Is Fasting Safe? Debunking 14 Myths About Fasting

Debunking 14 myths about fasting and keto

If you implemented fasting or keto in your everyday life and you’re getting the great benefits of it, you might want to spread the word. Since it’s such an amazing way to lose weight, feel good, relax your gut, etc. Plus all the many benefits you’ve read about it (Alzheimer, cancer, detox, etc.).

But if you’re like me, you might already have given up talking about fasting with friends and acquaintance, especially your 60 years old uncle who swears that, if you do hard work, you have to eat 3 big meals a day. Because people are amazingly reticent to these concepts.

Every time I try to talk about it, I get thrown at me a bunch of myths and pre-conceived ideas about it.

And you know what? Several years ago, I might have responded with the same stupid ideas. It’s like if people are offended that we’re advising a logical idea (eat less to lose weight), so they respond with stupid ones (eat 5 times a day).

What are the biggest myths about fasting? Fasting will put you in starvation mode, once you’ll start eating again you’ll regain everything, plus some, you’ll fall into hypoglycemia, you need glucose to survive, you’ll lose all your muscle, etc. And all that is so wrong, so immensely wrong that it pains me just to write it.

But really, all that is just a sample of the kind of myth people have in their head about fasting. Let me debunk those, one by one so that on your next family dinner, you’ll be able to shut their damn mouth… and convince them to try it!

1. You Will Not Go Into “Starvation Mode” When Fasting

That has to be the most idiotic myth of all. Fasting being equated to starvation. A person who is starving doesn’t have enough food to sustain itself on a daily basis.

If you’re starving you don’t know when you’ll eat your next meal. You’re most certainly malnourished, lacking minerals and essential nutrients, weak and skinny. Starving means you risk dying because you don’t have anything to eat.

Guess what? You need food to sustain your body energy expenditure. That’s right. But if you’re a healthy person, eating 3 times a day and suddenly decide (decide, not being forces) to not eat for a week, your body will be able to cope with it. It’ll burn all this delicious butt or belly fat you keep in your fat stores. That’s why we call them fat stores, isn’t it?

The hunger you’ll feel when starting a fast is not from starvation. It’s your body getting used to burning up energy from the fat cells in your body. It’s your brain coping with your habits and usual cravings.

And when you fast for seven days you know what? You won’t even feel hungry for most of the fast.

“Starvation mode” has nothing to do with fasting.

2. You Will Not Fall Into Hypoglycemia

Fasting will cause low blood sugar. In medical terms, low blood sugar is called hypoglycemia. That’s perfectly right. But it doesn’t mean you’ll collapse or die from hypoglycemia when fasting.

If you don’t have diabetes or other rare condition which could cause non-reactive hypoglycemia, you won’t have any health risks. And as I’ll talk about later, even diabetics can do fasting, it could even be reversed through fasting.

You can feel lightheaded, unwell, experience headaches when fasting. But there’s no risk to your health, these are normal side-effects of getting your body into ketosis. In that state, your body will start burning fat for energy rather than getting it from glucose absorption.

Same thing with nutrients or minerals deficiency, which can be a real thing on a prolonged fast. Again, not a risk to your health in 99% of the cases.

And if you feel unwell and think you’ll die (even though you won’t), just eat.

As a side note, I did a full article on the subject, where I answer all the questions you could have about fasting and hypoglycemia. Check it out!

3. You Will Not Regain All The Weight

This one you must have heard too. It’s a big one and kind of a lame excuse not to fast since fasting is way more than just losing weight in my opinion.

“If you fast for a week, your body will compensate for the lack of food by making you so hungry you’ll regain all the weight”

You'll regain all the weight afterwards
Sure, after a fast, you typically eat junk food and regain all your weight!

In fact, it’s the exact opposite. When I do one meal a day, for example, I always eat less on my one meal compared to days I eat two times.

After a prolonged fast, you generally eat even less. Feeling full pretty quickly (luckily since overeating after a long fast is a really bad idea), you’ll even find that you’ll generally eat less afterward.

When you eat again after a fast, the first thing your body will do is refill your glycogen stores. These are glucose stores your body makes in the liver, in order to keep energy it can access quickly for your brain and muscles.

Glycogen stores are around 2’000 calories. Once it’s replenished it will then start to produce fat, yes, but you’d have to overeat for that.

And you’ll find overeating difficult after a fast since it actually quickened your metabolism. Keep reading the article, I’ll cover the fast metabolism you get from fasting to help clear this part up.

4. Your Body Doesn’t Need Glucose To Function

Your body has a daily energy expenditure. It varies depending on your weight and muscles, but we usually say that a woman needs 2’000 calories a day and a man 2’500 calories.

The best way to get this energy is through carbs, right? Since your body will use the glucose to create glycogen stores in the liver for later use and some of the glucose will directly enter the mitochondria to give energy to your muscles, you need glucose to function.

Actually you don’t. Your liver doesn’t need a single gram of glucose. It’s perfectly able to produce glucose itself.

When you’re not absorbing glucose for energy, the liver will produce glucose through a process called gluconeogenesis. This will come from the breaking down of:

  • Proteins
  • Certain types of amino acids
  • Lipids
  • And other states in the liver (pyruvate, lactate)

So you might ask: in order to have any of this in my body, I need to have had glucose at an earlier stage, otherwise how is the body going to fill these stores?

As I said, the liver can metabolize protein for energy. If you eat 3 eggs, for example, this will create an insulin response (which you generally get from eating carbs), which will then turn the proteins into glucose to be used immediately for energy or put in your glycogen or fat stores.

5. Fasting Will Not Make You Lose Muscle

Tim Ferris, the guy behind bestsellers such as The 4-hour body or Tools of titans, often likes to experiment. He did a 7 day, medically supervised fast during which he wasn’t allowed to exercise or go out of the facility. He lost 12 pounds of muscle.

So, why is this a myth? Because any diet will make you lose some muscle, calory restriction being the worst one. And because Ferris tried another fast, this time exercising every day, for 10 days, and claimed to have lost zero pounds of muscle.

On a prolonged fast, around the second day, your body starts producing more human growth hormone. This hormone, upon other things, prevents your body from losing muscle. Do you know what also increases human growth hormone? Exercise. In short, if you keep exercising during your fast, you shouldn’t lose any muscle.

Another interesting element about muscles and fasting is leucine. When you fast, blood leucine levels are higher. Leucine is a key branched-chain amino acid which has an anabolic effect. Meaning it’ll help you keep lean body mass.

Moreover, leucine could have the same effect as getting proteins and carbs for muscle gain and it’s a good trigger for protein synthesis.

To illustrate why your body would preserve muscle on a fast, think about our ancestors, which had to hunt to get food. Sometimes, they couldn’t find anything to eat for several days, but they kept hunting every day.

The body is not stupid, it knows to preserve muscle in order to be strong and able to hunt. In short, to find the food you need to survive.

If you want to know more on the subject, check out my complete article on fasting and muscle gain.

6. You Will Have Lots Of Energy When Fasting

That one is dedicated to all the hard workers in the world who think that you need to eat 3 meals a day if you’re doing heavy-lifting, farming or any other activity requiring lots of energy.

Fasting can actually give you more energy throughout the day. Since your body on a fast is turning itself to ketones, rather than glucose. And ketones are the preferred fuel for the brain.

It’s well known that if entering ketosis can be hard, full ketosis will give you a great deal of energy, way more than a big meal could. You’ll be able to concentrate and focus more since your brain is now using its preferred fuel as energy.

And have you ever felt tired after a meal? Of course, you have, everybody has. Generally, after lunch, there’s always this moment of drowsiness, lack of concentration, etc. That’s your stomach, liver, digestive system, working hard to process what you ate.

If you fast, you won’t have these kinds of problems.

7. Being Hungry Doesn’t Mean You Have To Eat

Spoiler alert: you’re not hungry.

Most of the time we think we are hungry breaks down to one simple thing: habits. Here’s an experiment for you, if you’re used to eating three times a day. Try not to eat for a day. You’ll have a big reveal: you’ll be hungry in the morning when you usually eat breakfast, you’ll be hungry at noon when you usually get lunch and around dinner time.

Hunger comes from habits
Feeling hungry often comes more from the brain and less from your metabolism

It all depends on your habits. Since I stopped eating breakfast, I’m never hungry in the morning anymore. Two years ago I went to Canada for three weeks and I ate breakfast every morning. I first had to get used to being hungry upon waking up, then to do the opposite to get back to intermittent fasting.

You’ll feel some kind of hunger on a prolonged fast, coming from your habits but also because it’s easier for your body to get energy from the food you consume rather than from fat stores.

But once you start a prolonged fast, hunger will disappear completely after 3 or 4 days (for some people it can go up to 5). The next time you’re hungry will be the time you NEED to eat.

Hunger can also come from cravings (getting addicted to fructose) and also some conditions (obesity, diabetes, insulin resistance) which will mess up the hunger hormone (ghrelin) or satiety hormone (leptin).

8. Breakfast Is Not The Most Important Meal Of The Day

The idea behind this is that by eating right after waking up you’re actually storing food as energy for the rest of the day. This way you’ll use this energy throughout the day as the main source. Meaning you should eat less in the evening.

This idea sounds perfectly fine, although when it comes to actual studies, there is no proof of any of that.

Fasting or intermittent fasting doesn’t necessarily mean you should skip breakfast. You could skip lunch. Or dinner. Or eat three meals within 6 to 8 hours (good luck with that). Intermittent fasting means restraining your eating window and fasting for the longest possible time in order to use your fat as energy.

But skipping breakfast is by far the easiest: you’ve already spent 8 to 10 hours fasting after dinner and during your sleep, what’re 8 more hours gonna do?

Moreover, when you start eating in the morning, that starts your digestive system and tells your body that you entered an eating window. Which could make you more hungry during the day and more prone to snack in the morning.

When fasting, the most important meal is not breakfast. It’s the one when you actually break your fast.

9. You Should Not Be Eating Small Amounts 5 Times A Day

That has to be a crazy idea. To lose weight, eat all the time. It’s like saying to alcoholics they should drink really small amounts of beer 5 or 6 times a day.

The idea behind that is that when eating really often you won’t ever feel hungry (except you’ll be craving food constantly) and it’ll increase your metabolic rate.

Your metabolic rate is the number of calories your body can burn within a given time. What cultivated this myth (because it’s a big myth) that eating frequently increases metabolic rate is that when you digesting food, it does increase, yes. But this only comes from the thermic effect of food.

So, eating 5 times 500 calories in a day will have exactly the same thermic effect as one 2500 calories meal, since that’s the total amount of food you digest that causes this thermic effect.

Multiple studies exist on this subject, explaining eating frequently won’t increase metabolic rate and promote weight loss.

10. Eating Fat Does Not Make You Fat

Eating fat with carbs will make you fat. Or fat with too much protein will make you fat. But plain fat, won’t make you fat.

To gain weight, your body needs to have an insulin reaction, since it’s the hormone responsible for creating fat stores. Here you can see the insulin response to the protein, fat, and carbs.

Insulin response to protein, fat & carbs
Insulin response to protein, fat & carbs –

Meaning if you eat plain coconut oil or butter with nothing else, the fat won’t raise much of an insulin reaction. But if you eat bread with butter, you’ll get a reaction from the carbs and the insulin will also use the fat in the butter to make fat stores.

So, in very short, eating fat will only make you fat in combination with carbohydrates or enough proteins.

11. Fasting Will Not Slow Down Your Metabolism

No, it doesn’t. Actually fasting has been proven to increase your metabolism. In a way, when you’re fasting, you’re training your body to lose fat.

Fasting increasing metabolic rates comes from increased norepinephrine blood levels, which in turn stimulates metabolism to break down body fat. Studies show that a 2 day fast could boost your metabolism to up to 14%.

But it seems that this effect decreases over a longer fasting period, most of the metabolism increasing effects happen during the first two to three days.

12. You Should Not Just Exercise And Eat Fewer Calories To Lose Weight

That’s what we might call the elephant in the room, THE diet everybody is advising to everybody, every practitioner on earth must have once advised a patient to “eat fewer calories and exercise more” to lose weight.

Except there’s one small little problem: it doesn’t work.

I could do a whole article on why calorie deficit and exercise doesn’t cause weight loss, but I would rather advise you to read the awesome Obesity Code from Jason Fung, which details why this infamous diet doesn’t work.

First, counting calories doesn’t work because, despite what everybody seems to think, a calorie is not a calorie. 200 calories of broccoli are not the same as 200 calories of chocolate. It’s not metabolized the same way, it won’t have the same effect on your body.

Second, it won’t work in the long term. If you need 2000 calories a day, but suddenly decide to eat 1500 to lose weight, your body will, in fact, make you lose weight. First and foremost by eating at your muscle (they’re the ones using up most of your energy), then tackling your fat.

But when you’re at 1500, what do you do? Drop to 1000? Do you know what your very smart, protective body will do? It’ll try to run on a 1000 calories by slowing down your metabolism. This means it will actually train itself to burn fewer calories to protect you. This means once you start eating again, you’ll regain weight faster since your metabolism will burn fewer calories.

Remember, your body is very old machinery. If you spend six months eating very small amounts every day, it will think you’re in a harsh environment where food is scarce. So it’ll try to protect you by using up your muscles and burning fewer calories (making you cold, more prone to disease, tired, etc.)

About exercise, have you tried running 20 kilometers? How many calories did you burn? Pretty depressing no? Exercise won’t account for much of your calorie expenditure. So, exercising to burn calories is a lost cause, adding to that that simple calorie deficit, as I said before, won’t cut it, this diet is already in bad shape.

Exercising won't make you lose weight
You shouldn’t exercise to lose weight, but for everything else

Exercising will make you lose water, exercising will make you gain muscle, muscles have mitochondria and mitochondria burns energy. But that won’t mean you’ll lose weight. Muscle being heavier than fat, you might even gain some (but that’s good though).

The idea here is that you’ll create more muscle, so your body will need more calories to function, and if you’re doing the calorie restriction diet, which doesn’t work, it might get easier. Except gaining muscle on calorie restriction can be quite hard!

That’s what we call a nice loop. And really baffling advice that’s been going around for far too long.

To know more about calorie-restrictive diets and how bad they can get, check out my complete article where I compare these diets to intermittent fasting.

13. Fasting With Type 2 Diabetes Is Not Dangerous

I’ll try and be as concise as I can to explain type 2 diabetes.

That’s terrifying, yet genius –

When you’re eating carbs, your body will release insulin. Insulin will then use the carbs for three things, in this order:

  1. To enter mitochondria and burn it up as energy (for the muscles, brain, etc.)
  2. To be stored in glycogen stores in your liver for later use
  3. To be turned into fat and put in your fat cells if the previous both tanks are full

If you’re always eating carbs (I’m speaking about carbs, but sugar, alcohol, smoke, etc. can all affect these processes too), most of the time, your glycogen stores will be full. So a great part of it will be turned into fat.

And you’ll be releasing insulin most of the time since every carb will cause an insulin reaction. Meaning you’ll always have some insulin in your blood. Insulin staying in the blood when you’re not eating is called fasting insulin. Fasting insulin will slowly rise. Your cells will always be exposed to insulin in your bloodstream, causing insulin resistance

It’s like the first time you drank, you got drunk on one beer. 10 years later, you might need 10 or 12 beers to achieve the same effect. With insulin constantly in your bloodstream, you need more and more insulin with each carb you eat, in order to process it, meaning you’ll be left with even more insulin in your bloodstream. This cycle is called the Randle cycle.

Since all your stores are full, all this insulin will turn your carbs, some proteins and even fat (which almost doesn’t raise insulin normally, but since you’ll always have some in your bloodstream it will be too) into fat stores in your fat cells. But your body only has so many fat cells it can fill up.

So, soon enough, your body will take the fat overflows and put it in your abdominal cavity (visceral fat), in your liver (causing fatty liver disease), in your muscles and lastly in the pancreas. The pancreas is responsible for producing insulin, once it’s filled up with fat the beta cells will stop working properly. Those same cells that were pumping lots of insulin.

You might think: yeah, no more insulin, insulin levels will drop then and order will be restored. If you keep eating carbs, it won’t. Without insulin to take care of the carbs, the glucose will end up in your blood causing high blood sugar and eventually death. That’s why diabetic people are prescribed insulin. Which worsens the whole cycle, since insulin resistance and diabetes are caused by too much insulin!

You see there how insulin is the root of all the problems. Do you know what would lower insulin? Restricting carbs and fasting. On a low carb diet, your body won’t raise insulin and without carbs your blood sugar will lower, causing your body to deplete glycogen stores, glycogen in your muscles and then eventually break down fat. Which you weren’t ever able to do with all that insulin floating around since then. Breaking fat down will help clear fat overflow outside fat stores, reduce insulin levels and therefore insulin resistance.

To conclude, fasting is the best way to lower insulin levels and to create the same reaction. So, no, fasting won’t kill you if you’ve got type 2 diabetes, it could even be a way to reverse it. If you’re doubtful about this, I advise reading Dr. Jason Fung The Diabetes Code on the subject.

14. Anyone Can Fast

Okay, if you’ve reached this moment in the conversation where the person in front of you seems to understand what you’re saying, sees the logic behind all your explanations, you’ll certainly get this answer.

I certainly got it from my girlfriend two years ago. She was constantly hungry upon waking up and she thought she was going to collapse if she didn’t eat in the following hour. I still don’t really know what convinced her, but she tried to start intermittent fasting anyway. After only a week, she was able to do an 18 hour fast.

She did it gradually, the first day was maybe 12 hours, then 13, then 12 again, then 15, then 18. And when she discovered it was only a habit she had to get rid of, in about a month, she never had the urge to eat again in the morning.

When we are on vacation, we eat breakfast (hell, we’re on holiday), but most of the time it’s enough to fill us up for the day. And eating a lot of carbs every day, we feel bloated, we spend twice the time in the bathroom, etc. Then going back to intermittent fasting is a real treat!

So, now, she’s the one telling the person in front of us: you can do it. Everybody can do it. It’s in your head. It’s 50 years of wrong education. It’s a whole life of bad habits and addiction you need to shake off, but it will happen quicker than you think!


This was a rather long post. Longer than I expected. Some of these myths would need a whole article, even a book, to be debunked correctly, so no wonder this took some time to explain.

What I really want with this article is:

  • If you’re a skeptic, I hope it’ll make you look deeper into fasting and low carb
  • If you’re already convinced, it might give some strength and arguments to convince other people that fasting and low carb is great

So, I hope this will come in handy to you or anyone else. I have to admit, writing this article made me go so far on certain subjects I actually learned some stuff more precisely.

Explaining things to people truly is a great way to learn!

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