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Health fads, workout trends and crazy diets come and go, but what about fasted cardio?

A long-running fitness trend, fasted cardio means you do cardio first thing in the morning on an empty stomach, before breakfast. It might sound insane to those that can’t imagine skipping breakfast or functioning without coffee, but tons of people are advocates for it.

What fasted cardio does to your body

By running, rowing or spinning (or whatever form of cardio you enjoy) right after waking up, the claim of fasted cardio is that your body is able to utilise fat storage (instead of food) for fuel. 

Some studies have agreed with this, but it is the conversion of fat into energy that results in fat loss. Your body has two stages of burning fat — breaking down fat molecules and converting them into energy. 

When you do not eat, your insulin levels go down, making it easier for your body to break down fat molecules instead of using carbohydrates from food. However, you can’t control whether the cells in your body get energy from glucose or fat when it uses its internal storage. 

This study published in the Journal of Applied Physiology reported that there was a decrease in exercise-induced glycogen breakdown during fasted cardio but fat oxidation during fed cardio (when you eat before a cardio workout) was the same.

How your body works after fasted cardio

Although fat oxidation is higher during a fasted cardio workout, it is usually higher during the rest of the day in people who do fed cardio. This study in the International Journal of Sport Nutrition and Exercise Metabolism concluded that there is little to no difference in doing fasted cardio, In fact, the authors recommend exercising after consuming a light meal.

Currently, there are limited clinical trials, tests and scientific research on the topic. The lack of in-depth testing also means that we are not sure about the long-term effects of fasted cardio. For instance, fasted cardio can be dangerous to your body, so be aware of the potential risks before you do it.

The bottom line

Sure, running on an empty stomach can make you feel lighter and faster. However, some people end up feeling lethargic and nauseous during a fasted cardio workout.

Instead of debating about fasted cardio, it’s more productive to look at what training style works best for you. Are you more of an AM or PM person? What sort of workouts would get you on your feet? Do you like it solo or in a group?

No matter what time of the day you train, remember that it’s important to have balanced meals to fuel your body.

Text: Carissa Wong / Shape