Intermittent fasting doesn’t require you to take it easy all the time. On the contrary, the fasted state improves the health benefits of exercise.
Furthermore, intermittent fasting can even help you build muscle if you use it correctly. You can find out how to combine it correctly in this article.
Intermittent Fasting and Working Out
Intermittent fasting involves eating within a certain period and fasting the rest of the day.
Although there are several forms of intermittent fasting, the most popular is fasting for a 16-hour window.
Therefore, in classic intermittent fasting, you can only eat during a window of 8 hours per day, for example, from 12:00 to 20:00.
Since this method aims to reduce fat while you gain muscle mass, it is also called the Lean Gains method.
Besides 16/8 intermittent fasting, the following intermittent fasting methods exist:
- One-Day Fasting (6:1 Diet) – you do not eat anything on a full day a week
- Two-Day Fasting (5:2 Diet) – you do not eat for two days (often with a small meal)
- Alternate Day Fasting (ADF) – Eat one day, fast one day (often with a small meal)
- One Meal A Day (OMAD) – 23/1 intermittent fasting, where you eat once a day
Whether there are additional benefits to combining Intermittent Fasting and exercise, we now take a closer look based on studies.
Can You Workout While Intermittent Fasting?
A persistent myth about fasting is that you have to take it easy all the time. If you already feel tired, the surest way to eventually feel terrible is to rest even more.
Instead, an activity can help your body kick into gear and get more efficient at burning fat.
For this reason, the question of whether it makes sense to exercise during intermittent fasting can usually only be answered in the affirmative.
Also, fasted exercise amplifies its benefits. If you feel just great while fasting, you must, therefore, by no means lie around like a couch potato.
Working out and intermittent fasting also promote blood sugar regulation and can prevent even rare digestion problems during fasting.
Nevertheless, especially if you are new to Intermittent Fasting, you should start with mild physical activity and always listen to your body.
Can Intermittent Fasting Work Without Exercise?
In principle, intermittent fasting can work without exercise since it sets the hormonal course for weight loss and improved health.
Ultimately, obesity is more a hormonal imbalance than a caloric one, as the world-renowned neuroendocrinologist Dr. Robert Lustig concludes (Lustig 20011).
In this context, the storage hormone insulin in our body represents the crux of the matter. When insulin levels are high, the hormone blocks the enzyme that breaks down body fat (Meijssen et al. 20012).
Moreover, scientists can already predict about 75% of possible gains and losses in overweight people using insulin levels (Kong et al. 20133).
Those unhealthily high insulin levels that plague us today have two primary causes:
- High-carbohydrate diets
- Constant eating
Intermittent fasting addresses the latter problem by restoring a natural balance between eating and fasting.
To finally burn stored body fat as a source of energy, the carbohydrate stores in the liver and muscle mass must first be emptied.
In addition to intermittent fasting, working out also helps to do so. Accordingly, sport increases the energy demand during intermittent fasting, which causes the glycogen stores to deplete even faster.
That is why sport in a fasted state can significantly accelerate fat burning. Those who do not eat for a long time and practice sports on an empty stomach thus increase fat burning effectiveness.
Nevertheless, intermittent fasting can work even without exercise, as long as you do not constantly fill the carbohydrate stores.
Therefore, combining intermittent fasting with a low-carbohydrate diet like the keto diet is beneficial.
Keto, Working Out, and Intermittent Fasting
Fasted exercise is an efficient way to use up muscle glycogen stores, which is key to tapping into body fat as a primary energy source.
This burning fat process is called ketosis, and contrary to many myths, it is an entirely natural mechanism that has ensured our species’ survival.
During food intake, glucose is transported from the bloodstream toward the cells due to the messenger insulin. Then the body stores this glucose as glycogen in liver and muscle cells.
Glycogen is easy to break down and can therefore get quickly into the bloodstream. Thus, the body prefers glycogen stores before tapping energy from fat reserves.
Thus, glycogen stores are the checking account, and fat stores are the body’s savings account. Only when the checking account is empty, it has to draw on the savings.
When food was once scarce in winter, people were forced to fast and live off their fat reserves. This way, ketosis ensured the continued existence of humankind.
Working out and intermittent fasting both use up glycogen in the body, which speeds up the process of switching to burning fat as a primary energy source.
However, if one starts from a ketogenic diet, the body has a distinct starting advantage.
Thanks to empty glycogen stores exercise directly increases fat burning instead of using up glycogen first.
When to Workout When Intermittent Fasting
As we have already concluded, exercise during intermittent fasting makes sense just within the fasting period.
So whether you exercise in the morning or the evening is not significant. What is more important is that you have fasted for a sufficient time. The longer the fasting period before exercise, the greater the effect on fat oxidation.
Therefore, the best time for exercise depends on your intermittent fasting plan. If you skip breakfast due to 16/8, a workout before lunch will have the most excellent effect.
If instead, you fast for 24 hours from dinner to dinner, exercise is best in the evening before the meal.
Benefits of Intermittent Fasting and Working Out
In general, exercise and fasting can help you reach your health goals faster, especially if they involve fat loss. Here are some of the most important benefits of working out in a fasted state.
1. Enhanced Fat Burning
Combining working out and intermittent fasting is especially smart if you want to improve your body composition.
When carbohydrate stores are empty due to fasting, the body sustainably taps into fat tissue as the next available energy source (Achten et al. 20044).
In contrast, eating carbohydrates before working out inhibits potential fat burning (Horowitz et al. 19975).
Therefore, the combination with a low-carbohydrate or ketogenic diet is even more efficient, because in this case, the glycogen stores are already empty. Thus, the body can immediately start fat oxidation.
Along these lines, studies on fasted exercise show that not only do you burn more fat this way, but the amount of fat released per cell also increases (Hansen et al. 20176).
Moreover, further studies suggest that more blood is flowing to the abdominal area when fasted, helping burn fat cells stored in this area (Gjedsted et al. 20077).
2. Increased Autophagy
Besides fat burning, autophagy is the main benefit of fasting.
This process is a natural recycling mechanism in your body that replaces broken proteins in cells with new ones and drains toxins from your body.
That’s why autophagy is mainly known to prevent diseases like Alzheimer’s, type 2 diabetes, and cancer. Furthermore, it can slow down the aging process (Gelino et al. 20128).
With this in mind, fasting is one of the best ways to activate autophagy (Bagherniya et al. 20189).
When you don’t eat for about 14 hours, the intercellular recycling system kicks into high gear (Yang et al. 201710).
In addition to fasting, regular and intense exercise can also really kick-start the process.
Accordingly, one study discovered increased autophagy markers in people who played soccer all their lives. In a direct comparison, people of the same age who had not exercised their entire lives performed significantly worse (Mancini et al. 201911).
Also, scientists could detect autophagy activity in the liver, muscle, pancreas, and adipose tissue in mice that regularly exercised on a treadmill (He et al. 201212).
Moreover, according to a recent study, exercise intensity is more crucial for autophagy in muscle cells than the fasting state itself (Schwalm et al. 201513).
Hence, High-Intensity Interval Training (HIIT) is an excellent way to achieve autophagy incredibly quickly in combination with fasting.
3. Improved Muscle Gains
Fasting is one of the most effective ways to stimulate human growth hormone (Ho et al. 198814).
Therefore, intermittent fasting increases the human growth hormone (HGH), promoting bone, cartilage, and muscle development. As a result, you get bigger, stronger muscles and protection against age-related bone and muscle loss.
By fasting, you maximize the release of growth hormone until you break the fasting window after exercising with a meal. This way, you send the body into an anabolic state at the right time for targeted muscle building.
Since the production of growth hormone decreases after 30, you can use intermittent fasting to help your body continue to produce this vital neurotransmitter.
Accordingly, HGH helps with muscle recovery after exercise and sets the stage for healthy bones, organs, and longevity (Besson et al. 200315).
But again, it is low insulin levels that enable growth hormone release. Regular intermittents of fasting, such as the 16/8 method, create the foundation for this.
4. Enhanced Endurance
When you practice cardio exercise, your endurance is only as good as your body’s ability to deliver necessary oxygen to the right cells.
Endurance training can help increase this process of oxygen delivery. The measure of this is the maximal oxygen uptake, often referred to as VO2-Max.
VO2-Max measures the maximum amount of oxygen your body uses per minute during an endurance workout when you’re pushing yourself hard.
Increasing this value allows your body to take in more oxygen and deliver it to your muscles. This way, you can improve your performance during cardio workouts.
One study compared the VO2-Max values of people in a fasted and fed state. The group that had cereal for breakfast performed significantly worse than those who ate nothing after getting up.
At the start of the study, all participants had average VO2-Max values of about 3.5 liters per minute (L/min). After ergometer training, VO2 max increased by about 10 percent in the fasted group.
In contrast, the fed group saw only a 2.5 percent improvement in VO2 max (Stannard et al. 201016).
In short, intermittent fasting allows people to increase their maximal oxygen uptake through exercise significantly better than those who eat breakfast or eat before a workout.
5. Fewer Digestion Issues
Have you ever experienced indigestion or nausea after eating a pre-workout protein bar or shake?
If so, you’re not alone in this. These pre-workouts have become mainstream in the fitness and food industries because there’s good money to make with them.
However, as we learned before, pre-workout food hinders performance enhancement rather than the other way round. Moreover, in particular, bars and shakes are full of carbohydrates and proteins that increase insulin secretion.
For this reason, they ultimately prevent fat burning as well.
Therefore, exercising during intermittent fasting helps you avoid digestive discomfort and ensures that you get to your goals faster.
How to Work Out and Do Intermittent Fasting
Combining working out and intermittent fasting can generate sensational results. But if you want to succeed, there are three basic rules to follow.
1. Listen to Your Body
Common sense is always needed when doing sports. With this in mind, you should regulate your training intensity based on your overall feeling, especially if you have just started intermittent fasting.
If you don’t feel well, refrain from the training session and take a day off.
Unless you’re just feeling sluggish, grab a bike or go for a walk. If you feel entirely fit while fasting, don’t hesitate to hit the gym.
For example, push-ups help me right after I get up to generate extra energy and a sense of well-being for the whole day.
You can start with ten repetitions a day and slowly work your way up to three times ten. With the necessary continuity, you can reach 50 or even 100 repetitions.
2. Do Not Eat Before Working Out
Authors often overlook this vital point, mostly when they are selling sports nutrition.
If you drink an energy drink or eat protein bars before exercise, the carbohydrates in them will inhibit fat burning (Horowitz et al. 199717).
Since the increased insulin level blocks the enzyme responsible for fat breakdown, this is hardly surprising (Meijssen et al. 200118).
Moreover, the body then preferentially consumes the energy supplied by food in the bloodstream.
The need to supply the body with external energy before training is a widespread misconception drilled into us by advertising campaigns for decades.
In the end, it would be far more effective to burn stored body fat instead.
Therefore, there are only two real reasons to eat before exercise:
- You want to build body fat in addition to muscle mass.
- You are a professional athlete and train three times a day.
For this reason, the ubiquitous orientation from hobby sports to competitive sports has prevented countless people from getting into the shape they crave.
3. Stay Hydrated
Whether in a fasted state or not, you need to be adequately hydrated to get a top-notch workout.
When we fast, we do not absorb the fluids we usually get from foods. Therefore, it is crucial to ensure adequate hydration before and after exercise.
Drinking water just before training is not enough. After all, it takes a while for the water to get from the stomach to the muscles.
For this reason, it makes sense to drink enough water at least 30 minutes before training and not just immediately before.
If you drink sufficient fluids before and after your workout, you should not feel any cravings afterward. These cravings usually occur because we are dehydrated.
For example, this way, you’ll find it easier to work out in the morning and not break your fast until noon.
Why You Should Be Working Out on Intermittent Fasting
For many people, the increased release of adrenaline during intermittent fasting helps them work out more consistently.
Besides, the combination of working out and intermittent fasting helps to reduce stress and cope with anxiety.
In my experience, fasting also makes you go into workouts with more vigor and helps you concentrate better.
With this in mind, ketones can cross the blood-brain barrier during fasting and deliver clean energy to the brain sustainably (Hallböök et al. 201419).
The bottom line is that a low carb diet like the keto diet best supports intermittent fasting’s health benefits.
Intermittent Fasting and Working Out FAQ
Can I combine intermittent fasting and bodybuilding?
Bodybuilders have been using classic 16/8 intermittent fasting for decades to reduce fat mass while gaining lean mass.
Does intermittent fasting cause muscle loss?
Contrary to popular belief, intermittent fasting increases the release of growth hormones, which protect muscle mass during fasting and help build muscle.
Does intermittent fasting work without exercise?
Of course, intermittent fasting can work without exercise. But working out helps to reduce the carbohydrate stores and thus to get into fat-burning faster.
Can intermittent fasting be combined with HIIT training?
Healthy people can combine intermittent fasting with HIIT training. According to recent studies, HIIT training is particularly good at enhancing the health benefits of intermittent fasting.
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