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What Is Keto Flu?

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Ketogenic diet, commonly known as Keto, has become incredibly popular in recent years. It is a high-fat, low-carb diet that promises to help you lose weight and improve your overall health. However, following the Keto diet often leads to a temporary condition called the Keto flu.

Explanation of Keto Diet

The Keto diet is centered around consuming mostly fats, moderate amounts of protein, and very few carbohydrates, putting your body in a metabolic state called ketosis. In this state, your body burns stored fats for energy instead of glucose from carbohydrates.

Brief Description of Keto Flu

Keto flu is a temporary condition that affects people who have recently started following the Keto diet. It is not a real flu but has symptoms similar to the flu. The reason for the symptoms is that the body is making a transition from burning carbs for energy to burning fats. This transition can take a few days to a few weeks, and during this time, the body withdraws from carbs, leading to flu-like symptoms.

What is Keto Flu?

Keto flu is a temporary condition that affects people who have recently started following the Keto diet. It is not a real flu but has symptoms similar to the flu. The reason for the symptoms is that the body is making a transition from burning carbs for energy to burning fats. This transition can take a few days to a few weeks, and during this time, the body withdraws from carbs, leading to flu-like symptoms.

Definition and Causes

Keto flu is a combination of symptoms that occur when you start the Keto diet or go through a period of carbohydrate restriction. The symptoms of Keto flu arise because your body is adapting to the new diet and transitioning to a state of ketosis. During this time, your body may experience a range of symptoms, including:

  • Headaches
  • Fatigue
  • Dizziness
  • Nausea
  • Irritability
  • Muscle soreness and cramps

Keto flu is caused by a change in the types of food you consume, leading to a shift in your body's metabolism. When you consume high levels of carbohydrates, your body burns glucose for energy. However, when you restrict carbohydrates, your body begins to use stored fat as a source of fuel.

Symptoms of Keto Flu

The symptoms of Keto flu vary from person to person. Some people may experience mild symptoms, while others may have more severe symptoms. Common symptoms include:

  • Headaches
  • Dizziness
  • Fatigue or weakness
  • Muscle cramps and soreness
  • Difficulty sleeping
  • Irritability
  • Brain fog or difficulty concentrating
  • Nausea or vomiting
  • Constipation or diarrhea

Timeline and Duration

Keto flu typically occurs within the first few days of starting the Keto diet or after a period of carbohydrate restriction. The symptoms usually last for several days up to several weeks. However, the duration of symptoms varies from person to person, and some people may experience symptoms for a longer period.

Risk Factors

Anyone who starts the Keto diet or restricts carbohydrates is at risk of experiencing Keto flu. However, some people may be more susceptible to symptoms than others. Risk factors for experiencing Keto flu include:

  • Reducing carbohydrate intake abruptly
  • Inadequate hydration
  • Electrolyte imbalances
  • Not eating enough calories and nutrients
  • Underlying health conditions, such as diabetes or thyroid disorders

Prevention and Treatment

Keto flu is a common issue for people following a Keto diet, but there are measures you can take to prevent and treat it. Here are some options:

Prevention Measures

  • Gradual reduction in carbohydrate intake: Reducing the consumption of carbohydrates gradually can help ease the transition into the Keto diet, leading to fewer symptoms of Keto flu.
  • Hydration: Drinking enough water can help prevent dehydration, a common issue in people with Keto flu. As a guideline, aim for 8-10 cups of water per day.
  • Electrolytes: Keto flu symptoms can be alleviated by consuming electrolytes, which help balance minerals in the body. This can be done by adding a pinch of salt to foods or drinking sports drinks that contain electrolytes.
  • Nutrient-rich diet: Eating a diet rich in nutrients, such as leafy greens, nuts, and berries, can help prevent nutrient deficiencies that may exacerbate Keto flu symptoms.

Treatment Options

If you experience symptoms of Keto flu, the following treatment options can help alleviate them:

  1. Dietary Changes: Adjusting your Keto diet can help reduce symptoms of Keto flu. Consider adding more healthy fats, reducing protein intake, and increasing carbohydrate intake slightly can ease the transition process.
  2. Hydration and Electrolytes: As mentioned, staying hydrated and consuming electrolytes can significantly reduce the symptoms of Keto flu. Energy drinks and supplements are available that contain additional electrolytes.
  3. Rest and Sleep: Getting enough rest and sleep can help the body recover and feel better during this transition period. It is advisable to take frequent breaks throughout the day to relax and rest.
  4. Medications: Over-the-counter pain relievers such as ibuprofen, aspirin, and acetaminophen can help relieve headache and other symptoms of Keto flu. For dehydration, an oral rehydration solution (ORS) can be used.

Keto flu is a temporary condition that will subside once your body adjusts to the Keto diet. Be patient and try these suggested remedies to ease your symptoms. Remember that if you have severe symptoms or persistent dehydration, it may be best to contact your doctor for medical attention.

Complications of Keto Flu

While Keto flu is typically a harmless and temporary condition, it can sometimes lead to complications that require medical attention. Here are some of the possible complications:


Dehydration is one of the most common complications associated with Keto flu. As the body adapts to the low-carb, high-fat diet of Keto, it tends to expel more water and electrolytes through urine. This can cause dehydration, with symptoms such as headache, dizziness, and fatigue. Severe dehydration can lead to kidney damage, heat exhaustion, or even heat stroke.

To alleviate dehydration, it's important to drink enough fluids, especially water, and consume enough electrolytes such as sodium, potassium, and magnesium. It is recommended to drink 8-10 cups of water per day and to add a pinch of salt to meals. Energy drinks and supplements can be taken to supplement electrolytes if necessary.

Electrolyte Imbalance

Keto flu can lead to an imbalance of electrolytes in the body. As the body releases water, it also releases important electrolytes such as sodium, potassium, and magnesium. This can lead to a deficiency of these minerals, causing symptoms like muscle spasms or cramps, heart palpitations, and constipation.

To prevent and treat electrolyte imbalances, it is important to consume enough of these minerals in your diet. Foods such as avocados, nuts, leafy greens, and oily fish are rich in electrolytes. Alternatively, supplements can be taken to supplement any deficiencies.

Nutrient Deficiencies

While following the Keto diet, individuals may restrict consumption of certain food groups, such as fruits, starchy vegetables, and whole grains. This can cause nutrient deficiencies and impair your body's ability to function optimally. For example, deficiency in calcium, vitamin D, and magnesium can cause issues such as weakened bones, muscle cramps, and muscle weakness.

To prevent nutrient deficiencies, it is important to consume nutrient-rich foods such as dark, leafy greens, nuts, and berries. Supplements may also be taken to fill any gaps in your diet that may cause nutrient deficiencies.


Keto flu can sometimes lead to various complications that require medical attention. To prevent complications, it is recommended to stay hydrated, get enough electrolytes, and consume a nutrient-rich diet. Any persistent or severe symptoms should be reported to a medical professional for evaluation and treatment.


Keto Flu can be a challenging experience for those adapting to the ketogenic diet. The symptoms can be uncomfortable, and in some cases, debilitating. While these symptoms are temporary, it's important to adopt some simple measures to ease the transition and prevent complications.

Recap of Keto Flu

Keto Flu is a constellation of symptoms that occur as the body adapts to a low-carbohydrate, high-fat diet. Symptoms can range from mild to severe and may include fatigue, headache, irritability, muscle soreness, and nausea. However, these symptoms are generally temporary and tend to dissipate once the body becomes accustomed to burning fat for fuel instead of carbohydrates.

Emphasis on the Importance of Awareness and Seeking Medical Attention

While some may think of Keto flu as a minor inconvenience that one toughs out, it is essential to take it seriously. Individuals transitioning to a keto diet should be aware of the condition and be prepared to take measures to alleviate the symptoms, such as staying hydrated and consuming enough electrolytes.

It is also important to note that while Keto Flu is generally harmless, it can lead to complications in severe cases. If you experience severe or persistent symptoms, it's important to seek medical attention from a qualified healthcare provider. Medical attention may be required if the individual is experiencing chest pain, difficulty breathing, or loss of consciousness.

In conclusion, keto flu is a manageable and temporary condition that one may experience while transitioning to a ketogenic diet. Awareness and precautionary measures can contribute to reducing your risk and increasing your chances of a smoother transition. By seeking medical attention, staying hydrated, monitoring electrolytes, and maintaining a balanced diet, individuals can make the transition to a ketogenic lifestyle as comfortable and safe as possible.

William H. McDaniel, MD

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School.

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