The Keto Flu: Symptoms, duration and what to do about it

You started applying the ketogenic diet a few days ago and somehow it didn’t work as you desired.

Instead of all the benefits of ketosis you’ve heard of — better fat burning, more energy, better concentration —, you sit tired and a bit confused at the breakfast table.

Who is to blame for this situation? Ah, yes… The Keto flu! A perfectly normal reaction of your body to switching from sugar to fatty acids as the primary source of energy. Because in order to completely change your metabolism, you first have to make some important modifications.

Now you know that this is one of the usual symptoms of the ketogenic diet. How long does a keto flu last? What are the symptoms? How can I get to grips with these symptoms? And why do I feel so tired?

All these questions and more will be answered in the course of this article. Learn everything you need to know about Keto Flu to get through this section of ketosis as quickly as possible.

What is Keto flu?

The Keto flu consists of a number of symptoms people feel when they start the ketogenic diet for the first time. Keto flu is also one of the first signs of ketosis.

These symptoms are very similar to those of flu and they arise because the body has to adapt to the new diet with a very small amount of carbohydrates first.

By reducing carbohydrates, you force your body to use fatty acids and ketone bodies instead of sugars and carbohydrates to generate energy.

Ketones (ketone bodies) are a byproduct when fats are used by your body as a primary source of energy.

Usually, fat is used as a secondary energy source to bridge times when your body does not have access to sufficient carbohydrates and glucose.

The conscious shift towards the use of fats as a primary energy source is called ketosis. Your body gets into ketosis when you are ready to go hungry or if you consciously give up a large part of the carbohydrates and reduce your daily consumption to less than 50 grams [1].

Your body responds to the reduction of carbohydrates in your diet with withdrawal symptoms. After all, he has been given carbohydrates every day for the last few years. He has now become accustomed to that.

The good news is: The state of Keto flu is temporary! So that we can take a closer look at what you can do about the keto flu, you should first understand why your body reacts with such unpleasant symptoms in the first place.

Why do you get the keto flu?

The symptoms of keto flu are associated with the body’s conversion in relation to the way it can extract energy from your food and the nutrients it contains.

Normally, carbohydrates provide your body with energy in the form of glucose. However, when he no longer gets carbohydrates, he burns ketones and fatty acids instead of glucose to gain energy.

This process can take a few days and especially people who have consumed many simple carbohydrates in the form of pasta, sugary cereal flakes or soft drinks such as Coca-Cola or Fanta before changing their diet will experience more intense symptoms.

That’s sometimes why some people don’t get keto flu at all. These individuals have mostly consumed carbohydrates and sugars in manageable amounts even before the changeover.

There is also evidence that genetics, electrolyte balance and dehydration can affect the strength and expression of the symptoms that follow.

Symptoms of Keto Flu

As soon as you change your eating habits and eat few to no more carbohydrates as part of the ketogenic diet, your body needs some time to adapt to them.

For some people, this period of changeover can be worse than for others. You will notice relatively quickly which group you will belong to.

The first symptoms of keto flu usually appear three to five days after the dietary change. The intensity of the symptoms varies from person to person.

While some individuals make the switch to ketogenic diets without any problems, most people experience one or more of the following symptoms of keto flu:

  • Fatigue
  • Dizziness
  • Abdominal pain
  • Muscle exhaustion
  • Sleep problems
  • Headache
  • Mild nausea
  • Sugar cravings
  • Reduced ability to concentrate

These symptoms can be felt primarily when you have only just started with the ketogenic diet. Symptoms usually last a maximum of one week. However, this time can vary from person to person.

To make sure you can attribute these symptoms to ketosis rather than normal flu, it makes sense to measure your ketone levels with appropriate devices to ensure if you are already in ketosis.

Many beginners who start the ketogenic diet are discouraged by these initial symptoms. However, there are a number of ways to alleviate these symptoms and speed up the onset of ketosis.

What can be actively done about the symptoms?

When you have the Keto flu, you feel miserable. Fortunately, there are a number of effective and practically tested ways to get to grips with the symptoms of Keto flu.

Eating enough fats

As you transition to a ketogenic diet, you’ll notice that in the meantime you’ll have incredibly strong cravings on biscuits, bread or pasta.

You can get to grips with these cravings by simply eating more fats. This is due to the fact that your body now uses fat as an alternative source of energy to carbohydrates. He just doesn’t really know yet and continues to signal to you that he wants carbs.

Therefore, you have to outsmart it and direct your cravings to carbohydrates in the direction of high-quality fats. Even science shows that this trick works in practice and that an increased consumption of high-quality fats (e.g. MCT oil) also reduces the cravings to sugar [3].

If you doubt which foods meet these criteria, here are the 15 best foods for the ketogenic diet.

What you can additionally try to reduce the intensity of the symptoms of keto flu is to reduce the number of carbohydrates slowly and not from one day to tomorrow. For example, you can start removing carbohydrates from your breakfast in the first step. A good alternative to a high-carbohydrate breakfast, for example, is Bulletproof Coffee.

At the same time, you should increase the number of proteins and fats in your diet. This gives your body more time to transition.

Drinking a lot of water

Drinking plenty of water is essential to your health and performance anyway.

Since a ketogenic diet can cause your body to drain heavily at the beginning of the transition, this also increases the risk of your dehydrating [4].

This is due to the fact that glycogen, the stored form of carbohydrates, binds to water molecules. Reducing the number of carbohydrates in your diet will also reduce the amount of glycogen in your body. The glycogen also excreted the water bound to it [5].

Therefore, by drinking exceeds you, you can counteract symptoms such as muscle weakness, headaches or fatigue [6].

Avoid intense workouts

While intense exercise can help you improve your health and get into ketosis faster, it can also make the intensity and strength of symptoms of a keto flu worse.

Fatigue, mild muscle spasms and minimal abdominal pain are common symptoms that you will experience in the first week after your diet change. It makes sense to give your body a little break at this time.

Therefore, you should avoid strenuous workouts and focus instead on less intense activities such as light cycling, walking or yoga.

Sleep enough

Fatigue, mild confusion and dizziness are symptoms you will experience over the course of a classic keto flu.

Lack of sleep and sleep problems also cause your body to release the stress hormone cortisol. This can have a negative impact on the strength of the symptoms as well as your mood and your emotional world [7, 8].

Make sure that you sleep sufficiently, especially during the first four weeks after your dietary change, and actively work on your sleep quality.

If you have trouble falling asleep, you can try one or more of the following sleep hacks:

  • Take less caffeine. Avoid caffeine after 2:00 completely. [9]
  • Take a relaxing bath with lavender oil [10]
  • Get up early and go to bed early. This regulates your sleep rhythm [11]
  • Turn off smartphones or notebooks 30 minutes before bed. Avoid blue and bright light before sleep [12]

Replace missing electrolytes

If you start feeding yourself ketogenic, your insulin levels will inevitably drop a bit. With the decreasing insulin level, your kidney will dissipate excess sodium via your urine from your body [13].

In addition to this effect, the ketogenic diet restricts the consumption of foods that have a high potassium content. These include fruits, beans and starchy vegetables.

However, it is incredibly important to maintain the level of these essential nutrients in your body. Especially in the diet change phase, a lack of electrolytes and important nutrients can worsen the symptoms of keto flu.

By using more salt than usual and integrating green-leaf vegetables and avocados into your diet, you can prevent a deficiency, maintain a healthy electrolyte balance, and reduce some symptoms of Keto flu [14].

How long does a keto flu last?

Fortunately, a normal keto flu lasts only a few days. At most, you will feel the symptoms for an entire week.

In addition, the symptoms appear relatively quickly and then become less bad by the day. With the above tips, you can also help your body with the changeover. This also reduces the duration of Keto flu.

Symptoms of keto flu usually last a few days to a week. However, there are ways to shorten the duration of Keto flu.

The bottom line

The Keto flu refers to a number of symptoms that occur as part of the dietary change towards a ketogenic diet. A keto flu usually lasts a few days to a week.

Symptoms include headaches, fatigue, mild concentration problems and cravings for sugar or carbohydrates.

By eating more fats, drinking a lot of water, not doing intense workouts and getting enough sleep, you can relieve the symptoms of keto flu and reduce the duration.


Fan of everything health and fitness related. My mission is to share my knowledge and experience with as many people as possible and help them to find their ideal path to perfect health.

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