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Should You Try Fasted Exercise?

4 MIN READ • 4th August 2017

In case you didn’t get the memo, fasted cardio – exercising on an empty stomach – is being hyped as a fast way for fitness fans to lose weight. Celebrity trainer Tracy Anderson, who counts Gwyneth Paltrow, Kim Kardashian, Nicole Ritchie and Jennifer Aniston as loyal clients, is an advocate of the method, and rumour has it that pop queen Madonna has also tried it out.

If you’re aiming to lose weight, you may be interested in trying fasted exercise. However, it’s not for everyone. Find out what fasted exercise is and if it could work for you.

So, what’s the big deal?

“Fasting helps the body to burn more fat when doing cardio because it reduces the storage of insulin. A hormone that dampens fat burning,” reports Clare Goodwin, nutritionist and hormone specialist at “When insulin is high, our body is in ‘storing mode’ and can’t be in fat-burning mode. When we don’t eat for eight to 12 hours [such as overnight], insulin levels decrease and our body’s fat-burning ability increases.” If your stomach is rumbling at the very thought of it, read on.

Does it really work?

This is the million-dollar question as many of us are sceptical about working out before breakfast. But, this is the optimum time as our carbohydrate stores diminish overnight, which forces the body to use fat for exercise fuel. While fasted training can be handy for short-term results, experts note that it isn’t the only way to lose weight. “There is little evidence to suggest that fasted training is more effective than fed training in the long term,” argues Adam Howman, personal trainer at The Gym Brighton ( “It comes down to whether you like to train early in the morning before having a meal.” However, the immediate benefits of fasted cardio are backed by science. Research published in the British Journal of Nutrition shows that exercisers burned 20 percent more fat when performing fasted cardio than when exercising after having a meal.

Further data in the International Journal of Sports Nutrition and Exercise Metabolism reports that doing 36 minutes of moderate-intensity cardio (at 65 percent of maximum heart rate) before eating results in burning more calories in the 24 hours post-workout. “Studies have shown that those doing slow and steady cardio, HIIT-type cardio and endurance training have all benefited [in fat loss terms] from fasting,” concludes Clare. The results are worth shouting about but fasted cardio isn’t for everyone. Time to suss out whether it’s the right approach for you.

    • Should You Try Fasted Exercise?
    • Need a breakfast boost?

    • If you can’t go without your smashed avo on rye in the morning, exercising on empty may not appeal. Studies show that some people tire when working out sans food (possibly because they’re not in the right frame of mind for exercise).
      “Fasted cardio can feel a bit hard initially,” warns Clare. “If you’re used to exercising after eating, your body will be used to burning glycogen (carbohydrate) for energy. It can take a couple of weeks for the body to adapt to burning fatty acids instead, which can leave some feeling like they’re lacking energy.”

    • Should You Try Fasted Exercise?
    • Does food motivate you?

    • Fasted exercise may not be the best option for those who find that food increases their enthusiasm for working out in the morning. It’s great for exercisers who hate moving on a full tummy. “It comes down to personal preference,” agrees Owen Henderson, senior PT at Hall Personal Training. “If you’re prone to feeling sick when training after eating, a fasted workout may be beneficial.”

    • Should You Try Fasted Exercise?
    • Are you sleeping enough?

    • Weight loss 101 – skimping on sleep can undo the fat-burning benefits of exercise. Failing to clock the recommended seven hours can reduce insulin sensitivity. As well as increase food cravings. “If you don’t get enough sleep, tiredness will counteract the benefits you might get from fasted cardio,” agrees Clare. “Studies show that just one week of less than five hours per night worsens insulin sensitivity by 25 percent. I see it a lot – women work long hours and then get up early to go for a pre-breakfast run or gym session.” Take-home message? If you want to try fasted cardio, make sure you go to bed early.

    • Should You Try Fasted Exercise?
    • Do you want to build muscle?

    • Don’t turn to fasted exercise for help if you want to build muscle. “When weight training, your body uses stored carbohydrates in the form of glucose to fuel the activity,” explains Adam. “If you don’t have any, the body will turn to its next available fuel source. Which could be your lean muscle tissue”. Similarly, fasted cardio may not be the right choice if you have a specific (non-weight loss) performance goal. “I’d recommend doing an aerobic activity in the fasted state,” adds Adam. Choose something, such as jogging, incline walking, cycling or stepping that works your body at 60-75 percent of maximum heart rate for around 30-60 minutes.

If you are going to sweat sans food, pack a protein shake in your gym bag to avoid binge eating in the café after your workout.

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