Fasted Cardio - What Does The Science Say?

What does the science say?

Although several studies have found fasting cardio to slightly increase fat oxidation (lipolysis) during exercise, the scientific community is yet to fully support the effectiveness of the theory. There are several reasons behind this. First, fasted cardio has proven to have little impact on weight loss or overall body composition. This is due to the fact that exercise accounts for only 15-30% of your daily energy expenditure. Therefore, it has a relatively small impact on weight loss when compared to your diet.

Second, having more energy for an exercise results in longer workouts, which leads to an increased calorie expenditure. Because fasted cardio specifically aims to reduce the amount of energy available, it often leads to lower training intensity and volume. Both of which can significantly reduce the endurance and health benefits the exercise would normally have.

Third, fasting does not mean you automatically switch from glucose to burning fat. Research shows that your body may start breaking down protein instead, leading to further loss of muscle mass. For example, one study showed that running in a fasted state yielded twice as much protein breakdown in muscles than in a non-fasted state.

Resistance training in a fasted state has also shown similar effects of lower performance and increased breakdown of protein. This becomes especially apparent the more intense the exercise becomes.

Final thoughts

Although there is relatively little research about fasted cardio, it is important to remember that any exercise, whether in a fasted state or not, offers significant health benefits.

The theory behind fasted cardio theory claims that exercising on an empty stomach may have greater fat-burning effects – which it does. However, weight loss and reduction of body mass is likely a result of an overall calorie deficit, regardless of whether exercise is completed on a full stomach or not. Studies have shown that the most effective way to improve body composition is combining a healthy diet with a consistent exercise program.

Another thing to remember is that energy systems in your body work at all times, whether you are resting or not. Only their proportions may change depending on the intensity and duration of the exercise. So, strictly focusing on burning fat during the exercise may not lead to the results you are looking for. 

Most importantly, working out should not be just about counting calories or focusing on weight loss. There are tremendous physical, social, and mental benefits that exercising can provide you with. Perhaps the best advice to give is to find what you enjoy and try to do it consistently. 

Did you learn anything new about fasted cardio? Let us know in the comments.