How Long Does the Keto Flu Last?

author avatar Dr. Eric Berg 08/31/2023

If you recently started your keto journey, you may feel unwell, similar to having the flu. Experiencing these flu-like symptoms (the “keto flu”) is nothing to be concerned about—it can actually be a sign your body is adapting to ketosis.

Transitioning your body to burn fat instead of carbs for energy requires significant changes in your metabolic state. As your body adapts, the keto flu will go away on its own.

Let’s talk about how long the keto flu lasts and how you can reduce the symptoms fast.

Woman with keto flu symptoms

How long does keto flu last?

If you just started keto and suffer symptoms of keto flu, you may be wondering how long they will last. The good news is that as your body adjusts, symptoms typically disappear within the first week or two.

Keto flu is temporary. Some people experience only mild symptoms, and others have a strong case of the keto flu. Understanding what causes keto flu and how to tweak your ketogenic diet helps to improve symptoms and lets you enjoy the health benefits of keto faster.   

What is keto?

Keto is a high-fat, moderate-protein, and low-carb diet that switches your metabolism from burning sugar to burning fat.

As you break down fat, your liver creates ketones, a type of acid. Ketones enter your circulation to fuel your body—this state is known as ketosis.

Your body only makes ketones when sugar is in short supply, so you have to limit your daily carbs to 20 to 50 grams.

Keto is incredible for your health. You have more energy and improved cognitive function as a result of the increase in your metabolic rate. In fact, research shows that keto is one of the most effective ways to lose weight fast.

Keto flu symptoms

Your risk of keto flu symptoms depends on your metabolic flexibility. Your age, genetics, current body weight, and lifestyle habits influence how quickly your metabolism can shift into fat-burning mode.

Keto flu symptoms can vary, but the most common symptoms are:

  • Body aches

  • Muscle weakness

  • Brain fog

  • Fatigue

  • Headaches

  • Muscle cramping 

  • Insomnia

  • Irritability

  • Muscle soreness

  • Nausea

  • Sugar cravings 

What causes the keto flu?

Symptoms of the keto flu can feel similar to an infection, but there is no need to be concerned. Experiencing keto flu is a result of the powerful changes in your metabolism in response to lowering your carb intake while increasing your fat intake. 

Here are some reasons why you may experience symptoms of the keto flu.

Dehydration and electrolyte loss 

As your body transitions to keto’s high-fat, low-carb protocol, your insulin levels drop. Insulin is a crucial metabolic hormone responsible for blood sugar regulation and fat storage. 

Low insulin triggers ketosis but also causes water loss and electrolyte depletion in the early days of keto-adaptation. This rapid water loss is commonly observed as quick weight loss but also leads to muscle cramps, headaches, and fatigue. 

Increased B vitamin requirements 

Using fat as a fuel source requires different metabolic pathways than burning sugar. Efficient ketosis relies on good levels of B vitamins

Switching to keto can cause a dip in your B vitamin levels, resulting in typical keto flu symptoms like body aches, low energy, and sugar cravings.    

Metabolic changes 

It’s important to understand that adapting to ketosis takes time. Your body likely has been burning sugar as fuel for years or even decades, and your cells and organs must slowly adapt to fat as the primary fuel. Brain fog and body aches are hallmarks of this transition. 

Carbohydrate withdrawal  

Starting keto can cause carb withdrawal and may make your keto flu symptoms worse. When burning sugar for energy, your brain is primed to seek out more carbs whenever blood sugar is low. 

The transition to a low-carb diet can cause intense sugar cravings, irritability, and lightheadedness.

How to get rid of the keto flu fast

Don’t feel discouraged if you are suffering from keto flu. As your body adapts to the keto diet, this miserable feeling will diminish, and there are plenty of steps you can take in the meantime to reduce symptoms.

Stay hydrated and replenish electrolytes 

As your body adapts to keto, you lose water and essential electrolytes like potassium, sodium, calcium, and magnesium. Replacing electrolytes is vital to fight keto flu symptoms

Bone broth is keto-approved and naturally high in electrolytes. Bone broth also stimulates bile production, supporting fat digestion and absorption. 

Alternatively, find a good quality electrolyte product. Choose a keto-friendly option without added sugars or dextrose. 


Because dehydration can worsen keto flu symptoms, you should drink plenty of water. Increased water loss in the early stages of keto-adaptation means you have to compensate and increase your water intake.

Eat more fat and calories 

Transitioning to keto generally requires significant changes in your diet. You suddenly have a very low carbohydrate intake which can cause intense carb cravings. Ensure that you eat enough fat and calories to curb cravings and hunger

Listen to your body and adjust your meal plan if needed. Some people find it easy to become fat-adapted, and others may need a slower transition, gradually increasing quantities of healthy fat.   

Eat nutrient-dense, high-quality foods 

A healthy and balanced ketogenic diet doesn’t just require low-carb and high-fat foods. The best foods for the keto flu are nutrient-dense foods that support healthy vitamin and mineral levels.

B vitamins are essential for fat-burning—so not including enough vitamin B-rich foods in your diet can worsen your keto flu symptoms and slow keto-adaptation.

It’s important to do a Healthy Keto® diet instead of dirty keto. Healthy Keto replenishes vitamins and minerals by including plenty of green leafy vegetables, avocado, nuts and seeds, pork, seafood, and full-fat dairy.

Get plenty of sleep

It’s not uncommon to experience sleep issues during the early stages of keto. This isn’t anything to be concerned about, and your sleep quality will improve as your body adjusts to keto. 

Good sleep hygiene and a bedtime routine can help you overcome sleep-related symptoms when transitioning into ketosis.

Adjust your exercise routine

It takes your body a while to become efficient at burning fat. Until you are fully keto-adapted, you want to avoid high-intensity exercise to minimize fatigue and muscle pains

Walking, swimming, and weight lifting are good choices during the early phases of your keto diet. 

Key takeaways

Going keto means your metabolism undergoes significant changes, and you may suffer some keto flu symptoms along the way. The good news is that these temporary symptoms will disappear once your body adjusts to this low-carbohydrate diet. 

Pay attention to your body and tweak your keto plan if necessary. Include electrolytes, stay hydrated and eat plenty of nutritious keto-friendly foods. Allow your body to rest and modify your exercise routine until your body is fat adapted.


1. What does the keto flu feel like?

Muscle aches, fatigue, brain fog, and headaches are common flu-like symptoms during the early stages of keto. According to this study, most people describe symptoms of the keto flu to be similar to an infection like the flu.

2. How long does it take for the keto flu to go away?

For many people, keto flu symptoms disappear within the first week or two, but it can take a little longer. How quickly your body adjusts to the keto diet depends on how metabolically flexible you are, your previous dietary habits, and the nutrient density of your meals.

3. Does the keto flu mean it's working?

Yes, keto flu symptoms can indicate that your metabolism is shifting from burning sugar to using fat for energy. This switch triggers changes in your hormones, electrolyte levels, and vitamin requirements.

4. What helps with keto flu?

Pay attention to your body and tweak your ketogenic diet if necessary. Include electrolytes, stay hydrated and eat plenty of nutritious foods high in B vitamins. Leafy green vegetables, avocado, nuts and seeds, pork, seafood, and full-fat dairy are all excellent choices to include in your keto diet. 

5. What is the fastest way to get rid of the keto flu?

Adding electrolytes and staying hydrated are the two most important steps to get rid of the keto flu. Bone broth and electrolyte powder are excellent for replenishing your electrolytes and hydration.

6. How do you prevent the keto flu?

Transitioning slowly into keto, eating plenty of nutritious keto-friendly foods, and getting optimal hydration will support your body in adapting to keto with minimal symptoms.

7. How long does it take for keto flu symptoms to start?

Most people experience some keto flu symptoms within the first week of keto. 

8. What are the first signs of ketosis?

Water loss and increased urination are often the first signs of your body transitioning into ketosis. You may also experience fatigue and cravings as you adjust to the low-carb diet. As you eat more fat and ketone levels rise, your metabolism changes, and you may find that your breath has a fruity smell. Your breath will return to normal once you are fully adapted to keto. 

9. Does everyone on keto get the keto flu?

Not everyone experiences the keto flu, but most people develop some symptoms. Your age, genetics, current body weight, and lifestyle habits are all factors that determine if you develop keto flu symptoms. 

10. What happens during the first week of keto?

During the first week of keto, your body isn't very efficient in burning fat yet. As you drastically reduce dietary carbohydrates, your body burns small amounts of stored sugars for energy, causing water loss and electrolyte imbalances. Because your insulin levels drop in response to the low-carb diet, your body switches to burning fat and producing ketones to fuel your body. With each day that passes, your body will become more adapted to burn fat for energy.

11. Do you get keto flu before ketosis?

Keto flu symptoms can happen while your metabolism switches to ketosis. Once your body becomes fully keto-adapted, symptoms will diminish.

12. How do you feel when you start ketosis?

As your body switches from burning sugars to using fat for energy, you may feel tired and exhausted. Cravings, lightheadedness, brain fog, and muscle pain are all common symptoms caused by the shift in your metabolism during the first few weeks of keto. 

13. Can you get keto flu on day two?

Yes, you can experience keto flu symptoms as soon as your second day on keto.

14. How long does keto fatigue last?

Keto fatigue and exhaustion are common keto flu side effects that commonly last one to two weeks, but they may last longer for some people.

15. What are the symptoms of carb withdrawal?

Most people experience carb flu when starting the ketogenic diet. Cravings, fatigue, feeling jittery, lightheadedness, and irritability are common carb withdrawal symptoms. Eat plenty of nutritious keto-friendly foods to curb cravings as you transition away from a high-carb diet.

16. Can you get a fever as a keto flu symptom?

No, fever isn’t a keto flu symptom. Despite its name, keto flu isn't an infection and doesn't trigger an immune response or a rise in your body temperature.

17. Should I stop keto if I get the keto flu?

No, it's not necessary to stop keto. Having keto flu symptoms means it's working, and your body is transitioning into ketosis. Take steps to reduce symptoms by including electrolytes, staying hydrated, and adding nutritious foods high in B vitamins to your meal plan. Get adequate rest and adjust your exercise routine until you are fully keto-adapted. 

18. Are chills a symptom of keto flu?

No, chills are not a common symptom of the keto flu. Chills and fever happen in response to an infection and result from your immune system fighting a virus or bacteria. 

19. Is brain fog a symptom of ketosis?

Yes, brain fog is a prevalent symptom of ketosis, particularly during the early stages of the ketogenic diet. As your body slowly switches to burning fat instead of carbs for energy, your brain has to adapt to using ketones as an alternative energy source. This temporary brain fog will diminish once you are fully keto-adapted. 

20. How long does keto fog last?

Most people find that keto fog lasts no longer than a week or two. However, keto fog can last longer depending on your metabolism and lifestyle habits. Staying hydrated, replacing lost electrolytes, and eating plenty of healthy keto-friendly foods help you shake the keto fog. 

21. How long does it take the brain to adapt to keto?

It takes the brain between one and two weeks to adapt to keto. 

22. Do you feel better after the keto flu?

You will feel much better when your body fully transitions into ketosis. Once you are fat-adapted, you will start experiencing keto's health benefits, including weight loss, better energy, and improved moods.

23. Does Healthy Keto help prevent the keto flu?

Yes! Healthy Keto is an excellent choice to prevent keto flu symptoms. Healthy Keto focuses on high-quality, nutritious keto foods. Your body will get plenty of B vitamins, electrolytes, and fiber necessary to curb keto flu symptoms like fatigue, brain fog, cravings, and muscle cramps.

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