondria and give you a total systems upgrade in just 30 days.

Improved Lipid Profile

Your blood lipid profile is a measure of the fat and fat-like substances in your blood. It provides insight into your risk of cardiovascular disease. While any exercise can lower your risk of cardiovascular disease, fasted exercise is even more beneficial. Fasted exercise lowers circulating levels of triglycerides and very low-density lipoprotein (VLDL) two significant markers of increased risk of heart disease (Wallis and Gonzalez 2019).

All forms of fasted exercise will give you these benefits. However, there are several differences between a fasted cardio workout and a fasted resistance training workout. Furthermore, before deciding if intermittent fasting and working out is for you, it is crucial to know what your health and fitness goals are.

Benefits of Fasted Cardio

In addition to increasing fat oxidation, improving glucose metabolism, giving your mitochondria a boost, and improving your lipid profile, research shows that combining intermittent fasting and endurance training can improve VO2max (Correia et al. 2020). VO2max is a measure of your body’s ability to consume and use oxygen. A higher VO2max indicates better cardiorespiratory fitness and better endurance capacity. This improvement in VO2max may be a result of the improved body composition seen with intermittent fasting.

While one of the benefits of fasted cardio is an improvement in VO2max and healthier mitochondria, fasting before an endurance competition like a marathon will not help your performance. So train fasted and compete fed for the best results.

Benefits of Fasted Resistance Training

Fasting before a resistance training workout will help you burn more fat as fuel during the workout. Furthermore, even though your stomach may be growling, research shows that a fasted resistance training workout will feel no more challenging than a similar workout in a fed state. Plus, fasting will not affect your performance. You should be able to lift just as much weight fasted as fed (Tinsley et al. 2017).

While there are benefits to fasting before a resistance training workout, to determine if this is the best approach for you, it is essential to decide what your fitness goals are. While research shows that it is possible to make strength gains while exercising fasted, the same research shows that it can be challenging to build muscle while working out fasted.

Can I build muscle while intermittent fasting?

If your goal is to build muscle, intermittent fasting is probably not the way to go. Several studies looking at intermittent fasting and resistance training found no change in muscle size after an 8-week training period. While subjects in these studies did not build muscle while fasting, they did not lose muscle mass either, they simply maintained. These results do not come as a surprise as two of the main hormones involved in muscle growth, testosterone, and IGF-1 both decrease with intermittent fasting (Moro et al. 2016). However, subjects in these studies did see improvements in strength after 8-weeks of intermittent fasting and resistance training. So if your resistance training goal is to get stronger, than intermittent fasting may be the way to go. However, if your resistance training goal is to build muscle, go ahead and eat before your workout.

How To Implement

It can take some time to see intermittent fasting results with exercise. The benefit will not be immediate in everyone. So stick with it. To experience the benefits of fasted exercise, you have to be metabolically flexible. Metabolic flexibility means that your body has to be able to burn whatever fuel source is available to it, either fat or carbohydrates. In the case of fasted exercise, it needs to be able to burn fat as fuel instead of carbohydrates.

So what can you do to become more metabolically flexible? Stress the system. You can stress the system by limiting food intake (fasting), limiting macronutrient intake (limiting carbs), and exercising. Furthermore, research shows that just ten days of exercise can improve metabolic flexibility. So stick with it for a least ten days (Rynders et al. 2018).

Now that you’ve made yourself metabolically flexible, its time to optimize fasted exercise.

How To Optimize Fasted Exercise

Exercise first thing in the morning after an 8 – 12 hour overnight fast. Fasted means nothing but water, black tea, and black coffee for 8 – 12 hours.

To optimize fat burning, perform endurance exercise for 60 – 90 minutes at 50% – 70% intensity.

Do not fast before a big event when performance matters, such as a marathon. One study found that fasting can hinder performance in endurance events over 60 minutes.

Take your workout outside. In addition to all the benefits of fasted exercise, you get the added benefit of working out in nature, which can boost mood.

Try high-intensity interval training to further improve mitochondria function (Ma et al. 2013).

How To Exercise Safely During Intermittent Fasting

Intermittent fasting and working out is generally very safe. However, there are a few additional safety measures to follow to optimize results and minimize the risk of injury.

Start with a shorter fast and easier workout. This plan will give you a chance to see how you feel working out while intermittent fasting and make any necessary adjustments.

Drink plenty of water. You can drink plain or sparkling water during a fast. Make sure you stay hydrated.

Plan your post-workout meal. The type of workout you do will determine what the optimal macros of your post-workout meal. After a resistance training workout, your body will need more protein to build and repair muscle. After a high-intensity interval workout, your body will need carbs to replenish depleted glycogen stores. If you would like a complete breakdown of what to eat after each type of workout, check out Exactly What To Eat To Optimize Your Workout, According to Science.

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