MYTH: Fasting Will Ruin My Metabolism


Let’s take a look at another one of the myths that surround fasting. 

You can find some of our previous myth debunking articles here, if you missed it. 

The idea that fasting will somehow mess up your metabolism is probably one of the most wide-spread myths out there. 

Let’s talk about why it’s not true, and what the truth really is. 

What is metabolism anyway?

When we talk about metabolism, we’re talking about the chemical process in your cells that converts food you consume into energy.

Your metabolic rate reflects how efficient (or not) your body is at that process. 

Simply put, it’s how well you burn energy.

Fasting increases metabolism 

Not only does fasting NOT mess up your metabolism, it actually ramps it up.

When you fast, insulin (fat storing hormone) drops. 

When insulin goes down, other hormones, such as adrenaline and HGH, go up. 

And those hormones speed up your metabolism. 

Think about it, fasting is a stress to the body. A good stress, but still a stress.

In response to that stress, your body is not going to slow down your metabolism, it’s going to speed it up. 

As Dr. Fung often says, “Your body is just not that stupid.”

Now that we know fasting will not slow down your metabolism, let’s look at some things that can.

Yo-yo dieting and calorie restriction

By the time we get to the fasting lifestyle, many of us have gone through just about every diet out there.

And these diets work temporarily because they limit your calories.

But what always happens? 

The weight you lost comes back, and most of the time with even more weight.

But fasting is different. Fasting is NOT calorie restriction.

That sounds odd, right? But taking in no calories is not the same as taking in less calories

What’s the difference, you ask?


Even if you only ate 500 calories a day, you would still release insulin. 

And insulin tells your body to store fat. 

During fasting, insulin levels are not spiked, so you move into burning fat, instead of storing it. 

What does all this have to do with metabolism? 

If you are eating around the clock, even if you’re eating less, insulin prevents you from tapping into your stored fat.

Therefore your metabolism will now drop to match the amount of calories you’re taking in, because that’s where your energy is coming from. 

But with fasting, the energy is not coming from calories, it’s coming from your stored fat.

So the metabolism doesn’t have to drop. 

Make sense? 

But that’s not all …

There are other things that can slow down your metabolism, even when you’re fasting.

Poor sleep

Not getting enough quality sleep makes it harder for your body to do the things it needs to do, including burning fat. 

Most people need at least seven hours of sleep a night. 

In today’s busy world, we don’t always get that, but it’s something to aim for.

Turning off your electronics and dimming the lights a few hours before bedtime can help. 

Excessive or strenuous exercise

Too much exercise can keep cortisol levels raised, and sabotage your fat burning efforts, especially if you’re already overweight. 

If you’re more than 40 pounds overweight, gentle exercise is better. Walking is great!

Doing the same thing 

Even with fasting, it’s a good idea to switch things up.

If you regularly do Extended Fasting, take a break sometimes and try some Intermittent Fasting.

If you are an Intermittent Faster, switch up your schedule every now and then, or try Extended Fasting.

This is what we call “metabolic confusion” … it keeps your body guessing so it doesn’t settle into a weight loss stall. 

Too much Extended Fasting

Doing long fasts over and over, and not doing proper refeeding in between, will eventually take a toll on your metabolism. 

Take time off from Extended Fasting and do Intermittent Fasting for a while. 

And make sure you always follow proper refeeding guidelines after your Extended Fasting. 

Medical conditions and medications can affect metabolism

  • Metabolic diseases such as type 2 diabetes (fasting will fix that!)
  • Some inherited medical conditions
  • Thyroid issues 
  • Some medications

Fasting is good for you and your metabolism!

Don’t let a myth stop you from experiencing the amazing health and weight loss benefits of fasting. 

Happy Fasting!

Author: Roo Black

Roo Black

Roo is a fasting coach with over 5 years of experience. She leads the admin team of the Official Fasting for Weight Loss Facebook group – one of the largest fasting communities on social media with over 125,000 members. We highly recommend this group for anyone who is looking for fasting advice or coaching.

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