How Fasting Effects Your Metabolism (BMR)

A common misconception when it comes to fasting is that it would have a negative impact on our BMR (Basal Metabolic Rate) which in simpler terms is an estimate of how many calories your body burns in it’s rested state. The number represents how much energy your body requires for its basic functioning, such as breathing and keeping your heart beating.

It’s common for people to calculate their BMR using different calculators on the web when they’re planning on restricting their calories, as to know how many calories to cut from their diet.

A problem however when people start cutting calories heavily and go way below their BMR is that the body adapts to this change, actually lowering their basal metabolic rate. Contrary to popular belief, fasting does not. But more on that later.

Why is BMR interesting to us?

Our BMR makes up for the largest part of our energy consumption. The conception that fasting would put is in a “starvation”-mode that would lower our BMR is wide-spread and as the latest research have shown, completely false.

If you put your body in a state in which it slows down metabolism, you’ll end up with less overall energy and your weight loss will slow down.

Fasting and BMR

Dr. Jason Fung is a prominent figure when it comes to research about fasting. He has been propagating it as a method for his patients suffering with diabetes for keeping their diabetes in check, and been working with fasting for a long time.

He’s done a ton of research in the area and is usually the first source to encounter when getting into the subject. I’d recommend reading his book The Obesity Code if you are interested in getting down into the science, all explained in simple terms.

The Obesity Code, written by Jason Fung, MD.

In his book he explains what happens when you go on a caloric deficit. Basically your body will slow down your metabolism to save energy as it recognizes a deficit in the amount of energy your are consuming through eating. It also has a harder time accessing fat because of the insulin spikes caused by eating a diet consisting of carbohydrates (especially sugar).

However, if you are fasting or eating a low-carb diet, your body will turn into a state called ketosis in which is will start pulling fat out of your fat cells and turn it into energy.

As this does not spike your insulin, fasting or a low-carb diet has no reason to cause a lower metabolism as the body can always pull more energy from fat, eaten or as in a fasting state: from your body.

Fasting actually increases your BMR

A surprising fact about fasting is that it not only doesn’t slow down your metabolism, but is actually believed to increase your BMR the first 3 days. This claim requires more research to be completely proven, but Dr. Jason Fungs patients who have done fasts and been tested along the way have actually shown an increase in BMR.

In conclusion, fasting won’t slow down your metabolism as it puts you into a state of ketosis – which gives your body energy from your body fat in a steady rate. Avoiding insulin spikes and dips, which for all we know causes your body to slow down your metabolism. Fasting may also increase your BMR, making you burn fat as your fuel at an even higher rate. A win-win situation if I’ve ever seen one.

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