Let’s talk about all things fasting and exercise! What are the benefits of exercising in a fasted state? How do these benefits differ between different types of training? What are some tips to optimize these benefits?

Is It Good To Exercise While Intermittent Fasting?

It is good to workout while fasting! The key to losing weight and gaining muscle is not calories or exercise, but rather, working with our hormones. The studies demonstrate incredible benefits to daily, intermittent-fasting. But combining fasting with movement takes the benefits of both to a whole new level. Combining the techniques raises growth hormone levels, which is the key to staying young and healthy.

Many people dwell on calories in and out and fear the impact of muscle loss that theoretically occurs when you exercise without relentlessly re-fueling. Some people will eat protein around the clock every couple of hours. But—when you understand the beneficial impact that exercising during a fasted state has on your hormones, you’ll see that Intermittent Fasting (IF) and exercise aren’t only good, together—they are the best way to boost your health and body composition.

Is Good To Exercise on an Empty Stomach?

Not only is it good to exercise while intermittent fasting, but it increases the benefits you reap from the exercise. The synergy of this combination will bring the benefits of both to new heights.

How can you optimize these benefits best? You can do so by working out in the morning before breakfast and then holding off a few more hours before your first meal.

Intermittent Fasting and Exercising

Working out first thing in the morning (before eating) is another way of saying that you exercised during your intermittent fasting period. An intermittent fast is eating during a short window during the day.

The fast starts when you consume your last bite of food, before you go to sleep. The fast ends the following day when you consume your first bite of food.

The length of fasting varies for person to person, depending on your goals, body type, hormones, etc. Start by fasting for 16-18 hours. So you would eat between the hours of 10 am and 6 pm. Then you can tweak it from there, depending on your individual fasting needs and goals.

When is the best time to work out when fasting?

The most ideal time to workout while intermittent fasting is first thing in the morning, or shortly after, to support your body’s internal rhythm. Exercising too close to bedtime can interrupt levels of deep and REM sleep.

Wait 2-3 hours after working out before eating— this promotes a rise in growth hormone, which helps put you into a fat-burning state. 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 merely taking advantage of the body’s innate response to 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 can work, but your performance may be impacted if you are not in a fat-adapted state. 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 (fat). 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.

HIIT and Intermittent Fasting

HIIT or burst training 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 impressive benefits that you cannot get from other exercises, such as the tremendous boost of human growth hormone (HGH).

The benefits of burst training include slowing the aging process, a boost of growth hormone, improved body composition, boost in brain function, a gain of healthy hormone levels, and prevention of depression and anxiety. The benefits of using burst training while intermittent fasting increases all these benefits significantly. Burst training is the optimal exercise method to incorporate into your fasted period. But to increase the benefits more, continue to fast 2-3 hours after your burst session.

Should You Lift Weights While Fasting?

In short, yes, you can lift weights while fasting. But— be mindful here of the role that glucose plays in repairing your muscles after a significant weight lifting session, especially while in a fasted state.

When you exercise in a fasted state, your glycogen gets depleted. If your workout for the day involves heavy lifting, you can do so in a fasted state, but you should prioritize re-fueling after your workout, rather than waiting 2-3 hours.

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.

 Summary

• Exercise while fasting is not only useful, 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;
• 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 doing heavy weight lifting or endurance cardio, you can benefit hormonally from fasting after your workout (for 2-3 hours).

 

References:

Zouhal, Hassane et al. “Exercise Training and Fasting: Current Insights.” Open access journal of sports medicine vol. 11 1-28. 21 Jan. 2020, doi:10.2147/OAJSM.S224919

Bassuk SS, Manson JE. Epidemiological evidence for the role of physical activity in reducing risk of type 2 diabetes and cardiovascular disease. J Appl Physiol. 2005;99(3):1193–1204. 

Donnelly JE, Blair SN, Jakicic JM, Manore MM, Rankin JW, Smith BK; American College of Sports Medicine Position Stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Med Sci Sports Exerc. 2009;41(2):459–471. doi:10.1249/MSS.0b013e3181949333

Bhutani S, Klempel MC, Kroeger CM, Trepanowski JF, Varady KA. Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans. Obesity. 2013;21(7):1370–1379. doi:10.1002/oby.v21.7

Oh M, Kim S, An K-Y, et al. Effects of alternate day calorie restriction and exercise on cardio-metabolic risk factors in overweight and obese adults: an exploratory randomized controlled study. BMC Public Health. 2018;18(1):1124. doi:10.1186/s12889-018-6009-1