Keto flu

The “keto flu” can be unnerving if you don’t understand it.

Without prior knowledge, the symptoms can lead a new keto dieter to believe the diet isn’t working for them. Thankfully, that’s not the case at all!

The keto flu is a natural reaction to entering ketosis, it’s very temporary, and there are ways to remedy it. We’ve included all the details you need to know about the keto flu and what to do if you experience it.

In this article, you’ll learn:

What is the Keto Flu?

Your body burns carbohydrates (glucose) for energy by default.

But when your carb intake is drastically reduced, like on the ketogenic diet, your body is depleted of stored glucose and instead turns to burning fatty acids for energy. This is the metabolic process of ketosis.

The keto flu is a natural reaction to our bodies are entering ketosis and switching to a state of glucose-burning to fat-burning.

Your body’s response to entering ketosis can often mimic symptoms of the flu, thus the name “keto flu.”  

The Common Symptoms of The Keto Flu

Most people experience the keto flu when they first start keto. Here are some of the most frequently reported manifestations of it:

  • Stomach aches or pains
  • Brain fog
  • Dizziness or confusion
  • Nausea
  • Irritability
  • Diarrhea or constipation
  • Muscle cramping or soreness
  • Lack of concentration or focus
  • Trouble falling or staying asleep
  • Sugar cravings
  • Heart palpitations

Keto flu symptoms usually occur within the first day or two of starting a ketogenic diet, and the severity and length of symptoms vary per person. Some people may have no symptoms at all, while others could experience several for up to a week or two.

Either way, the symptoms shouldn’t last more than a couple weeks and should go away once your body is adapted to burning fat for fuel.

What Causes the Keto Flu?

The keto flu is essentially the result of three things:  

  1. Becoming “keto-adapted.”
  2. Electrolyte loss and dehydration.
  3. Withdrawal from carbohydrates and sugary foods.


Our bodies have two primary sources of energy:

  • Glycolysis: converting glucose into energy
  • Beta-oxidation: converting fat into energy

Keto-adaptation means getting the body used to the process of beta-oxidation. This is easier for some bodies than others.

Metabolic flexibility refers to how well a person can adapt to using a different fuel source: switching from burning glucose to burning fats. Those with less metabolic flexibility are more likely to experience keto flu symptoms as the body adjusts[*].

Genetics also play a part. Some people are simply better able to handle the energy switch.

Electrolyte Imbalance

The standard American diet contains a lot of processed foods, which are high in added sugars and salts. When we switch to a keto diet of whole foods, most salt-laden choices are eliminated and sodium intake is drastically reduced.

Sodium causes the body to retain water, so less sodium intake means less water retention. The lack of carbs also lowers insulin levels. All of this leads the kidneys to release excess water[*].

With that excess release of water, electrolytes are flushed out, leading to electrolyte imbalance and dehydration. This can cause flu-like symptoms until everything becomes balanced again.

Carbohydrate Withdrawal

Some research has shown sugar affects the brain in a way similar to heroin or cocaine[*]. It’s pleasurable, and we get a nice shot of the “feel good” hormone, dopamine, when eating sugar.

Plus, the addictive nature of these foods doesn’t help[*].

When sugar is drastically reduced from starting a keto diet, we can experience withdrawal effects like mood swings, irritability, cravings for sugar, and other symptoms of the keto flu.

Someone who has come from eating a diet full of processed and refined carbs and sugars is more likely to also experience these withdrawal-like symptoms and have more trouble adapting to fat burning.

Now that we’ve covered the “whats” and “whys,” let’s talk about how to alleviate these issues.

How to Avoid or Get Rid of the Keto Flu

Although the keto flu is temporary, there are things we can do to reduce or even eliminate symptoms during the transition into ketosis.

Stay Hydrated

The water loss that occurs at the beginning of a ketogenic diet needs to be replenished. This can help reduce keto flu symptoms like headaches, fatigue, or nausea that are often caused by dehydration.

Keep water near you to drink regularly throughout the day. Always drink when you feel thirsty.

If your urine is yellow, you need to drink more water. Clear urine is an indication that you’re well hydrated.

Often thirst is a sign of dehydration already, so try to get ahead of it.

Replenish Electrolytes

As mentioned above, electrolyte imbalances can cause keto flu symptoms. Here are some of the best ways to mitigated this:

Get Plenty of Sleep

Getting at least seven hours of sleep a night is important for anyone, and even more so for the keto dieter.

Your body is experiencing a lot of changes as it switches fuel sources, so getting plenty of sleep can help reduce stress and fatigue.

If you struggle to get enough sleep per night, try incorporating a power nap or two into your day.

Do Light Exercise

Exercise performance may temporarily suffer while the body is adapting to higher fat and low carb intake.

At the same time, getting light exercise 2-3 times per week can help make your body more efficient at switching between carbs and fats for energy[*], helping to decrease keto flu symptoms more quickly.

Increase Fats and Calories

Your body is no longer getting its energy from carbohydrates and sugars, so it needs plenty of fat for fuel. Make sure the calories from carbs are replaced by eating plenty of keto-friendly fats.

Supplement with MCT oil powder to help further increase ketone levels for fuel.

If the keto flu is persisting longer than a week, re-evaluate your macros. You might still be eating too many carbs and not enough healthy fats!

Take Exogenous Ketones

Exogenous ketones are ketone salts you can ingest.

They provide your body with additional ketones to help it become more fat-adapted and enter ketosis more quickly. This can be really helpful in preventing or even eliminating keto flu symptoms.

Be Patient and Take Care of Yourself

Use the healthy tips above to help reduce symptoms and possibly even avoid the keto flu all together. Also keep in mind that the keto flu induction phase is just the beginning, and if you experience it, symptoms will subside; just give them time.

Once the hard part is over, you’ll be reaping the benefits of keto and thanking yourself for staying strong.

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Responses (14)

  1. This was very helpful. I’m experiencing at least half of these symptoms and am really struggling so will incorporate some of your suggested helps.

  2. I’ve been on the keto diet for about 45 days, ad no issues at first but now I am experiencing many of these symptoms. Any ideas on why this is happening?

  3. Been on it for almost a month. I have sour stomach, weakness, sleeping is off, dizziness, light headedness and just feel like crap. Need to exercise but don’t have energy.

  4. I’m only two weeks into it I get to sleep just fine it’s staying asleep what’s hard. I woke up today with no energy and feeling like I had to vomit. I went back to sleep till 3 pm. I hope this goes away fast cause I have work and a family to take care of. I don’t want to cut my self short and cut my self off this diet cause it is working.

  5. Two weeks in and yesterday felt hot and sweaty with tummy pains… diarrhea. Urine test strip was dark purple so lots of ketones in my wee. Feeling hot and sweaty.
    Strangely though feel like my fibromyalgia brain fog has completly lifted and have more energy. Doing intermittent fasting and having two meals in an eight hour window.
    Going to soldier on but cant be too far from the toilet today lol.
    PS….not hungry

  6. The trick to this is not to cut carbs out drastically. Many people go crazy limiting themselves to 20g of carbs when your body is used to hundreds. The key to success is to slowly cut back on carbs until your body reaches 20-25g tolerance.

  7. I have learnt a lot from this explanation. I am feeling some of the symptoms. I have a terrible headache for which I take Tylanol. I hope to get out of this state quickly. Iam seeing results from the low carb diet.

  8. How do I know if I have keto flu or real flu or allergies? The keto test strips say I only have a small number of ketones. So, does that mean I can’t have keto flu? One weird symptom I rarely get with flu or allergies is I am very light-headed when I stand up.

  9. For me it is a little different, I stopped eating Bread, rice last year and ofcourse sugar. Then I stopped most of the potatos and pasta. Maybe on of the once a week. Everything fine! Then last month a tried the 5 day water fast, used some salt every day, Keltic salt. The last day at the end I started to feel like having a flu. Before I started the fast, I have to mention, I was in full Keto. So 2 hours before the 5 days ended, I stoped. It took 16 hours to feel better.
    Last week I have tried again. Now the 3th day I became sick, no power, realy bad. I continu 24- hours, but the I stopt. After now 2 days, slowly I star to feel better. What is the reason for this?? I am still in Ketosis

  10. I’ve only bee doing the Sroldiet for six days. I have lost seven pounds and felt fine until tonight. I woke up aching all over my body feeling cold. I mean really aching! I’ve never had the flu but I imagine it’s like this. I literally lived on sweets and carbs. So I’m sure that’s it. I craved water when I woke up like this and I understand that’s normal. I’m not giving up!

  11. Hi Jel, within the first 2-4 days of beginning a keto diet, a common side effect is known as the “ketosis flu” or “induction flu” because it mimics the symptoms of actual flu. We recommend to stay very hydrated and increase your salt intake. Also be sure you’re eating enough.

  12. Hi Dawn, common symptoms of keto flu are headaches, tiredness or lack of motivation, lethargy, brain fog or confusion and irritability. If you experience this, we recommend to stay very hydrated and increase your salt intake. Also, be sure you’re eating enough.

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