Written by: Suzie Walker



Time to read 11 min

You're about to start the keto diet, and your keto-following friends keep talking about the Keto Flu.

You may be asking yourself ‘What is the Keto Flu?’, or, ‘Should I worry about the Symptoms of Keto Flu?’

We can help you out with this.

In this article, we'll delve into the cause of the keto flu, ways to reduce keto flu symptoms, and strategies for those out there already struggling with the keto flu.

Let's get to it!

keto flu feeling down

What Exactly is the Keto Flu?

Keto Flu is that icky feeling you may get when beginning a keto diet.

When following the typical high-carb diet that most of the Western world does, carbs are the primary source of energy for your body.

So, when you suddenly cut carbs out of your diet and replace them with high quantities of fats and moderate proteins, your body needs time to adjust to its new source of fuel, ketones. 

When your body switches over to using ketones for fuel rather than glucose, you enter the state of ketosis!

This can cause the keto follower to experience symptoms similar to the common flu, hence the same!

And yeah, we get it! No one wants to suffer from the keto flu, but it shouldn't stop you from at least trying the keto diet. 

While keto flu might make you think twice before starting a ketogenic diet, remember symptoms typically are temporary.

The duration that the symptoms may hang around varies from person to person; you could experience these keto flu-like symptoms for a few days up or last up to a month. The intensity also differs based on various factors such as genetics and how drastically you've reduced your carb intake while adapting to the ketogenic diet.

If you are one of the lucky ones, you may avoid it altogether!

running on empty keto flu

What Causes the Keto Flu?

So what causes the keto flu?

As your body shifts from burning glucose for energy to burning fat (the metabolic state of ketosis), it can take some time to adapt. When you drastically reduce your carb intake, your body gets a bit of a shock. 

This significant dietary shift can cause temporary discomfort and flu-like symptoms. This adaptation period might bring along certain unpleasant symptoms commonly referred to as 'keto flu'.

Also, as you cut carbs out of your diet, your insulin levels drop and your kidneys start shedding excess sodium from your body. While this sounds beneficial (and generally is) it also results in an electrolyte imbalance because our bodies need some sodium for optimal function. That imbalance often contributes to many of the unpleasant symptoms associated with the keto flu.

Factors such as genetics or even previous exposure to a low-carb lifestyle may influence whether or not someone experiences these symptoms.

feeling overwhelmed on keto flu

Signs and Symptoms of the Keto Flu

Now we know why we experience keto flu on the keto diet, let's talk about what the symptoms are:

Fatigue and Low Energy Levels

One of the most prevalent is fatigue or low energy levels. As your body switches its fuel source from glucose (from carbs) to ketones (from fat), you might find yourself feeling more tired than usual. This is a normal part of the transition and should pass once your body fully adapts.

keto flu cramps

Muscle Cramps or Soreness

You might also experience muscle cramps or soreness. Just like with headaches, these can stem from electrolyte imbalances but also result from your body adapting to using different metabolic pathways for energy production.


Headaches are another common symptom reported by those starting on a ketogenic diet. This can be due in part to dehydration or electrolyte imbalances caused by rapid water loss during the first few days of carb restriction.

keto flu mood swings

Tummy Trouble

Digestive issues such as constipation or diarrhoea are other flu-like symptoms that some people encounter when transitioning into ketosis. Changes in dietary fibre and fluid intake combined with shifts in gut bacteria composition could contribute here.

Keto Night Sweats

Does keto make you sweat at night? Well, early in your keto journey you may be one of the unfortunate ones that have to deal with the dreaded night sweats on keto. 

Night sweats are common in the first few days. This is related to the change in water retention, and increased energy levels when reaching ketosis. You may find yourself tossing and turning during the first night of keto, and you may be shocked about the amount of energy you suddenly have, even at 3am!

Keto Hot Flashes

Like Keto night sweats, but during the day! Keto Hot flashes can hit at any time, and may make you feel a little red in the face or sweaty palmed. This is just your body adjusting to a new W.O.E (Way of Eating), and should pass in a few days. 

Mood Swings & Irritability

Finally, mood swings or irritability might surface during this period as well. This could be attributed not only to physical discomfort but also psychological factors such as cravings for carbohydrates that you're now limiting significantly.

Do these symptoms sound familiar? Yes, they're similar to regular flu symptoms. Hence the name!

How to Get Rid of the Keto Flu Symptoms

Now you know why we get these side effects of the keto diet, and what they are, you may be wondering 'How Do You Prevent The Keto Flu?'

Truth is, a full remedy to the Keto Flu may not be completely possible, as most people describe flu-like symptoms associated with the ketogenic diet in the early stages.

While keto flu remedies don't really exist, there are strategies you can implement to alleviate or lessen these symptoms when you start a keto diet:

    Stay Hydrated    

It's crucial for you to drink plenty of water on the ketogenic diet, as staying hydrated can help alleviate some symptoms of the keto flu like headaches and fatigue. When transitioning into a state of ketosis, your body tends to shed excess water and salts. This loss of fluids can lead to dehydration, which in turn triggers symptoms like fatigue and dizziness.

Maintaining proper hydration isn't just good practice and is essential during your keto transition phase. Aim for 2-3 litres of water a day as a starting point; increase this amount if you're feeling thirsty or experiencing dry mouth.

Combating the keto flu is about more than just reducing carbs, it's also about supporting your body through this dietary change by ensuring it has enough fluids.

Not drinking enough fluids may make keto flu worse. And be aware also that some popular drinks are diuretics (Coffee anyone), so go easy on them!

hydration on the keto diet

    Avoid Strenuous Exercise    

While you're adjusting to your new low-carb lifestyle, you might want to take it easy on the exercise front. Heavy physical activity can exacerbate the symptoms of the keto flu as your body is still getting used to its new fuel source.

You don't need to do everything at once. Take one step at a time, especially if you are starting a new lifestyle.

This doesn't mean you should completely abandon all movement; gentle activities such as walking or yoga can still be beneficial and won't put too much strain on your system. 

Just remember, now isn't the time to push for personal bests! No deadlifting or squatting!

Once your body has adapted and the keto flu has passed, feel free to gradually reintroduce more strenuous exercises into your routine.

    Replace Electrolytes    

You need to replace the electrolytes lost due to a low-carb diet. It's uber important!

Keto flu symptoms like fatigue and headaches can be brought on by an imbalance in your body's electrolyte levels. It's common for those starting the ketogenic diet to experience these symptoms as their bodies adjust.

To ease this transition, focus on replacing electrolytes like sodium, potassium, and magnesium by consuming foods rich in these nutrients or consider taking supplements.

Don't hold back on salt! It's a massive mistake when following a keto meal plan. Salt is needed by your body, especially during keto.

A typical sea salt will do you. There's no need to get any of that fancy Pink Hilamayan stuff, its benefits are way overstated!

Replenishing your body with essential minerals will make your journey into ketosis smoother and less discomforting.

electrolytes on keto

    Slow Your Transition Into Keto  

Feeling overwhelmed by the sudden dietary change?

Then slow down!

The goal of the keto diet isn't to make you stressed and miserable!

You can always opt for a slower transition into a low-carb, high-fat diet. Instead of diving headfirst into the ketogenic lifestyle, consider gradually reducing your carb intake. This method can help lessen the shock to your system and potentially alleviate some keto flu symptoms.

By implementing a slower transition to keto, you're giving your body more time to adapt. Begin by slightly decreasing carbs each week while simultaneously increasing healthy fats.

Patience is key during this process, it will take longer to reach ketosis, but the journey will likely be less taxing on your body.

Results will also be slower, however, and you won't hit ketosis until your carbs are low enough! So be aware of that.

    Get Adequate Sleep    

Ensuring you're catching enough Z's can be a real game-changer when your body is working hard to adapt to a new way of eating.

One vital step in managing these troublesome symptoms is making sure you get adequate sleep each night.

Sleep not only helps your body recover and repair but also aids in regulating mood swings often associated with the keto flu. Anyone would feel cranky after only a few hours of crappy sleep!

If you're experiencing the keto flu, being well-rested could make all the difference between having an irritable day and one where you can manage discomfort like a keto champ.

So, prioritise good sleep hygiene, it's a crucial part of transitioning smoothly into ketosis.

sleep hygeine and keto flu

    Stay Busy!    

When you're battling those pesky carb cravings and fighting off fatigue, it's essential to keep your mind occupied and stay busy.

Staying active can be an effective way to manage what's the keto flu.

The more idle time you have, the more likely you are to dwell on the discomfort that comes with transitioning to a ketogenic diet.

The key here isn't physical activity. Remember, strenuous exercise isn't recommended when the keto flu comes knocking—but rather engaging in activities that demand your attention and focus.

Whether it's reading a book, doing a puzzle, or diving into a project at work or home, staying mentally occupied can help distract from any unpleasant symptoms and make your transition into ketosis smoother.

So remember, keep busy and keep your mind off your discomfort!

    Stay Cool    

After securing a good night's rest to manage fatigue and irritability, there's more you can do to combat the keto flu...

Stay cool, literally.

Lower the severity of the keto flu, by using fans or air conditioning if possible. or consider taking cold showers to help regulate your body temperature.

Keep your bedroom window cracked open on a night time, and consider using a lighter blanket while sleeping. Keto night sweats and hot flashes are no joke, prepare for them.

Remember that these are only temporary measures as your body adjusts itself into ketosis, they won't cure the keto flu but will definitely ease some discomforts while transitioning through it.

staying cool on keto

    Make Sure You are Eating Enough Fat (and Carbs)    

While keeping yourself busy can be a helpful distraction from any discomfort of the keto flu, your diet plays a crucial role in managing its symptoms.

As you're following the keto diet, make sure you're eating enough fat—and carbs too.

Yes, even though the ketogenic diet emphasizes high-fat and low-carb intake, it's important to not completely eliminate carbohydrates from your meals.

Just make sure you are cramming your diet with carbs from green vegetables as a priority. They're loaded with electrolytes which will help your symptoms and will keep your net carbs low enough to maintain ketosis.

And it goes without saying that it's important to keep your fat intake at around 70 to 75% of your daily calorific intake. Ensuring that you consume adequate fat is super vital for fueling your body after it adapts to having no carbs. Use a keto macro calculator to understand your own requirements.

how long will keto flu last

How Long Does the Keto Flu Last?

You might feel like you've caught the actual flu for several days or even up to a month as your body adjusts to the ketogenic diet.

The duration of your bout with the keto flu primarily depends on how quickly your body adapts to this new way of eating.

When asking your fellow keto dieters 'How long does the keto flu last?', be prepared for some vastly different answers. There isn't a one-size-fits-all answer. For some people, it may go by so quickly that they don't even notice it, others will feel like staying in bed until early afternoon.

The severity and duration of your keto flu can also depend on genetic makeup and overall health status.

If you were previously consuming high amounts of carbs and suddenly cut them out completely, chances are your body will be shocked by the sudden change in dietary direction. Going from the typical Western diet to keto is quite the opposite.

Remember that though unpleasant, these symptoms actually indicate that your body is transitioning into ketosis, and that is where you want to be!

Don't see keto flu as a negative, see it as a step toward you reaching your goals!

Finally... On the Keto Flu

So, 'What's the keto flu?' Well, now you know!

The keto flu is a collection of symptoms experienced when first starting a ketogenic diet. These can include headaches, night sweats, hot flashes, fatigue, muscle soreness, nausea, and irritability. Known as the 'keto flu', these symptoms are typically short-lived and are simply your body adjusting to a drastic change in diet.

Symptoms can feel similar to the flu and vary from person to person. Each person's experience with the keto flu varies. Some may feel only slightly off their game for a day or two while others might be down for up to a week. The duration and severity depend on several factors including how drastically you cut carbs from your diet, your individual genetic makeup, and overall health.

Drinking enough water can help reduce symptoms and prevent dehydration. Replacing electrolytes through diet can help reduce symptoms, as dehydration can exacerbate things. Consuming foods rich in electrolytes (like avocados or leafy greens), getting plenty of rest, and slowly easing into carbohydrate restriction rather than going cold turkey can also make this transition smoother.

Remember that experiencing the keto flu doesn't mean you're doing anything wrong – it's just part of some people's process of transitioning from glucose-burning to fat burning.

Stick with it!

If you want the benefits of the ketogenic diet, then you may not be able to avoid the keto flu. But the symptoms usually subside in no time, leaving you in the fat-shredding state of ketosis.

What is Keto Flu? Nothing to worry about!

Suzie Walker - Keto Collective


Keto Collective Co-Founder & Naturopathic Nutritionist dipNT.CNM 

Suzie has researched and reviewed the many health benefits of low-carb living. She co-founded The Keto Collective, a company that aims to make it easier to find whole food, great tasting, keto alternatives to their everyday favourites.

Read more about Suzie Walker