Fasting and exercise are two major aspects of cultivating a healthy lifestyle, but should you combine them? I’m here today to answer all your questions regarding exercising while fasting. We will explore the benefits of exercising in a fasted state, including the difference between cardio, burst training, and weight training, as well as some simple tips on how to implement it reap the most benefits of your fasted workouts.
Is It OK To Exercise While Fasting?
It is OK to workout while fasting because the key to weight loss and muscle gain is not calories or exercise, but hormone optimization. The studies demonstrate incredible benefits to daily intermittent fasting alone, but combining fasting with burst training takes the benefits of both to a whole new level. Combining the techniques raises growth hormone and makes you more hormone sensitive, which is the key to staying youthful, and lean.
Many people dwell on calories in/ out, and fear the impact of muscle loss that theoretically occurs when you exercise without having recently refueled, but when you understand the beneficial impact that exercising during a fasted state has on the body’s hormones, you’ll see that fasting and exercise aren’t only OK, they are actually the ultimate way to boost your health and body composition.
Is It OK To Exercise on an Empty Stomach?
Not only is it OK to exercise on an empty stomach, but it actually increases the benefits of exercise and of fasting. I call this a Multi-Therapeutic Approach (MTA), whereby the synergy of two things that are health promoting, actually boost each others benefits to a level they couldn’t reach as isolated therapies.
One of the best ways to take advantage of these benefits is working out in the morning before breakfast.
Intermittent Fasting and Working Out
Working out before breakfast is another way of saying that you exercise during your intermittent fasting period. An intermittent fast is the daily portion within the 24-hour clock that your body goes without food (including the period in which you sleep). The IF window begins when you consume your last bite or food or drink (other than water) before bed, and ends the following day when you take your first bite of food.
To reap the most benefits, the length of your intermittent fast should be between the 16 to 18 hour range. This means, for example, eating between the hours of 10:30am and 6:30pm.
When to Workout While Intermittent Fasting
The best time to workout while intermittent fasting is likely upon waking, or shortly after, to support the body’s natural circadian rhythm. Studies show that exercising (or eating) too close to bedtime can interrupt levels of deep and REM sleep, so best save it for the following day.
Ideally you don’t want to eat directly after a workout, for the same reasons you’re exercising in a fasted state: hormone optimization. Studies show even waiting 2-3 hours after a workout before eating promotes a rise in growth hormone (the fitness hormone), which helps to make you a fat burner and replace the used energy (sugar). It’s all about survival and energy conservation; adaptation to the stress created from a high intensity workout is the reason a hormone shift occurs. We are simply taking advantage of the body’s innate response for survival.
If your schedule only permits a lunchtime workout, you can exercise in your available time, and then benefit from the hormonal boost by refraining from eating until 2-3 hours after your finish exercising.
Cardio While Intermittent Fasting
The hormonal benefits you reap while exercising in a fasted state have to do with the depleted glycogen stores that occur when you fast. Doing cardio while intermittent fasting is OK, but your performance will hinge on how fat-adapted your body is (how good it is at burning fat for fuel, instead of glucose). If you’re new to fasting and exercise, you can expect your performance to drop a little (stamina, etc); it can take up to 6 months for some athletes to fully adapt their endurance to this new fuel source. Ie. If you’re a competing athlete, and your race results are your primary goal, don’t switch to fasted training a couple of weeks before a competition.
If you are doing cardio in a fasted state, avoid extending the fast post-workout, and opt instead to re-fuel right when you finish.
Burst Training and Intermittent Fasting
Burst training (also known as high intensity interval training, or HIIT) involves as little as four minutes of intense activity combined with rest for a total of only around 20 minutes. Not only is it time efficient, but studies show that burst training provides a high degree health benefits that you cannot get from aerobic exercises, such as the tremendous boost of human growth hormone (HGH).
The benefits of burst training include the ability to turn back the biological clock in your muscles and brain, to boost growth hormone, improve body composition, boost brain function, boost testosterone levels, and prevent depression. The benefits of using burst training while intermittent fasting increases all these benefits. Burst training is the optimal exercise method to incorporate into your fasted period, and to increase the benefits even more, you should continue to fast 2-3 hours post-workout.
Should You Lift Weights While Fasting?
In short yes it is OK to lift weights while fasting, but you need to be mindful here too of the role that glucose plays in repairing your muscles after a major weight lifting session, especially while in a fasted state.
When you exercise in a fasted state, your glycogen stores are already depleted. If your workout for the day involves heavy lifting, you can do so in a fasted state, but you should prioritise a meal immediately following your workout. Unlike a burst exercise session, heavy lifting puts enough stress on the body to warrant an immediate re-feed. Like a cardio session, a lifting session while fasted might negatively impact your performance in the short run, as your body adapts to being a ‘fat burner’. For this reason you may want to save your weight lifting sessions for periods after you have eaten (in which case you can fast for 2-3 hours post-workout), and incorporate fasted exercise on the days when you perform burst-style training.
Working out While Fasting Plan
Monday
Intermittent fast from 7pm to 11am
30 minute burst training (while fasted) at 7:30am
Tuesday
Intermittent fast from 7pm to 11am
30 minute burst training (while fasted) at 7:30am
Wednesday
Intermittent fast from 7pm to 11am
60 minute weight lifting workout at noon (not fasted), but wait 2-3 hours before having the following meal
Thursday
Intermittent fast from 7pm to 11am
Rest day from exercise
Friday
Intermittent fast from 7pm to 11am
30 minute burst training (while fasted) at 7:30am
Saturday
Intermittent fast from 7pm to 11am
2 hour hike (low to medium intensity, long duration) at 9am, followed by breakfast
Sunday
Intermittent fast from 7pm to noon
30 minute burst training (while fasted) at 9am
Summary
- Exercise while fasting is not only OK, it’s highly beneficial for hormone optimization (which is the key to many health benefits, including improved body composition);
- You can maximize the benefits of burst training and intermittent fasting by combining the two, for a multi-therapeutic approach;
- Cardio and weight training can also be performed in a fasted state, but your performance may suffer slightly in the short term;
- The best time to incorporate exercise while fasting is early in the day, to match the body’s natural circadian rhythm;
- Unless you’re participating in a heavy weight session or endurance cardio, you can benefit hormonally from fasting after your workout too (for 2-3 hours).
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Good stuff! A pleasure to read as well (if you try to get this info from YouTube, brace yourself). Going for two 36 hour fasts in one week. I’ve been playing with this for probably a year now- it’s just too convenient. Instead of DOING something to get in better shape, you STOP DOING something. After my last one the hunger just isn’t coming back (I choked on a piece of lettuce and ended up having to vomit it up- lettuce is over – rated anyway) so that probably killed my hunger. Today was supposed to be a normal eating day but just wasn’t hungry. Ended up saying screw it, and got into the soda. So maybe I should just wait for the hunger to come back? ??
Hi James! Thanks for your support and glad you’re enjoying experimenting with fasting. Transition in and out of fasts with soft foods from the Cellular Healing diet, like high-fat smoothies, avocados, sweet potatoes, and blended soups. Your hunger should return to normal–just keep up with the healthy fats, quality protein, and lots of veggies!
I am thinking of attending in Atlanta seminar in April. My question for burst training and intermittent fast. I have been keto(2-3 mmol) and training for triathlon. I have seen great results with body fat and overall health but what is Dr pampas opinion on how to Taylor this for optimum performance in sport. I find that I have trouble reaching that top gear for speed with out some carbs. Can you add a few healthier carbs while exercising intensely without jeopardizing all the benefits of intermittent fasting and ketosis
Hi Dr. Chris,
Thanks for reaching out, hope to see you at the seminar! When Dr. Pompa is in full-blown ketosis, he is able to exercise intensely on a fasted stomach. If you need some quality carbs to reach peak performance, then perhaps you’re not fully fat-adapted. Try “back-loading” carbs at your evening meal to maintain intermittent fasting benefits, and see more on ketosis here:
Part 1: https://drpompa.com/additional-resources/health-tips/ketogenic-diet
Part 2: https://drpompa.com/additional-resources/health-tips/ketogenic-diet-troubleshooting
Such great info. I wanted to know: is there any suggestion on doing the fast day (in the example of doing it 1x/week) on a HIIT day or does it matter? Would it be better to do the fasting day on a non-exercise day?
Doing HIIT on a fasted stomach can really increase results, so yes give it a try! 🙂
I really appreciate the info that is being shared. I am 68 and have done an intermittent fast for about 8 months, working myself to a level of 17 to 20 hours, 5 days of the week. My sleep starts about 230am.
This means I basically have (1) 4 hour long meal each day. I start with 2 or 3 egg omelet when I wake after a 7 to 9 hour sleep. NO sugars of any kind until I have yogurt and cottage cheese about 2 hours later. Most days I am able to keep sugars to about 20-30gm, and protein 90-110gm, on 900-1100 calories. I have lost 70 lb in a year: aiming for 30 more to get to 163lb.
About every 3rd day I have a minimum 1hour walk, but often extend that to 10km(3 hours). I cant seem to do sprints at all: seems my legs are built for endurance and not speed.
Would you suggest when I should do walking? Generally I do it about 2-4 hours after my meal, depending on weather. Should I use a vibration plate if I cant HIIT?
Any kind of movement is great. When your body wants to move, go for it. No need to pre-plan time of day.