Intermittent fasting has become one of the most popular nutritional strategies for losing weight, increasing energy, enhancing mental clarity, improving digestive symptoms, and just general health and wellness. While the science supporting these benefits accumulates, there are still many unanswered questions about intermittent fasting. The most common questions we hear are about exercise during intermittent fasting. In this article, we’ll share our opinion on the available science about exercise and intermittent fasting to help you decide if this combo is right for you.
We won’t go into the basics of fasting and intermittent fasting. You can find it in some of our more in-depth articles on the subject. What you need to know is that intermittent fasting consists of manipulating fasting and nutrition to help achieve various health outcomes. Compared to extended fasting, intermittent fasting has a much shorter fasting period. The fasting period for intermittent fasting is usually 16-20 hours with an eating window of 4-8 hours. This approach has been shown to provide many health and even athletic performance-related benefits.
The short answer here is yes. Many people report a lot of benefits from exercising while in a fasting state. Over the past couple of years, I’ve started incorporating intermittent fasting and working out myself and have found that it helps improve my energy levels during exercise, leads to better fat loss results, and even provides a boost, mood and mental clarity making both for a better workout.
The real question you might ask is:
Are intermittent fasting and working together safe?
The short answer here is also yes but it comes with “it depends”. If you don’t exercise or eat well, transitioning to quick workouts can definitely pose some challenges. If your body is not used to generating energy during fasting or feeding the demands of an exercising body, you may experience low blood sugar levels resulting in fatigue, shivering and hypoglycemia which can lead to fainting during exercise.
This does not mean intimidating you with intermittent fasting and exercise. The two are actually a great pair! We just suggest that you get into the habit of exercising and fasting separately before combining the two.
One reason for intermittent fasting and working so well together is that they both produce similar responses from the body, especially glycogen depletion. Glycogen is the body’s stored form of glucose or carbohydrates. When we don’t eat and when we exercise, we call up our glycogen stores for fuel reserves to provide us with the energy we need to function. Once we burn off these carbohydrate stores, our body begins to burn fat to provide energy to continue to maintain proper function. If you continue to fast or exercise, the body will start converting some of this fat into an additional source of energy known as ketone bodies. If you don’t know what ketones are, check out this article.
Because of the similarities in our bodies’ response to fasting and exercise, these two strategies pair well to produce powerful metabolic improvements that can lead to a range of health benefits. Let’s dive into the benefits of this combo.
Benefits of exercising while fasting
Now that we know we can exercise in a fasting state, the big question is why would you do it? Here’s why you should combine exercise and intermittent fasting:
Burning Fat: We begin to deplete glycogen levels when we fast, which means that when we practice fasting, we are actually closer to utilizing fat as an energy source which is why research shows that exercising in a fasting state can increase fat oxidation [*] Which makes it a great weight loss strategy.
Benefit #1: Increased Ketone Production:
Since ketones are made up of fat, we can expect intermittent fasting and exercise to lead to higher ketone levels. This is a great strategy for those looking to reap the energy and mental clarity benefits of ketosis.
Benefit #2: Autophagy
Autophagy is a natural process of breaking down damaged and unnecessary cells. This bodily function exists to prevent cells we don’t want to copy from multiplying, such as cancer cells. Fasting has been shown to enhance autophagy, and although there have been no studies looking at fasting and the action of autophagy, we hypothesize that a deeper degree of ketosis and lower blood sugar levels would lead to more autophagy.
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Benefit #3: Gain muscle
This is tough Fasting alone will not lead to muscle gain, and if you are fast but have a poor exercise regimen and poor post-workout nutrition, you are less likely to build muscle. However, fasting has been shown to stimulate human growth hormone (HGH).[*] (which has a wide range of benefits outside of muscle growth) Then a combination of fasting, resistance training and adequate protein/calorie intake during the feeding period can lead to an increase in muscle mass.
Benefit #4: Endurance Performance
Research has found that exercising in a fasting state can lead to better VOx-max performance or, in other words, better endurance performance. [*].
Benefit #5: Less Bloating
Another great benefit of combining fasting with exercise is the digestive benefits. When you’re fasting, you’re also giving your digestive system a rest which can mean you go into your workout feeling less bloated and lighter on your feet.
You may already have this question running through your head. Can you combine keto, fasting, and exercise? The answer is yes. In fact, this might be the best time to do so.
Keto and fasting are another great combination of healthy strategies, and for the same reasons why fasting and exercise do: they produce similar results. Fasting and exercise can put us in a fat-burning state, but if you break your fast by eating carbs, you will stop burning fat. Keto is a way to keep us burning fat, so if your goal is to burn fat all day long, the keto diet plus fasting and exercise may be a great option for you!
Note: Quick workouts are also a lot easier on keto because your body is already adapting to fat which means it is effective in burning fat and producing ketones.
How to combine intermittent fasting and exercise
The first step to combining intermittent fasting with exercise is to determine if it’s right for you. Remember that like any health strategy, this combo is a tool that must be used with intent and purpose and must provide benefit to your life, not make it worse.
Do I have to exercise while fasting?
The benefits of exercising while fasting won’t outweigh the downsides of hating it or not being able to perform well when exercising. I exercise while fasting because I feel and perform better when I do. Try it several times. If you find that you are low on energy, very hungry, or your exercise performance struggles with training on an empty stomach, this method may not be for you. So we get a fleshy adaptation of this.
What is the best type of fasting?
Fasting can be combined with any type of exercise, from cardio to strength training. For beginners, low-intensity exercises like basic cardio are a great place to start because it’s best to make this easier. Make sure to allow your body to adjust and increase its intensity as tolerated. Fast cardio, especially high-intensity interval training (HIIT), is also a great option if your goal is to burn fat.
Once you get more experience with intermittent fasting and exercise, try more intense forms of exercise like resistance training or cardio.
What is the best time for intermittent fasting and exercise?
Intermittent fasting can be combined with exercise at any time during the fasting window. Since this is a very powerful combination, I like to use this strategy whenever my goal is to increase fat burning or increase ketone production to improve brain function.
How can I improve intermittent fasting and exercise?
The best way to improve is to adapt to the ketogenic diet. Keto pairs well with fasting and exercise not only because of the greater benefits, but also because the keto diet makes it easier to work out in a fasting state.
For those who experience high rates of sweating during workouts, pre-workout and post-workout electrolytes may also be a great way to help you improve this combo. There is controversy over whether consuming electrolytes keeps you in a fasting state but since they do not spike blood sugar or insulin, our position is that they can be an effective vital tablet for fasting exercise.
While fasting and exercise don’t have to go together, they make a powerful combination that can help us lose weight and make significant improvements in metabolic health. Intermittent fasting and exercise are a lot easier if you’re already on a keto diet, so for keto dieters looking to ramp up fat burning, boost ketone production, or attack other fitness goals, it might be time to give this combo a shot. Try.