Does Fasting Slow Your Metabolism There are so many diets that focus on the timing of eating, you may wonder if extended fasting will slow your metabolism down. That’s a perfectly natural question to ask.  After all, if you’re going to go to the effort of trying to change your habits, the last thing you want to do is make your situation harder!

Will Fasting Slow Your Metabolism?

There are many myths about the way fasting will slow your metabolism. Some have to do with a misunderstanding of the body’s “starvation mode” and others are a misunderstanding of the way the body uses energy in the form of food calories.  Even science has been a bit hazy about what will speed up and slow down the metabolic rate.

It’s not an easy concept. There is no single factor that decides whether you will experience a fast or slow metabolic rate.  Looking directly at extended fasting though, it can slow your metabolism if it isn’t done properly.

It’s important to understand that cutting off food for extended periods of time isn’t the same as intermittent fasting (IF). IF will prescribe certain hours of the day or days of the week in which you can eat.  Extended periods without food go for much longer and, therefore, have a different impact on the body.

Long Periods Without Food

Starving yourself for periods longer than a day will change the impact on your body when compared to eating within an 8-hour window each day, for instance.  Longer spans of time will force your body to need to change the way it uses energy in order to keep up basic vital functions. In these cases, fasting will often slow your metabolism because easy energy is not available, and the body must rely on reserves.

In these cases, it’s not the act of fasting that will slow your metabolism as much as it is the extreme low-calorie intake.  When calorie consumption drops below a certain level, the body is required to shift to rely on backup energy sources.  This isn’t an easy process, even when there’s a lot of body fat available.

As a result, the metabolic rate slows down since body fat and muscle (yes, you will also burn muscle during an extended fast) are a clunkier energy source than food. This can cause periods of extreme fatigue and weakness, can make it difficult to think clearly or keep up physical activity, and lead to other unwanted symptoms as well.

Beyond slowing the metabolism, extended fasting can also lead to nutrient imbalances, temporary limited rapid weight loss followed by slower weight loss, and problems with skin, hair, teeth, and major organ systems.