Intermittent fasting and exercise are essential in cultivating longevity, but should they be combined?
Here we’ll go over all of the questions about exercising while fasting, including the benefits of fasted exercise, as well as some simple tips on how to get the most out of a fasted workout.
What Is Intermittent Fasting?
Simply put, intermittent fasting (IF) is when you only eat at certain times of the day or week. You can choose from different types from fasting for a set number of hours per day or eating only one meal a couple of days per week. The type of fast can be applied depending on your preference and can help your body burn fat.
Types of Intermittent Fasting Diet
You will not eat anything for 16 hours and then have an 8-hour window to ingest food during 16/8 fasting. You can take non-calorie beverages such as black coffee, black tea, and water during your fasting window.
While the 16/8 approach is common for a lot of fasting enthusiasts, you may need to pace your fasting hours and then work your way up to fasting for 16 hours straight. Furthermore, consuming too many snacks or junk food during your 8-hour window might nullify the benefits of 16/8 intermittent fasting.
To optimize the potential health advantages of any fast, consume a balanced meal rich in fruits and vegetables.
The 5:2 diet is a form of fasting in which you typically eat for five days and fasts for two days. It also allows you to choose which days you fast, and there are no limits about what or when you eat on full-calorie days.
Even if it’s only for two days a week, limiting oneself to 500 calories per day is difficult. Furthermore, eating too few calories may cause you to feel uncomfortable or faint. The 5:2 diet can be beneficial but only suitable for some.
A nocturnal fast entails going without eating for an extended period, from the evening through the following morning. According to a 2016 study, a 13-hour overnight fast may lessen the incidence of breast cancer in women1.
One Meal A Day (OMAD)
OMAD fasting requires eating only one meal daily and fasting the rest of the time. The possible health advantages of OMAD are primarily associated with fasting (restricting calorie intake for a specific period) and calorie restriction in general.
People will not eat during this fast for the first 8 hours of their waking day. The person can then eat after the ninth hour.
As the name implies, alternate-day fasting is when a person usually eats one day and fasts the next. You fast every other day on this regimen but can eat whatever you want on the non-fasting days.
Some variations of this diet advocate a “modified” fasting technique that entails ingesting 500 calories on fasting days. Other variants, on the other hand, exclude calories entirely on fasting days.
The Warrior Diet is an intermittent fasting strategy based on ancient warriors’ feeding habits. It entails eating relatively little throughout the day and then eating as much as you want during a 4-hour window at night.
During the 20-hour fast, you are encouraged to consume tiny amounts of dairy products, hard-boiled eggs, raw fruits and vegetables, and non-calorie drinks.
Eat Stop Eat
This intermittent fasting method entails choosing one or two non-consecutive days every week to go without eating or fasting for 24 hours. You can eat anything you like the rest of the week, but it’s still best to eat a well-balanced diet and avoid overindulging.
The logic behind a weekly 24-hour fast is that eating fewer calories will result in weight loss.
However, avoiding meals for 24 hours at a time takes a lot of effort and might lead to bingeing and overeating later on after your fast.
It may also result in disordered eating habits. Before attempting Eat Stop Eat or any fast for that matter, please consult with your doctor to see whether it is a viable weight loss option.
Intermittent Fasting And Exercise: Can You Work Out While Intermittent Fasting?
The quick answer is yes. The longer answer is that it is relative as it is essential to listen to your body.
As with most things, finding a schedule that works for you is vital. The numerous types of IF means you can choose which one based on your lifestyle.
Also, depending on the type of workout you prefer and the time of day you want to exercise, you might need to change your fast to acquire the nutrients your body requires. Picking the right type of fast and workout are especially crucial since it has several advantages but also some its disadvantages.
Benefits Of Fasting And Working Out
The health benefits of working out on an empty stomach are a topic of heated discussion in the fitness nutrition industry, and the jury is still out. The notion goes that by working out in a fasting condition and denying your body a fresh supply of glycogen stores, your body will resort to fat-burning energy.
This should result in increased weight loss and a long-term performance boost through training adaptations. However, there is evidence that this equation is more complex than it appears.
Keeping all sides of the debate in mind, here’s what you need to know about training on an empty stomach:
1. Weight Loss
Exercising in a fasted condition (after fasting for 8 to 12 hours) might increase fat oxidation (or burn) during your workout resulting in weight loss. But how exactly does this work?
Your body stores fat in two places: adipose tissue and triglycerides in muscle fibers. Your body metabolizes lipids and carbohydrates when you exercise, turning them into fuel.
Your body more easily taps carbohydrate storage since they are efficiently mobilized and provide fast energy. However, as those reserves deplete, the pace at which your body burns (or oxidizes) fat increases.
To support this benefit, one study discovered that exercising while fasting resulted in greater weight loss than exercising after a meal2.
According to a review of research on exercise and fasting, it may boost autophagy. Autophagy is a process that aids in destroying undesired or damaged cells to regenerate newer and healthier ones3.
Autophagy is your body’s natural cleaning out process which begins when your cells are stressed or deprived of nutrients. Allowing your body to break down and reuse old cell parts so your cells can operate more efficiently.
According to a 2018 study, IF and exercise may reduce aging and disease processes. This is because IF and exercise can alter metabolism4.
By enhancing metabolism, it makes your body more efficient at breaking down nutrients and burning calories. It also slows down the degradation of DNA, which is what occurs when you age, and accelerates DNA repair, thus slowing down the aging process5.
What Are The Best Exercises During Intermittent Fasting?
Your exercise may be dependent on the type of intermittent fasting you select. If you follow a 16:8 diet, you may exercise both strength and cardio.
However, choose a less strenuous exercise or skip it if you wish to try an alternate day or 24-hour fasting and then continue training on your non-fasting days. Yoga and pilates are good options. Walking is also acceptable.
How to Work Out When You’re Intermittent Fasting
The significant difficulty with intermittent fasting and exercise is that your body requires nourishment to move, function, and grow. That fuel is energy, which comes from food, most notably carbohydrates which is one of the three essential macronutrients that comprise everything you consume.
However, you essentially eliminate that fuel source by reducing your meal consumption through intermittent fasting. This means you may need more energy when it comes time for your next workout session. Here are some guidelines to help you in exercising:
Train While Fasting
If your major purpose is to lose weight but wish to have some muscle, you can do exercise to keep your body from burning muscle. Intermittent fasting can lead to the loss of lean muscle mass to power your daily activities.
Eating Before a Cardio Workout
This is essential if you’re trying to add muscle mass. There is a distinction between adding muscle mass and preserving muscle mass. As long as you’re eating enough protein before your fast and continuing to use your muscles, you’ll be fine even if you’re in a calorie deficit.
This is because fasting means your supply of rapid energy is limited. During a fasted workout, your body is looking for fuel from working out too hard or for too long and may potentially start breaking down more muscle.
Carbohydrates are the go-to choice for quick energy. But if there is a deficit of carbs, protein will provide the glucose to keep blood sugar levels even. However, this is an inefficient use of protein as it can help regulate your appetite and increase your muscle mass.
Eat Before You Lift Weights
Lifting weights, sprinting, CrossFit, and other high-intensity activities rely on carbohydrates for fuel. If you do any of these things during your fast, your performance might suffer. Instead of becoming more robust and quicker, you may become weaker and slower.
If you’re slimmer with less muscle mass to spare, you may arrange your lifting sessions during your feeding window. So, if you eat from midday to 8 p.m. every day, attempt to hit the gym at about 5, then go home and have a high-protein dinner to ensure appropriate healing.
Lifting weights after your meal window is also allowed (9 or 9:30 PM in this example). The protein you had before your workout will aid in muscle regeneration afterward.
Fast Before Cardio
Fasted cardio—jumping on a treadmill or cycling for 30 minutes or more before breakfast—is a muscle-chiseling strategy that many bodybuilders and other physique competitors swear by.
The research is divided on whether this activity burns faster than running after a meal. You may burn more fat in a fasting state if you keep that cardio activity low-intensity.
When Is It Better To Work Out?
Intermittent Fasting And Working Out In The Morning
This is the most excellent option because it will help your circadian rhythm. Doing your activities near the end of your fasting time is also preferable, allowing you to eat afterward.
It will be difficult to exercise after a lengthy period of not eating, but you will grow used to it. You can adjust the intensity of your workout to how your body feels.
Intermittent Fasting And Working Out At Night
Training sessions that are too close to bedtime are not recommended because they may impair the quality of your sleep.
Will Exercise While Intermittent Fasting Improve Performance?
While some people exercise to burn calories, others exercise to achieve fitness goals.
There are questions if combining intermittent fasting with exercise can help improve performance or if more intense workouts while fasting could jeopardize fitness goals. Scientists have attempted to answer these and other questions, but the results have been equivocal thus far.
On the one hand, several studies reported no differences in performance when subjects were fasted or fed. Athletes who practiced intermittent fasting did not perform any better than fed athletes in shorter exercise routines (under 60 minutes).
In the study, they did not run faster or execute more reps per training session. A similar thing happened with aerobic exercise: intermittent fasting did not reduce performance but did not improve it either. However, working out after a long fast has been shown in certain studies to degrade performance6.
How Might Intermittent Fasting And Exercise Be Ineffective?
According to research, exercise during fasting has also been related to certain potentially negative side effects. These could include:
Struggle To Build Muscle
In a 2018 randomized control trial, it discovered that males who did IF gained less muscle than those who ate regular meals. However, IF did not affect muscle retention or muscular improvements7.
Both IF and exercise have been shown to lower blood pressure. When combined, you may suffer lightheadedness due to reduced blood pressure8.
Blood Sugar Levels
Low blood sugar levels may decline due to IF and exercise. You may feel faint if your sugar levels fall too low.
It might be uncommon, but fasting may cause you to experience hypoglycemia or low blood sugar. If you have diabetes, this can potentially be dangerous since diabetes medications already put you at risk for low blood sugar.
Tips And Tricks When Exercising While Fasting
- Keep hydrated! This is especially vital if you work out immediately after waking up. You’ll be slightly dehydrated after a night of sleeping, and dehydration is the enemy of performance and fat oxidation.
- A cup or two of black coffee improves performance and aids fat loss during fasting cardio. If you’re feeling sluggish, this is a terrific pick-me-up.
- Pay attention to your body. Exercising while fasting is not for everyone. Especially in an intense workout. If you’re not feeling well, reduce your intensity or take a rest. Don’t do it if you find it difficult to adjust.
- If you’re fasting for more than 24 hours, stick to low- to moderate-intensity aerobic sessions.
- It’s a good idea to break your fast sooner rather than later after intensive workouts on an empty stomach at least if you exercise several days a week and want to restore the energy particularly when you feel weak.
Intermittent fasting and exercise are doable and can be a great combination when done right. They have numerous advantages on their own and while both provide you with benefits, it is not mandatory that you incorporate them together if your goal is to achieve your weight loss.
See what works best for you. Try and experiment with different workout plans to see what you can maintain, and always trust that your body is telling you what it can handle.
1 Marinac CR, Nelson SH, Breen CI, Hartman SJ, Natarajan L, Pierce JP, Flatt SW, Sears DD, Patterson RE. Prolonged Nightly Fasting and Breast Cancer Prognosis. JAMA Oncol. 2016 Aug 1;2(8):1049-55. doi: 10.1001/jamaoncol.2016.0164. PMID: 27032109; PMCID: PMC4982776.
2 Vieira, A., Costa, R., Macedo, R., Coconcelli, L., & Kruel, L. (2016). Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: A systematic review and meta-analysis. British Journal of Nutrition, 116(7), 1153-1164. doi:10.1017/S0007114516003160
3 Jaspers, R.T., Zillikens, M.C., Friesema, E.C.H., delli Paoli, G., Bloch, W., Uitterlinden, A.G., Goglia, F., Lanni, A. and de Lange, P. (2017), Exercise, fasting, and mimetics: toward beneficial combinations?. The FASEB Journal, 31: 14-28. https://doi.org/10.1096/fj.201600652r
4 Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG 3rd, Leeuwenburgh C, Mattson MP. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018 Feb;26(2):254-268. doi: 10.1002/oby.22065. Epub 2017 Oct 31. PMID: 29086496; PMCID: PMC5783752.
5 Garrison, L. (2020, February 28). Intermittent fasting can aid in weight loss, anti-aging and overall health. Minneapolis/St. Paul Business Journal. https://www.bizjournals.com/twincities/news/2020/02/28/intermittent-fasting-can-aid-in-weight-loss-anti.html
6 Zouhal H, Saeidi A, Salhi A, Li H, Essop MF, Laher I, Rhibi F, Amani-Shalamzari S, Ben Abderrahman A. Exercise Training and Fasting: Current Insights. Open Access J Sports Med. 2020 Jan 21;11:1-28. doi: 10.2147/OAJSM.S224919. PMID: 32021500; PMCID: PMC6983467.
7 Tinsley GM, Forsse JS, Butler NK, Paoli A, Bane AA, La Bounty PM, Morgan GB, Grandjean PW. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. Eur J Sport Sci. 2017 Mar;17(2):200-207. doi: 10.1080/17461391.2016.1223173. Epub 2016 Aug 22. PMID: 27550719.
8 Malinowski B, Zalewska K, Węsierska A, Sokołowska MM, Socha M, Liczner G, Pawlak-Osińska K, Wiciński M. Intermittent Fasting in Cardiovascular Disorders-An Overview. Nutrients. 2019 Mar 20;11(3):673. doi: 10.3390/nu11030673. PMID: 30897855; PMCID: PMC6471315.