Intermittent Fasting | Working Out | When | Benefits | Tips | FAQ
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 help you build muscle if you use it correctly. You can find out how to combine it correctly in this article.
What Is Intermittent Fasting 16/8?
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 8 hours daily, 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 schedules 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.
Should You Combine Intermittent Fasting and Working Out?
A persistent myth about fasting is that you must always take it easy. 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, whether it makes sense to exercise during intermittent fasting can usually only be answered in the affirmative.
Also, fasted exercise amplifies its benefits. You must not lie around like a couch potato if you feel great while fasting.
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.
Does 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 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 sports in a fasted state can significantly accelerate fat-burning. Those who do not eat for longer before exercising increase fat-burning effectiveness.
Nevertheless, intermittent fasting can work even without exercise if you do not constantly fill the carbohydrate stores.
Therefore, combining intermittent fasting with a low-carbohydrate diet like the keto diet is beneficial.
How Can I Burn the Most Fat During Fasting?
Fasted exercise efficiently uses up muscle glycogen, which is crucial to tap 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.
Food intake transports glucose from the bloodstream toward the cells due to the messenger insulin. Then the body stores this glucose as glycogen in the liver and muscle cells.
Glycogen is easy to break down and can get quickly into the bloodstream. Thus, the body prefers glycogen stores before tapping energy from fat reserves.
Thus, glycogen stores are like a checking account, and fat stores are the body’s savings account. When the checking account is empty, it must draw on the savings.
When food was scarce in winter, people were forced to fast and live off their fat reserves. This way, ketosis ensures the continued existence of humankind.
Working out and intermittent fasting both use glycogen, which speeds up switching to burning fat as a primary energy source.
However, the body has a distinct starting advantage if one starts from a ketogenic diet.
Exempting glycogen stores directly increases fat-burning instead of using up glycogen first.
When Should I Workout With Intermittent Fasting?
As we have already concluded, exercise during intermittent fasting makes sense 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 Working Out on Intermittent Fasting
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 you burn more fat this way, increasing the amount of fat released per cell (Hansen et al. 20176).
Moreover, further studies suggest that more blood flows 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 aging (Gelino et al. 20128).
With this in mind, fasting is one of the best ways to activate autophagy (Bagherniya et al. 20189).
The intercellular recycling system kicks into high gear when you don’t eat for about 14 hours (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 mice regularly exercising on a treadmill in the liver, muscle, pancreas, and adipose tissue (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 more substantial 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 gain.
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 muscles recover 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 suitable 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, the fasted group’s VO2 max increased by about 10 percent.
In contrast, the fed group saw only a 2.5 percent improvement in VO2 max (Stannard et al. 201016).
In short, intermittent fasting increases maximal oxygen uptake through exercise significantly better than those who eat breakfast or 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 they have good money to make.
However, as we learned before, pre-workout food hinders performance enhancement rather than the other way around. Moreover, 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 you reach your goals faster.
How to Combine Intermittent Fasting and Working Out
Combining working out and intermittent fasting can generate sensational results. But if you want to succeed, there are three basic rules.
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.
If you’re feeling sluggish, grab a bike or walk. Don’t hesitate to hit the gym if you feel fit while fasting.
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 daily and slowly work 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 selling sports nutrition.
If you drink an energy drink or eat protein bars before exercise, carbohydrates 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 preferentially consumes the energy food supplies 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, you must be adequately hydrated to get a top-notch workout.
We do not absorb the fluids we usually get from foods when we fast. 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 immediately before.
You should not feel cravings afterward if you drink sufficient fluids before and after your workout. 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.
Working Out on Intermittent Fasting Boosts Weight Loss
The increased release of adrenaline during intermittent fasting helps many people 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 sustainably deliver clean energy to the brain (Hallböök et al. 201419).
Working out in a fasted state lets your body tap into stored fat for energy and ultimately lose weight faster.
The bottom line is that a low-carb diet like keto best supports intermittent fasting’s fat-burning capability.
Intermittent Fasting and Working Out FAQ
What happens if you workout while fasting?
Working out during fasting helps you burn fat more efficiently.
Do you lose weight faster if you exercise while fasting?
While fasting, insulin levels are low, enhancing exercise’s weight loss effect.
Is intermittent fasting good if you workout in the morning?
If you skip breakfast due to intermittent fasting working out in the morning will maximize fat loss and muscle gain.
What is the best exercise during intermittent fasting?
It is best to do strength training during intermittent fasting due to enhanced growth hormone release.
1 Lustig RH. The neuroendocrinology of childhood obesity. Pediatr Clin North Am. 2001 Aug;48(4):909-30. doi: 10.1016/s0031-3955(05)70348-5. Review. PubMed PMID: 11494643.
2 Meijssen S, Cabezas MC, Ballieux CG, Derksen RJ, Bilecen S, Erkelens DW. Insulin mediated inhibition of hormone sensitive lipase activity in vivo in relation to endogenous catecholamines in healthy subjects. J Clin Endocrinol Metab. 2001 Sep;86(9):4193-7. doi: 10.1210/jcem.86.9.7794. PubMed PMID: 11549649.
3 Kong LC, Wuillemin PH, Bastard JP, Sokolovska N, Gougis S, Fellahi S, Darakhshan F, Bonnefont-Rousselot D, Bittar R, Doré J, Zucker JD, Clément K, Rizkalla S. Insulin resistance and inflammation predict kinetic body weight changes in response to dietary weight loss and maintenance in overweight and obese subjects by using a Bayesian network approach. Am J Clin Nutr. 2013 Dec;98(6):1385-94. doi: 10.3945/ajcn.113.058099. Epub 2013 Oct 30. PubMed PMID: 24172304.
4 Achten J, Jeukendrup AE. Optimizing fat oxidation through exercise and diet. Nutrition. 2004 Jul-Aug;20(7-8):716-27. doi: 10.1016/j.nut.2004.04.005. Review. PubMed PMID: 15212756.
5 Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise. Am J Physiol. 1997 Oct;273(4):E768-75. doi: 10.1152/ajpendo.1997.273.4.E768. PubMed PMID: 9357807.
6 Hansen D, De Strijcker D, Calders P. Impact of Endurance Exercise Training in the Fasted State on Muscle Biochemistry and Metabolism in Healthy Subjects: Can These Effects be of Particular Clinical Benefit to Type 2 Diabetes Mellitus and Insulin-Resistant Patients?. Sports Med. 2017 Mar;47(3):415-428. doi: 10.1007/s40279-016-0594-x. Review. PubMed PMID: 27459862.
7 Gjedsted J, Gormsen LC, Nielsen S, Schmitz O, Djurhuus CB, Keiding S, Ørskov H, Tønnesen E, Møller N. Effects of a 3-day fast on regional lipid and glucose metabolism in human skeletal muscle and adipose tissue. Acta Physiol (Oxf). 2007 Nov;191(3):205-16. doi: 10.1111/j.1748-1716.2007.01740.x. Epub 2007 Sep 3. PubMed PMID: 17784905.
8 Gelino S, Hansen M. Autophagy – An Emerging Anti-Aging Mechanism. J Clin Exp Pathol. 2012 Jul 12;Suppl 4. doi: 10.4172/2161-0681.s4-006. PubMed PMID: 23750326; PubMed Central PMCID: PMC3674854.
9 Bagherniya M, Butler AE, Barreto GE, Sahebkar A. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Res Rev. 2018 Nov;47:183-197. doi: 10.1016/j.arr.2018.08.004. Epub 2018 Aug 30. Review. PubMed PMID: 30172870.
10 Yang JS, Lu CC, Kuo SC, Hsu YM, Tsai SC, Chen SY, Chen YT, Lin YJ, Huang YC, Chen CJ, Lin WD, Liao WL, Lin WY, Liu YH, Sheu JC, Tsai FJ. Autophagy and its link to type II diabetes mellitus. Biomedicine (Taipei). 2017 Jun;7(2):8. doi: 10.1051/bmdcn/2017070201. Epub 2017 Jun 14. PubMed PMID: 28612706; PubMed Central PMCID: PMC5479440.
11 Mancini A, Vitucci D, Randers MB, Schmidt JF, Hagman M, Andersen TR, Imperlini E, Mandola A, Orrù S, Krustrup P, Buono P. Lifelong Football Training: Effects on Autophagy and Healthy Longevity Promotion. Front Physiol. 2019;10:132. doi: 10.3389/fphys.2019.00132. eCollection 2019. PubMed PMID: 30837897; PubMed Central PMCID: PMC6390296.
12 He C, Sumpter R Jr, Levine B. Exercise induces autophagy in peripheral tissues and in the brain. Autophagy. 2012 Oct;8(10):1548-51. doi: 10.4161/auto.21327. Epub 2012 Aug 15. PubMed PMID: 22892563; PubMed Central PMCID: PMC3463459.
13 Schwalm C, Jamart C, Benoit N, Naslain D, Prémont C, Prévet J, Van Thienen R, Deldicque L, Francaux M. Activation of autophagy in human skeletal muscle is dependent on exercise intensity and AMPK activation. FASEB J. 2015 Aug;29(8):3515-26. doi: 10.1096/fj.14-267187. Epub 2015 May 8. PubMed PMID: 25957282.
14 Ho KY, Veldhuis JD, Johnson ML, Furlanetto R, Evans WS, Alberti KG, Thorner MO. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. J Clin Invest. 1988 Apr;81(4):968-75. doi: 10.1172/JCI113450. PubMed PMID: 3127426; PubMed Central PMCID: PMC329619.
15 Besson A, Salemi S, Gallati S, Jenal A, Horn R, Mullis PS, Mullis PE. Reduced longevity in untreated patients with isolated growth hormone deficiency. J Clin Endocrinol Metab. 2003 Aug;88(8):3664-7. doi: 10.1210/jc.2002-021938. PubMed PMID: 12915652.
16 Stannard SR, Buckley AJ, Edge JA, Thompson MW. Adaptations to skeletal muscle with endurance exercise training in the acutely fed versus overnight-fasted state. J Sci Med Sport. 2010 Jul;13(4):465-9. doi: 10.1016/j.jsams.2010.03.002. Epub 2010 May 7. PubMed PMID: 20452283.
17 Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise. Am J Physiol. 1997 Oct;273(4):E768-75. doi: 10.1152/ajpendo.1997.273.4.E768. PubMed PMID: 9357807.
18 Meijssen S, Cabezas MC, Ballieux CG, Derksen RJ, Bilecen S, Erkelens DW. Insulin mediated inhibition of hormone sensitive lipase activity in vivo in relation to endogenous catecholamines in healthy subjects. J Clin Endocrinol Metab. 2001 Sep;86(9):4193-7. doi: 10.1210/jcem.86.9.7794. PubMed PMID: 11549649.
19 Hallböök T, Ji S, Maudsley S, Martin B. The effects of the ketogenic diet on behavior and cognition. Epilepsy Res. 2012 Jul;100(3):304-9. doi: 10.1016/j.eplepsyres.2011.04.017. Epub 2011 Aug 27. Review. PubMed PMID: 21872440; PubMed Central PMCID: PMC4112040.