Why Fasting Works Better for Weight Loss Than Counting Calories

Why Fasting Is Better for Weight Loss than Counting Calories

For decades, we’ve been told to “eat less, move more”.  

In other words, create a “negative energy balance” in your body, and you’ll lose weight.

That’s basically what they taught me in medical school, and PA school.  So I assumed it was right.  

I’ve since learned better. 🙂

Today I’ll share with you why fasting is actually much more effective than just counting calories if your goal is to reduce body fat.  

For the whole story, read on. 

First, What Happens If You Eat All Day Long?

People used to eat 3 meals a day.  Now, most people eat a lot more often than that.  

Turns out, eating all day long is not a great way to lose weight (even if you reduce calories).    

Here’s why:  

After each meal, your blood sugar goes up for a while, and so does a hormone called “insulin”.  

eating 3 meals a day tends to raise insulin and make you fat

Insulin goes up whenever you eat carbs, and it helps bring your blood sugar back down. Insulin also tells your body to store food energy as fat.

Assuming you’re eating a somewhat typical American diet (which has tons of processed carbs), you’ll get a big spike of blood sugar and insulin after each meal.  Then it takes a few hours or so for your levels to come back down.

And if you have other snacks or drinks in between…your blood sugar and insulin basically never come down.  

Having Persistently High Insulin Makes You Fat

If you’re eating like this, your blood sugar and insulin stay fairly high throughout the day. 

Why does this matter?

Whenever your insulin is high, your body fat is “locked away”, and can’t be used as fuel.  

So it just sits there, and slowly gets bigger. 😉

How “Intermittent” Fasting Helps you Lose Weight

“Intermittent fasting” (IF) usually refers to shortening your eating window on a daily basis.  

That’s why it’s also called time-restricted eating (TRE).

For example, if you eat all your food between 10 a.m. and 6 p.m., that’s an 8-hour eating window.

Time-Restricted Eating Makes it Easier to Burn Fat

So what’s different in your body during TRE, versus a “normal” day?

Let’s use the popular 16/8 daily schedule as an example.

If you eat during just 8 hours (instead of eating all day long), there’s more time for your blood sugar and insulin to come down to normal levels. 

Intermittent fasting helps you burn more fat and lose weight

When your insulin level comes down, that makes it possible to use your own body fat as fuel.  The lower insulin level releases your fat, in a sense (thanks to an enzyme called “hormone-sensitive lipase”).

That’s the key reason why daily TRE / IF can help you burn more fat, and potentially lose weight.  

TRE + Keto Is Even Better for Fat Loss 

Ketones are the alternative energy source your brain and body use (instead of sugar) when you fast for a while.  Your liver makes ketones out of fat.  

Other than fasting, another way to stimulate ketone production in your liver is to eat a lot of fat (and avoid carbs).  

Hence, the “keto-genic” diet.

Now, let’s take the same scenario as above (16/8 TRE).  But instead of eating a Standard American Diet (S.A.D.) during your eating window, what if you tried eating low carb / high fat instead?

Well, here’s what that could look like:

Intermittent fasting plus a ketogenic diet helps you burn even more fat

Since you’re not eating carbs, your blood sugar and insulin won’t go up nearly as much after each meal.

And since insulin stays low most of the time, you’ll be able to access your own body fat more readily.

That’s why eating a ketogenic diet makes it easier to burn body fat.  

As a bonus, ketones also help suppress your appetite.  

I’ve found I don’t get as many cravings for sugary processed foods when I’m eating a ketogenic diet, and that’s probably a major reason why.  

More Ways Ketones Help You Reduce Body Fat

Ketones do some other fancy things as well, which can help you burn off even more fat.

Ketones Activate “Brown Fat”

I recently learned that ketones activate something called brown adipose tissue, or “brown fat”.

Babies have a lot of brown fat, but adults have some as well.

Basically your body uses brown fat to produce heat.  So naturally, it gets activated by cold exposure.

But ketones also stimulate brown fat, which means you’ll burn off more energy just by having high ketones.

Ketones “Carry” Energy (i.e. Calories) Out Of Your Body

You may have noticed that weird fruity smell on someone’s breath when they have high ketones.

The reason it smells that way is ‘cause they’re breathing off acetone (one of the three main types of ketones in your body).

Stop and think about that for a second.

They’re actually breathing out ketones.  Like fat or sugar, ketones contain energy.  So when your ketones are high, calories literally waft away with every breath you take.

You also pee out some of your ketones when they’re high. So that’s another route of escape that lets you get rid of even more fat.

If you think about it, having high ketones is like a natural form of liposuction. 🙂 

It Doesn’t Work Unless You Actually Do It

Quick side-note about keto:

I’ve met a LOT of people that say they’re “doing keto”, but they aren’t really. That’s because they eat too many carbs, and they don’t measure their ketones.

Don’t be that person. 🙂

If you wanna try keto:

  1. Measure your ketones at least once a day (cheap urine strips are fine as a beginner)
  2. Consistently track how many grams of carbs you eat each day

Otherwise, you may accidentally be eating high fat and high carb at the same time, which can do more harm than good.

Extended Fasting Can Be Even Better for Weight Loss

Time-restricted eating gets your insulin down for a while each day, and that helps you burn more body fat.  

Eating a ketogenic diet also lowers your insulin, which makes it even easier to access your body fat as fuel.  And having high ketones actually “escorts” more fat out of your body, through your breath and urine.  

In addition to all of that, multi-day “extended” fasting gives you some other advantages when it comes to fat loss. 

And for some people (not everyone), extended fasting is practically a necessity to get any real sustained weight loss.

To understand why, keep reading.  

Extended Fasting Maximizes Your Fat Burning

Multi-day fasting gets your insulin level even lower than TRE, and keeps it down longer.

It takes a couple days for your insulin to really come down all the way.  And that’s when you burn fat the fastest. 

Extended fasting maximizes fat burning 3 21

As long as you keep fasting, your insulin level stays nice and low.  So you keep burning fat at the maximum rate.

If you have a lot of extra body fat, extended fasting is a great way to accelerate your weight loss.   

Longer Fasts Can Also Heal Your “Insulin Resistance”

Most American adults have persistently elevated insulin.  That’s another way of saying they have something called “insulin resistance”.  

What is Insulin Resistance?

If you eat sugar and processed carbs several times a day, your insulin stays high. And when insulin is high all the time, after a while it doesn’t work so well. So your pancreas has to pump out more and more insulin to get the job done.  

It’s a vicious cycle.  And it means you’re on the fast track to getting type 2 diabetes. 

Most likely, you’ve never had your insulin level checked.  Typically, doctors don’t order insulin blood tests, because it’s more expensive and may not be covered by insurance.

But if you’re overweight, it’s almost a guarantee that your insulin is higher than it should be.

High blood pressure is another telltale sign. And sometime you can have skin changes too–as explained by Dr. Bikman in the video below:

Correcting Insulin Resistance Helps you Lose Weight Faster

Recall from above that whenever your insulin is high, you can’t burn body fat. 

If you have insulin resistance, that means your insulin is persistently high.  So it’s almost like you can never burn any body fat.  

Obviously, that makes weight loss pretty hard.  

For garden variety insulin resistance, daily TRE (or eating a low-carb diet) may be enough to significantly improve your insulin levels.

But if you’ve had insulin resistance for a long time, it can get pretty “entrenched”.  And you may need to do some longer fasts to get over the hump, or break through plateaus.

Basically, longer fasts give your insulin some extra time to come down, which tends to improve its function and sensitivity.  

Prolonged fasting also helps you clear out fatty deposits in your liver and pancreas, which makes those organs work a lot better.  And that improves insulin sensitivity as well.

Bottom line?

For some people, extended fasting is the best way to lose weight.  That’s because it not only maximizes fat burning, it can also help correct insulin resistance — a common reason for plateauing.  

Will I Lose Muscle Weight From Prolonged Fasting?

Some people worry about losing lean body mass (including muscle) when they fast, but the opposite is actually true-

Fasting doesn’t burn muscle, but actually helps preserve it through a few different mechanisms. Compared to fasting, you’re more likely to lose muscle and other lean body weight when you cut calories (though exercise mitigates this pretty well).

Don’t Rush This Fasting Thing

Since I’ve been talking about the benefits of extended fasting, here’s a quick reminder–

If you haven’t done a lot of fasting before, think of it like starting a new workout regimen.

You wouldn’t go out there and squat 1,000 pounds on the first day.  Instead, you would start off pretty easy, and gradually increase intensity.  

Similarly, you need to strengthen your “fasting muscle” little by little.

As your body adapts, it’ll get easier over time.  

There’s no need to rush.  

Why Counting Calories is NOT the Best Way to Lose Weight

In the sections above, I explained that lowering insulin is key to weight loss (and how fasting helps you do that).

The problem with just reducing calories is that you may not lower your insulin very much.

And if you don’t lower your insulin, you can’t really burn off any body fat.  It’ll still be under lock-and-key. 

Here’s the thing-

It’s entirely possible to reduce calories but still eat a lot of processed sugar / carbs throughout the day.  Think of someone who lives on cereal, for example.  

Small frequent meals raise insulin and prevent weight loss

By eating small sugary or carby meals throughout the day, you’ll have frequent bursts of insulin.  So your insulin level will never really come down to normal.

If insulin stays high, you can’t burn much body fat.  That’s why calorie restriction alone is not a great way to reduce body fat.  

Daily Calorie Restriction Slows Down Your Metabolism

Another problem with just cutting calories is that it usually slows down your metabolism.

Here’s a typical scenario –

Let’s say you normally eat 2000 calories a day.  But you’re overweight, so you decide to cut it down to 1,500 calories per day.

At first, you lose some weight. But pretty soon your body realizes there are only 1,500 calories coming in every day.  So obviously it has to make an adjustment, or after a while you would starve to death.  

Since you’re only eating 1,500 calories per day, your body gradually shifts down to only burning 1,500 calories each day.  In other words, it slows down your metabolism.

And your weight loss plateaus.  

As a bonus, you feel crappy and fatigued, because you don’t have as much energy as you used to.  So you probably give up on your diet.  

With your now-slower metabolism, your weight quickly rebounds as well.  

In a nutshell, that’s why most calorie-restriction diets fail, and may even do more harm than good.

In Contrast, Fasting Doesn’t Slow Down Your Metabolism

Here’s the thing about fasting-

You don’t do it forever.

In other words, you don’t eat the same amount of food every day, like clockwork. So you keep your body guessing.

In between fasts, you FEAST.  And that sends a signal to your body that plenty of food is available. 

Perhaps even more importantly, when you’re fasting and your insulin is low, you have TONS of fuel available – in the form of body fat.  

So your energy level stays high (at least once you get used to it), and your metabolism stays solid.

That’s how we evolved, and our bodies know how to handle it.  

Do Calories Matter At All?

Yes, of course they do.  

Just not nearly as much as most people think.

When it comes to controlling body fat, hormones are MUCH more important than the number of calories you eat.

And the most important of those hormones is insulin.


If you eat all the time (like most people do), you tend to get fat.  Especially if you eat a lot of sugar and other processed carbs.  

Daily time-restricted eating (a.k.a. intermittent fasting) helps you burn body fat by lowering insulin for periods of time.  

Eating a low-carb, high-fat “ketogenic” diet further augments your ability to burn body fat, in a few different ways.  

Multi-day “extended” fasts are also a valuable tool for weight loss.  Not only do they create a more profound transition from sugar-burning to fat-burning, they can also make your organs work better and reduce “insulin resistance”.    

Now that you understand WHY fasting works well for weight loss, it’s time to learn HOW.

In a separate article, I explained a practical framework for how you can lose weight by fasting, step-by-step.

It’s not a “quick fix”. But if you do it the way I explained, it’s just about foolproof. 🙂

So give it a read, write down your plan, and then start today by taking one simple step!

🎧 Get Step-by-Step Guidance on The FastingWell Podcast!

I recently launched a podcast.

My main goal is help you get a smooth start with fasting, even if you’re a total beginner! 😃

I don’t run any ads….but I DO explain how to be successful from day 1.

SUBSCRIBE on your favorite platform! 👇👇

(You can also just search “FastingWell” on any app.)

Hope it helps!

Picture of Ben Tanner, PA-C

Ben Tanner, PA-C

Ben has been practicing as a physician assistant (PA, or PA-C, similar to a doctor) in emergency medicine, urgent care, and family practice since 2014. Since 2016, he has developed an avid interest in various forms of fasting, using it to improve his own health while helping friends, family, and patients do the same.