Working Out While Fasting: Why it's Good For You

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.