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The Keto Flu, Side Effects, and Remedies

Over the years, we have seen many diets come and go. Some have proved to be fads, some have been quick fixes, some have been absolute nonsense, but some have withstood the test of time and have been found to be beneficial.

Ketogenic diets prioritizing fat as a primary macronutrient, along with moderate amounts of protein and low carb intakes have proved particularly popular lately, which is why keto diets are now all the rage.

Keto diets can indeed promote weight loss, increases in energy, and improved cognitive health and function, but they are not without their drawbacks. One downside of following a ketogenic diet is keto flu, which is what we’re going to be looking at today.

If you’re thinking of going keto and want to understand what carb flu is, you’ve come to the right place. Here’s everything you need to know about Keto Flu. (1)


What is ketosis and why is it important?

Ketosis is a natural process which occurs when the body doesn’t have access to sufficient amounts of carbohydrates to use for fuel.

You see, the body uses carbohydrates as its primary source of energy because it finds them so easy to break down and convert into glucose. When we take away the carbohydrates needed, the body begins to panic as it no longer has access to the ingredients needed to produce fuel.

Eventually, the body looks for other alternative sources of energy, which it gets in the form of ketones. Ketones are enzymes produced in the liver when the body enters a state of ketosis.

Once in ketosis, your body uses ketones as energy instead, which prove useful for energy levels for the body and for the brain. What’s more, in order for the liver to produce these ketone enzymes, it needs fat, not only from the diet, but from the body as well.

This is why the keto diet is high in fat and it is why the keto diet is also so beneficial for people looking to lose weight.

One major downside to keto, though, is the fact that when your body makes the transition over into ketosis, you often feel unwell and can suffer from what is known as keto flu, or carb flu. (2) (3)


What is the keto flu?

Okay, so we know the basics behind ketosis, but now let’s look at the darker side of keto, the dreaded keto flu.

Keto flu is not actually a real influenza virus, and lord knows we’ve all had our fair share of virus-related content as of late. Instead, keto flu is a term used to describe a collection of flu-like symptoms which set in when people are making the transition over into ketosis for the first time.

It is known as ‘carb flu’ or ‘keto flu’ because these symptoms can make people feel very similar to how they feel when they’re suffering with the flu.

The main reason for this is simply due to the fact that the body is forced to adapt to a new source of energy, and for the first few days it simply cannot cope.

Ketones are by-products of the metabolization of fat, which basically means that they are produced when fat has been metabolized within the body.

Incidentally, fat is actually the body’s preferred source of energy, but it’s simply that the body finds it easier to convert carbs into energy than fat, which is why fat is reserved as the secondary source of fuel. Without carbs, fats are forced to step up, as it were.

By removing carbs, this shocks the system and your body almost goes into a state of withdrawal as it craves the carbs it needs to sustain itself. (4


Keto flu symptoms

So, we’ve established what ketosis is and we’ve established what keto flu is, or at least, why we suffer from it. Now, though, we need t take a look at how keto flu can affect you.

Here are some, not all, of the more common symptoms associated with what is known as the keto flu. (5)


One of the most common side effects and symptoms of the carb flu is tiredness.

You’ll notice that, for the first 2 – 5 days of cutting out carbs, your energy levels will plummet. You’ll feel tired and lethargic because your body is in starvation mode and is trying to preserve energy and slow down your metabolism.

Normally we consume anything from 200 – 340g of carbs each day, yet on keto we should aim for around 20 – 50g at the absolute most.

For the first few days of keto you’ll feel tired, you’ll have no energy, and you’ll just want to sleep. If you persevere, though, you’ll find that, once in ketosis, you feel great.


Another common symptom of keto flu is a persistent headache that you just can’t seem to shake, no matter how much water you drink or how many tablets you take.

Experts aren’t quite sure why some people experience headaches as part of keto flu, though some believe that, as the body slows everything down because it thinks it is starving, this includes blood flow and a lack of blood to the brain could be responsible.

Another likely cause is that keto diets can cause you to rapidly shed water weight, which can result in dehydration. A common sign of dehydration is headache.


We won’t get too graphic here, but another common symptom of keto flu is constipation.

Too much protein in the diet can have that affect on the bowels, and as most forms of roughage are fairly high in carbs, we often suffer from a lack of fiber and roughage in our diet.


Again, not going into too much detail, but ironically, as well as constipation, another sign of keto flu is diarrhoea.

Usually, as your body uses up the last remnants of glucose in your system, diarrhoea will follow.

Lack of concentration

Another common symptom of the keto flu is a lack of concentration.

People that are dealing with the keto flu often find that they can’t focus or concentrate for long durations of time. Their reactions and reflexes are also much slower than usual.

Again, once they enter a full state of ketosis, ironically their brains work better than ever and their cognitive health improves. This is largely because the brain finds it particularly easy to utilize ketones as energy.

Hot flushes and dizziness

Much like with the real flu, people often find that they experience hot flushes and dizziness when experiencing the ill-effects of keto flu.

It is not uncommon for people to have to lay down because they feel dizzy, or to wake up in the night covered in sweat.

The good news is that, once the transition over to keto has been made, these symptoms go away.


Finally, the last symptom of keto flu which we’re going to look at today is nausea.

A lack of energy, along with the dizziness that often goes with keto flu means that people trying to follow a ketogenic diet will often feel nauseous and sick thanks to a distinct lack of carbs in their diets.

keto flu remedies

If you stick it out, you’ll find that the symptoms of carb flu such as keto diet stomach pain and nausea, will eventually go away as you make the switch over to using ketones as fuel rather than glucose.

However, that isn’t much help for people who are suffering with the carb flu symptoms worse than others.

If you’re one of these individuals and are looking for a solution, here are some carb flu cure tips and keto flu remedies. (6)


Stay well hydrated with water

One of the best ways of helping to ensure that you don’t succumb to the ill effects of the keto flu is to stay well hydrated by drinking plenty of water.

One of the most common symptoms of keto flu is a headache which is likely caused by dehydration.

Remember, keto diets result in a rapid loss of water weight and the more water we lose, the greater the risk of dehydration.

Replacing this lost fluid by drinking plenty of water is essential. Avoid “diet” sodas as, even though they’re sugar-free, they’re also full of artificial sweeteners which, ironically, can cause headaches as well as other chronic health issues.

Try to avoid intense exercise

Once in ketosis you’ll find that your energy levels have increased dramatically and you’ll actually find it easier than ever to exercise.

However, before that, your energy levels will plummet and you’ll feel lethargic and fatigued. Intense physical exercise could put your body under too much stress because, until in ketosis, you won’t have enough energy.

If you do exercise while transitioning into ketosis, be sure to stick with light intensity exercise to begin with.

Get enough sleep

When you’re dealing with keto flu, your body will be crying out for sleep. You should listen to your body and give it what it wants/needs.

A lack of sleep can make us even more fatigued, plus it can lead to an increase in the production of cortisol. Cortisol is a stress hormone that negatively impacts the body and can exasperate the symptoms of keto flu.

One of the best keto flu remedies is to simply ensure that you are getting enough sleep each night. Ideally you should be getting between 7 and 9 hours, though, again, listen to your body, and if it needs more, give it more.

Get enough fat

The keto diet is a low carb, moderate protein, high fat diet. For people following keto for weight loss purposes, eating fat to lose fat seems counter intuitive at first and people often shy away from fat for fear of gaining weight.

Without fat, your body won’t be getting enough calories/energy, plus the body needs fat to produce ketones. If you are depriving your body of fats it will find it harder to produce the ketone enzymes needed to enter a state of ketosis.

Your fats should primarily come from healthy fat sources such as salmon, mackerel, whole eggs, oily fish, avocados, nuts, seeds, coconut oil, olive oil, and so on.


Gradually reduce your carbs

Some people that are looking to get started with a keto diet will find that it is easier to gradually reduce their carb intakes, rather than dropping them all at once.

Rather than going from, say, 350g of carbs per day to 20g, try to reduce your carb intakes by 100g per day until you’re at around 20g – 50g for the day.

How long does the keto flu last?

To answer how long keto flu lasts would be like answering a question regarding the length of a piece of string.

In truth, there is no one true answer because everybody is different.

Symptoms usually start from the very first day of carbs being drastically reduced, and for some people, the symptoms can last around 3 – 5 days.

Some people experience the keto flu for around 7 days, though some may experience mild symptoms for as many as 10 days.

Does keto flu affect everyone?

One thing that is worth noting, is that keto flu does NOT affect everyone.

Whereas some people cutting carbs out in order to follow keto will suffer with extreme carb flu symptoms, others won’t experience any symptoms at all.

It mainly comes down to genetics, as some people are more sensitive to a lack of carbs than others.

Final thoughts

As you can see, there is a lot of evidence out there regarding keto diets and while they’re not without their risks, many agree that the pros outweigh the cons.

Regarding the cons, though, we can’t talk about keto diets and not talk about keto flu. There’s no denying that the symptoms associated with it are not pleasant, but not everybody is affected and they don’t last forever.

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