Intermittent fasting has become one of the most popular dietary strategies for weight loss, increasing energy, promoting mental clarity, improving digestive symptoms, and just overall health and wellness. While the science supporting these benefits is stacking up, there are still a lot of unanswered questions circling around about intermittent fasting. The most common questions we hear are about working out while intermittent fasting. In this article, we are going to share our take on the available science around working out and intermittent fasting to help you determine if this combo is right for you.
We are not going to go too deep on the basics of fasting and intermittent fasting. You can find those in some of our more in-depth pieces on the topic. What you do need to know is that intermittent fasting consists of manipulating your fasting and feeding window to help produce various health results. Compared to extended fasting, intermittent fasting has a much shorter fasting period. Typically a fasting window for intermittent fasting is 16-20 hours with an eating window of 4-8 hours. This approach has been shown to provide numerous health benefits and even benefits related to athletic performance.
The short answer here is yes. Many people are reporting a lot of benefits from exercising in a fasted state. Over the last couple of years I have started to incorporate intermittent fasting and working out myself and have found that it helps improve my energy levels during my workout, produces better fat loss results, and even provides a boost and mood and mental clarity which both make for a better workout.
The real question you may be asking is:
Is intermittent fasting and working out together safe?
The short answer here is also yes but it does come with an “it depends” depends. If you have not been exercising or eating well, the jump to fasted workouts could definitely pose some challenges. If your body is not accustomed to creating energy while fasted or fueling the demands of an exercising body, you could experience low blood sugar levels resulting in fatigue, shakiness, and hypoglycemia which could lead to passing out while exercising.
This is not meant to scare you away from intermittent fasting and working out. The two are actually a great pair! We just suggest that you accustom yourself to both exercise and fasting separately before combining the two.
One of the reasons why intermittent fasting and working out pair so well together is because they both produce similar responses from the body, mainly glycogen depletion. Glycogen is our body’s stored form of glucose or carbohydrate. When we aren’t eating and when we exercise, we call on glycogen stores for a fuel reserve to provide us with the energy we need to function. Once we have burned through these carbohydrate stores, our body begins to burn fat to supply energy to continue to maintain proper function. If fasting or exercise continues, the body will even start converting some of that fat into an additional energy source known as ketone bodies. In case you don’t know what ketones are, check out this article.
Due to the similarities in our body’s response to fasting and working out, these two strategies pair well to produce robust metabolic improvements that can lead to an array of health benefits. Let’s dive into the benefits of this combo.
Benefits of working out while fasted
Now that we know that we can work out in a fasted state, the big question is why would you? Here’s why you should consider combining working out with intermittent fasting:
Fat burning: We start depleting glycogen levels when we fast, which means when we exercise fasted we are already closer to or already to tapping into fat as an energy source which is why research shows exercising in a fasted state can increase fat oxidation [*] making it a great weight loss strategy.
Benefit #1: Increased ketone production:
Since ketones are created from 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 the natural process of breaking down damaged and unneeded cells. This bodily function exists to prevent cells that we don’t want replicating from replicating, like cancer cells. Fasting has been shown to promote autophagy and while there have not been any studies looking at fasting and working out on autophagy, we assume that the deeper degree of ketosis and lower blood sugar levels would be conducive to more autophagy.
Benefit #3: Muscle gain
This is a tough one. Fasting alone will not lead to muscle gain and if you fast but have a poor workout regime and poor post-workout nutrition, you are not likely to build muscle. However, since fasting has been shown to stimulate human growth hormone (HGH)[*] (which has a wide array of benefits outside of muscle growth) then combining fasting with resistance training and adequate protein/calorie intake during the feeding window could lead to increases in muscle mass.
Benefit #4: Endurance performance
Research has found that exercising in a fasted state can lead to better VOx-max performance or in other words, better endurance performance [*].
Benefit #5: Less bloating
Another great perk of combining fasting and working out is the digestive benefits. When you are fasting, you are also giving your digestive system a rest which can mean entering your workout feeling less bloated and lighter on your feet.
You may have already had this question circling in your head. Can you combine keto, fasting, and working out? The answer is yes. In fact, this may be the best time to do it.
Keto and fasting is another great health strategy combo and for similar reasons why fasting and working out are: they produce similar outcomes. Fasting and exercise can put us in a state of fat burning but if you break the fast by loading up on carbs, you’ll be turning that fat burning off. Keto is a way to keep us in the fat burning state so if your goal is all day fat burning, the keto diet plus fasting and exercise may be a great option for you!
Note: Fasted workouts are also a lot easier on keto because your body is already fat-adapted meaning that it is efficient at burning fat and producing ketones.
How to combine intermittent fasting and working out
The first step to combining intermittent fasting and working out is deciding if it’s right for you. Remember that like any health strategy, this is combo is a tool that should be used with intent and purpose and it should provide benefit to your life, not make it worse.
Do I have to work out while fasting?
The benefits of exercising in a fasted state will not outweigh the cons of you hating it or not being able to perform well when exercising. I exercise fasted because I feel and perform better when I do it. Give it a try a few times. If you find that you are low energy, extremely hungry, or your exercise performance is suffering from working out on an empty stomach, this approach may not be for you. Until we get you fat-adapted that is.
What is the best type of fasted exercise?
Fasting can be combined with any type of exercise from cardio to strength training. For beginners, low-intensity exercise like basic cardio is a great place to start since this is something that is best eased into. Make sure you let your body get adjusted and increase intensity as tolerated. Fasted cardio, especially high-intensity interval training (HIIT) fasted cardio, is also a great option if your goal is fat burning.
Once you have a little more experience with intermittent fasting and working out, then try more intense forms of exercise like resistance training or cardio sports.
When is the best time to intermittent fast and work out?
Intermittent fasting and exercise can be combined anytime during your fasting window. Since this is a pretty powerful combo, I like to use this strategy whenever my goal is to ramp up fat burning or increase ketone production for better brain function.
How do I optimize intermittent fasting and working out?
The best way to optimize is by getting keto-adapted. Keto pairs well with fasting and working out not just because of the greater benefits, but also because keto makes it easier to work out in a fasted state.
For those with high sweat rates during workouts, electrolytes pre-workout and post-workout may also be a great way to help you optimize this combo. There is debate on whether consuming electrolytes keeps you in a fasted state but since they don’t spike blood sugar or insulin, our stance is that they can be an effective biohack for your fasted workout.
While fasting and working out do not have to go together, they do make a powerful combo that can help us lose weight and make significant metabolic health improvements. Intermittent fasting and working out is a lot easier if you are already keto-adapted so for you keto dieters looking to ramp up your fat-burning, boost your ketone production, or attack other fitness goals, it may be time to give this combo a try.