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Home Keto Diet How Long Does Keto Flu Last? Causes, Symptoms, and Remedies

How Long Does Keto Flu Last? Causes, Symptoms, and Remedies

How long does keto flu last

From helping you lose weight to improving cognitive function, there are many reasons why keto is quickly becoming one of the most popular diets in the world. But if you’re thinking about switching to this low-carb way of eating, you may have heard about some concerning side effects, including nausea, fatigue, and irritability.

Collectively, these symptoms are known as the keto flu, and they often cause people to abandon the diet before they’ve experienced any of the benefits. 

While it may be tempting to fall at the first hurdle, it’s important to know that these effects are temporary, and you’ll come out the other side feeling much more energized.

Find out how long it takes to get rid of the keto flu and what you can do to speed up the process.

How Long Does Keto Flu Last?

The symptoms of keto flu generally start to disappear as your body adjusts to this new diet, which usually takes anywhere from a few days to two weeks. It usually takes 10 days for most people to get better.

Whereas some people experience only a mild case of keto flu, others suffer from stronger symptoms, which can last for up to a month in other cases. You should begin feeling better as your body learns how to metabolize and fuel itself with fatty acids more efficiently. 

When does keto flu start? 

Keto flu typically begins within the first 2–7 days after starting the keto diet, with symptoms peaking within the first week. During this time, your body’s carbohydrate stores start to deplete, so instead, it must adapt to using fat as an energy source. 

Most people are able to store around 500 grams of carbs for fuel, so you’ll feel keto flu symptoms when these start to run out.

Although symptoms tend to show up in the first few weeks, in some cases, people may experience them during the first 24 hours of starting the diet. If you don’t feel any flu-like symptoms by the end of the first week, it’s likely that you may not get the keto flu at all.

Factors That Influence the Duration of Keto Flu

As we’ve mentioned, some people’s keto flu symptoms last for longer than others. This depends on different factors, some of which can be controlled and some that are part of our individual genetic makeup, including the following:

#1 Individual adaptation

If you ate a low or moderate amount of carbs before switching to keto, it’s likely that your body may find it easier to use fat as its only fuel source. However, those who ate plenty of pasta, bread, and other high-carb foods may find the transition difficult while their metabolism becomes more fat-adapted.

#2 State of your health

The causes of keto flu are generally unknown. However, those who eat well, exercise regularly, and get plenty of sleep, are likely to respond differently to a sudden change in diet than those who don’t. 

It is because people who are fairly active may already be able to effectively use fat as a fuel source, making the transition to a low-carb diet much easier.

Carbohydrate restriction


#3 Carbohydrate restriction

Although keto requires you to get only 5–10% of your daily calorie intake from carbs, some may find that it suits their lifestyle better to slowly transition to such a low amount. These people are less likely to experience such intense keto flu symptoms as their body gradually adapts to carbohydrate restriction.

#4 Electrolyte balance

How long the keto flu lasts may also depend on the balance of electrolytes within your body before starting the diet. Electrolytes are chemicals like magnesium, potassium, sodium, and calcium that are essential for many processes within the body, from muscle function to hydration.

Any type of low-carbohydrate diet can cause your electrolyte levels to become imbalanced, which can make keto flu symptoms worse, like nausea and cramps.

What Is Keto Flu?

Keto flu, or carb flu as it is sometimes known, describes the flu-like symptoms that you experience after starting a ketogenic diet. This is because the body is trying to adapt to a new low-carb, moderate-protein, higher-fat diet.

Eating in this way allows you to get into ketosis, the process where the body begins burning fat for fuel rather than the glucose it would usually get from food. This causes the liver to produce ketones as an alternative energy source, which requires significant metabolic changes that trigger carbohydrate withdrawal.

Some people may only experience symptoms of the keto flu mildly, which can include keto breath, fatigue, nausea, digestive discomfort, or insomnia, and there are a range of factors that may cause them. 

For example, your vital organs and cells will need to adapt to burning fat for fuel after years of using glucose, which can cause brain fog and aching muscles. Similarly, switching to fat as the body’s primary fuel source relies on B vitamins, leading to a dip in your vitamin B levels. You may therefore experience symptoms such as fatigue and cravings for sugar.

Keto Flu Symptoms

Depending on your age, body weight, lifestyle habits, and genetics, symptoms of the keto flu that you’ll get will vary. However, most people experience some form of keto flu as their body learns how to cope with this major dietary change.

Keto Flu Symptoms

Here are some of the most common signs of keto flu that you’re likely to notice:

  • Fatigue or low energy levels
  • Headache or migraine
  • Brain fog or difficulty concentrating
  • Irritability or mood swings
  • Nausea or digestive discomfort
  • Dizziness or lightheadedness
  • Muscle cramps or weakness
  • Sleep disturbances or insomnia
  • Sugar cravings or increased appetite
  • Cough and sore throat

How to Avoid Keto Flu

To reduce the severity of your symptoms, there are several things that you can integrate into your daily life when just starting out with keto. Find out what they are below:

#1 Gradually reduce carbs

Your brain will continue seeking carbohydrate intake for energy when your blood sugar levels suddenly drop, leading to carb withdrawal symptoms such as sugar cravings and lightheadedness. To prevent these symptoms from being so severe, you should try to gradually reduce the number of carbs in your diet.

#2 Take electrolyte supplements

During ketosis, your insulin levels will drop as your body gets used to the high-fat, low-carbohydrate diet. Insulin is the hormone responsible for blood sugar regulation, and low levels can cause your electrolyte stores to become depleted.

Having an electrolyte imbalance can cause symptoms such as elevated heart rate, nausea, dizziness, and muscle cramps. You can treat this using supplements or keto-friendly drinks that contain electrolytes as a hydration boost.

#3 Include more healthy fats

The ketogenic diet encourages followers to get around 55–60% of their calories from healthy fats. Known as mono or polyunsaturated fats, these are digested slowly and help us feel fuller for longer. You’re, therefore, less likely to get that lightheaded, fatigued, nauseous feeling that comes with hunger.

Plus, these fats come with a whole host of health benefits, and replacing unhealthy saturated fats with them can reduce your risk of developing heart disease, lower inflammation, and support a healthy gut.

#4 Monitor your macros

As previously mentioned, those who previously consumed a carb-heavy diet may experience keto flu symptoms for longer. If you’re unsure of your usual carbohydrate intake, then try using a macronutrient tracking app to record your usual eating patterns.

You can then gradually reduce your carb intake from this number, meaning you’re less likely to encounter symptoms during the transition. 

#5 Drink more water

Along with electrolytes, you’ll also lose more water too as your body adapts to its new food intake. Usually, stored carbohydrates would bind to water in the body, but a reduction in carbs means that this water is now excreted.

Dehydration can increase the effects of keto flu, like fatigue and cramping, so you will need to up your water consumption to compensate. You may also experience diarrhea while starting keto, so it’s important to replace these lost fluids.


How long does keto fatigue last?

Symptoms such as fatigue disappear as your body gets used to your new keto diet, which typically takes between 1 and 2 weeks. However, this may vary from person to person, depending on your previous dietary habits, what you’re eating now, your health, and your body’s ability to adapt.

When is keto flu the worst?

You are likely to experience the worst keto flu symptoms in the first 7 days of transitioning to this diet, and they should disappear after around 2–4 weeks.

Will I feel better after keto flu?

Once your body has fully adapted to using fat for fuel, you should feel much better and begin experiencing the benefits of the keto diet, from helping you lose weight and improving your energy levels to lowering inflammation and preventing brain fog.

A Word From an MD

Although keto prioritizes healthy fats and proteins, you should focus on consuming nutrient-dense foods to support healthy vitamin and mineral levels. This will help to reduce keto flu symptoms, from brain fog to nausea.

For example, as B vitamins are vital for the fat-burning process, not eating enough of them causes your body to take longer to adapt to a ketogenic diet. Try to follow a healthy, clean keto diet by eating plenty of nuts and seeds, avocados, low-carb green vegetables, salmon, tuna, and grass-fed beef.

Unlike influenza, the medically-recognized version of flu, you’re likely to feel well enough to continue with your day-to-day routines. However, the symptoms can be uncomfortable, and so treating your body with kindness is the best way of reducing or preventing them. Be sure to get plenty of sleep and avoid high-intensity exercise until your body adjusts.


Although making the change to a keto diet is beneficial for your long-term health, it can cause you to suffer some flu-like symptoms in the short term. Luckily, keto flu should go away once your body adapts to this new way of eating, leaving you feeling energized and ready to embark on your wellness journey.

If your symptoms continue for longer than expected, you should consult your healthcare professional. The keto diet is unsuitable for those with existing medical conditions, including kidney disease and type 1 diabetes.

Written by
Edibel Quintero, MD

Edibel Quintero is a medical doctor who graduated in 2013 from the University of Zulia and has been working in her profession since then. She specializes in obesity and nutrition, physical rehabilitation, sports massage and post-operative rehabilitation. Edibel's goal is to help people live healthier lives by educating them about food, exercise, mental wellness and other lifestyle choices that can improve their quality of life.

How long does keto flu last

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