The Keto Flu – Symptoms, Side Effects & How to Cure It

Table of contents

The Keto Flu – Symptoms, Side Effects & How to Cure It

If you’ve ever poked around the keto diet or thought about doing a low carb diet – you might have heard of keto flu. It sounds bad – really bad – but is it something you should be worried about? We’ll break down the mystique so you know exactly what to expect

What Is Keto Flu?

Despite it’s name – keto flu is not an actual “sickness” – rather it’s a period of low energy that most keto dieters go through when adapting the keto diet and expanding their metabolism from burning “mostly carbs” to using “ketones” for fuel. Your body has two energy systems and the keto system forces you to to adopt the second, slower burning, more even energy system during ketosis – but the transition can sometimes be bumpy. This transition is what we call “keto flu.”

Keto Flu Symptoms

If you’re worried about hte keto flu, or think you might be going through it right now – here are some of the more common symptoms you can expect to pop up – including:

  • low energy
  • lack of focus
  • nausea
  • diarrhea
  • cramps
  • constiptation
  • poor concentration
  • poor sleep
  • “brain fog”
  • general sense of dread about the world

We’re kidding about the last one, but you can see why people call it the keto flu – it’s not fun!

Why The Keto Flu Happens (the science)

The keto flu happens because you’re moving from a carbohydrate rich environment to a fat-focused diet. When you do this, your body has to adapt by getting energy from ketones rather than carbohydrates.

Long-term, this is great because ketones are slower burning, longer-lasting sources of energy. They can give you sustained energy over hours and often make you feel like you have more energy than ever.

However, when you first start to make the adjustment, your body is not very good at using ketones – so you’re both not getting fuel from carbohydrates and not getting fuel (efficiently yet) from ketones.

This means you’re going to have a lack of energy and usually feel like you’re “dragging.” Not great!

So what should you expect timeline wise and what can you do to mitigate this?

The Keto Flu Timeline

Most people want to know what to expect about the keto flu, so we broke it down to an easy-to-understand timeline.

When Does Keto Flu Hit?

You’ll typically notice the onset of keto flu to happen within 24-72 hours of removing your carbohydrate source. It may hit sooner or later, but usually arrives consistently within 2-7 days of starting keto.

How Long Does Keto Flu Last?

The keto flue can last anywhere from a couple days up until a month. It all depends on how much you’ve experimented with keto before, how adaptable your body is and how well you are implementing some of keto flu cures we’ll talk about below.

Some people see huge changes in their ability to adapt to ketosis with the addition of a simple routine.

The Cure for Keto Flu

Again, keto flu is part of your body’s adaptation process as it becomes more metabolically flexible – being able to slide between burning carbs and burning fat for energy.

Keto flu may go away on it’s own as your body adapts over time, but if you want to help accellerate the process, here are some solid “cures” (your mileage with these may vary).

Drink Water

Stay hydrated. When you go low carb, you may notice that you flush out a bunch of water. This can cause you to be dehydrated without knowing it. Make sure you replenish yourself with plenty of liquids and hydration throughout the day.

Consume some more Salt

If you’re struggling with naseau or cramps – adding salt into your diet can help with these symptoms. Water alone won’t replace many of the nutrients your body needs to adapt – so make sure you’re getting enough electrolytes – and specifically salt!

Our favorite electrolyte supplement is LMNT

Consume More Fat

Often when people cut out carbs, they also cut out calories – don’t do this! You want to become fat adapted – not starve yourself. Try consuming more fat so your body has the proper amount of calories to function and you might be surprised as how much better you feel.


Sleep is when your body recovers the most. Good recovery is going to be the key to making sure your body continues to perform at it’s best.

If you need a good performance focused sleep supplement – we recommend Impossible Sleep.

Take Exogenous ketones

Part of the reason your body is going through a “flu” is it’s sturggling to adapt to using ketones. By supplementing with exogenous ketones – you give your body the ability to ingest the ketones without having to break them down yourself. This helps “bridge” you over until your body is better able to more efficiently extract ketones.

If you need some exogenous ketones – we highly recommend HVMN. They taste bad, but work great.

Best Ketone Drink
H.V.M.N. Health Via Modern Nutrition

Taste bad. Works good. The best exogenous ketones on the market.

We earn a commission if you make a purchase, at no additional cost to you.


Even if the idea of a workout makes you want to lose your lunch, sometimes a decent walk, some time in the sun and some movement is all your body needs in order to “reset” and start feeling better. You don’t have to do a level100 Crossfit metcon – but a little movement might be good for your soul.

How to Avoid Keto Flu in the First Place

The best way to avoid the keto flu is to start the “keto flu cure” methods as soon as you can when starting keto.

  • Drink plenty of water and stay hydrated.
  • Consume electrolytes – especially salt.
  • Consume more fat
  • Try exogenous ketones
  • Get outside and move
  • Make sure you’re sleeping well

FAQs on Keto Flu

Keto Flu Threads on Reddit

We combed reddit for the best keto flu threads – check these three out.

Remember whenever you’re on reddit – that you’re on reddit. While the wisdom of the crowds is often helpful – at some points you can also find the worst take on the internet here.

Does Keto Flu give you diarrhea?

Yes, one of the side effects of keto flu can be diarrhea. If this happens to you, make sure you’re properly hydrating and drinking enough electrolytes.l

Can you get a headache during keto flu?

Yes, in fact, the term “keto headache” is sometimes commonly used instead of “keto flu.”

Do I Have Keto Flu Naseau?

Yes, sometimes one of the primary symptoms people have during keto flu is nasaeu.

Other Articles That Help With Keto Flu

If you’re still looking for more resources on keto, you’re in luck – we’ve got a bunch.

Some Keto Products That Might Help

If you’re trying to avoid the keto flu – check out some of the products below that might help stave off some of the cravings and headaches associated with this keto headache.

Other Great Keto Flu Resources

We spent quite a bit of time researching this article to make it the best on the internet. For other great resources we came across while creating this resource, check out these pieces on the keto flu below:

Picture of Joel Runyon
Joel Runyon
Joel Runyon is the founder of Ultimate Meal Plans. Joel is an ultra endurance athlete and entrepreneur. He's also the founder of Ultimate Paleo Guide, MoveWell and is the founder of IMPOSSIBLE ® - a lifestyle performance brand helping people push their limits in fitness and life.

Disclaimer: This post may contain affiliates links. We may receive a small commission if you use them to make a purchase. The price remains the same to you and the program helps us bring you the best content possible. Read our full disclaimer here.

Try Meal Planning Free for 14 Days