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What is Keto Flu? Symptoms, Causes, Recovery, and More

You may have heard the term ‘keto flu’ recently and wondered why so many people are talking about it. With the keto diet gaining more and more mainstream popularity, people are becoming increasingly curious about the short term side effects associated with starting the diet. 

You can think of the keto flu as essentially a group of flu-like symptoms, that occur as the body adapts to a drastic reduction in carbohydrate consumption. Unlike the actual influenza virus though, there is no vaccine to prevent the keto flu and no medication to hasten recovery. 

But there are definitely ways to lessen the severity and duration of the symptoms. And by being proactive, it may even be possible to avoid it entirely. In this article, we’ll examine what the keto flu is, what causes it, and how to recover from it.

A Brief Summary of The Keto Diet

In order to understand what the keto flu is, you need to have basic knowledge of the keto diet. The keto approach severely restricts sugar and all carbohydrate sources in your diet, while increasing fat and protein consumption. 

Following this approach forces your body to burn fat for fuel, rather than glucose -- the body’s main energy sources, which is derived from carbs. When the body is in a fat-burning state like this, ketones are released into the bloodstream and the brain uses them for fuel, instead of glucose.

Most proponents of the keto diet suggest that a daily carbohydrate intake of fewer than 50 grams a day is key. In some cases, carbohydrate consumption can drop to as low as 20 grams per day. 

This is a huge difference from the Standard American Diet (SAD), which relies largely on refined carbohydrates. Most people are used to consuming hundreds of grams of carbohydrates per day and have been doing so for most of their lives. 

While most people these days are adopting a keto diet strictly for weight loss, there are actually many other potential benefits, including decreased inflammation, slower aging, and a lowered risk of developing Alzheimer’s disease. 

In fact, the keto diet was originally developed way back in the 1920s as a treatment for epilepsy and it’s still commonly prescribed to epileptic seizure patients to this day.  

What Is the Keto Flu?

The term keto flu is used to describe a series of flu-like symptoms, that occur in some people when first starting out on the keto diet. It’s also sometimes referred to as the “carb flu” since it takes place when carbohydrate consumption is suddenly (and drastically) reduced.

The symptoms are varied and may include nausea, headache, general fatigue, dizziness, dehydration, gastrointestinal distress, cramping, muscle soreness, poor concentration, trouble sleeping and reduced tolerance of exercise.  As you can see, it can feel a lot like the real flu, especially when multiple symptoms are present for a long period of time.

Generally, keto flu symptoms range in severity.  Some people may only have to deal with one or two symptoms, while others may suffer from many. Thankfully though, there are ways to lessen the symptoms. 

In general, someone who consumes large amounts of refined carbohydrates at every meal is much more likely to develop the keto flu. If you are already consuming moderate to low amounts of carbs, chances are your symptoms will be less severe.

What Are the Causes of the Keto Flu?

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Many changes can take place within the body as a person begins the keto diet, especially if they are transitioning from a high-carb approach. Several of these changes occurring at once is ultimately what leads to the dreaded flu-like symptoms. 

Micronutrient Deficiencies 

One of the most common causes of keto flu is believed to be micronutrient deficiencies. These may occur on a ketogenic diet because food like grains, legumes, and fruits are reduced or eliminated entirely. Common deficiencies include B vitamins and some minerals.

 Being deficient in micronutrients, even for a short period of time, can have several adverse effects on your health. It may be beneficial to take a multivitamin supplement when following a keto diet or to at least include foods with a healthy balance of micronutrients in your keto meal plan.


Dehydration, as well as electrolyte imbalances, can also contribute to the keto flu. Glycogen levels drop quickly when carbohydrate consumption is drastically reduced. This causes water stores to drop as well, since glycogen binds to water inside the body. 

As little as a 5% decrease in water inside your body can lead to dizziness and fatigue and symptoms get progressively worse as that percentage increases.  

The keto diet also impacts electrolyte balance in several ways. It restricts many foods that are naturally high in potassium. These include fruits such as bananas, starchier vegetables, and beans. At the same time, excess sodium is released as insulin levels go down, which happens quickly as carbohydrates are restricted.

Hormonal Changes

Several hormonal changes can also take place inside the body as a person adapts to the keto diet. Carbohydrate restriction can lead to a drop in the active thyroid hormone T3, especially when calories are restricted. (3)  

Drops in insulin-like growth factor (IGF-1) and leptin, typically take place as well. And if a person starting on the keto diet is not sleeping well, levels of the stress hormone cortisol will also naturally rise, causing mood changes and irritability. 

Abnormal cholesterol levels may be a factor as well, although a rise in cholesterol levels could simply be related to losing weight. Cholesterol levels often go back to normal, once weight loss stabilizes. There is also a subset of the population (estimated to be 5-25%) where LDL cholesterol levels can increase significantly on a low-carb approach. Either way, the fluctuation of cholesterol levels could potentially lead to keto flu symptoms.

How Long Does the Keto Flu Typically Last?

Thankfully, the keto flu usually only lasts about a week for most people, though some may experience symptoms for several weeks. If symptoms become persist or worsen, it’s important to seek medical help as they could be indicative of other health issues. 

As mentioned previously, the severity of the symptoms is almost always related to the number of carbohydrates the person was previously consuming. The higher the consumption was before starting the keto diet, the more severe the flu-like symptoms are likely to be.

Does the Keto Flu Effect Everyone?

The keto flu is common, but not everyone will experience it. A person who was already eating fewer carbohydrates is less likely to get the keto flu. And some people are just lucky and make a smooth transition to keto.

 You can also slowly ramp down your carb consumption if you want to avoid the keto flu. Spacing out your transition to the diet over the course of a couple of months from high-carb, to moderate-carb, to low-carb, can help to reduce your likelihood of experiencing unwanted side effects.

Photo by Christian Erfurt

Who Should Avoid the Keto Diet?

While the keto diet can be very effective for weight loss and inflammation, it is not suitable for everyone. It can put a strain on the kidneys since they have to work overtime to release the excess sodium that occurs when insulin levels decrease. Therefore, anyone with kidney disease or poor kidney function should not attempt the keto diet. 

People who have a history with eating disorders also should not attempt the keto diet. The somewhat restrictive nature of the diet can potentially have a negative impact on your eating habits. 

through reducing your carbohydrate intake, the keto diet can be helpful in managing type 2 diabetes; however, type 1 diabetics are not advised to follow the diet unless there is direct medical supervision. 

Pregnant women should not follow the keto diet or any other type of restrictive diet for that matter -- you should stick to the dietary guidelines given to you by your physician throughout your pregnancy.

How to Recover from The Keto Flu

Now that you understand what the keto flu is and what causes it, you're probably wondering how to recover from it. The good news is, there are many ways to hasten recovery, and in some cases prevent the symptoms from occurring in the first place. 

Drink Plenty of Water

Dehydration can easily occur in the beginning stages of the keto diet as the body adapts to the changes in insulin levels. This dehydration, in turn, may lead to fatigue, nausea, and even muscle cramping.

It appears quite obvious in hindsight, but the simple solution here is to drink more water. Keep a glass or bottle of water next to your bed, in case you wake up thirsty. Drink water as soon as you get up, as we lose water while we sleep. Also, make sure it’s always available to sip on throughout the day. 

Other fluids are useful too, such as broths and teas, as long as they don’t contain sugar. And try to avoid too many caffeinated beverages, as they can interfere with sleep.

Consume Electrolytes

Consuming electrolytes can be helpful with keto flu symptoms as well. It’s important to consume sodium, potassium, and magnesium in the proper ratios to stay hydrated and feeling well. 

Adding some additional salt to your meals and choosing keto-friendly foods high in potassium and magnesium, can also be helpful.  There are also sugar-free electrolyte products that contain a proper balance of minerals specifically designed for keto dieters. Products like this can make the transition to keto much easier.

Take In Plenty of Micronutrients

Deficiencies in micronutrients can also contribute to the flu-like symptoms. Eating nutrient-rich foods such as dark leafy greens and grass-fed beef will be helpful. In addition, this may also be the ideal time to start taking a good multivitamin supplement to fill in the gaps and replace the micronutrients that your diet is not providing.

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Eat Plenty of Healthy Fats

Another way to make the transition easier and reduce the severity of your symptoms is to make sure you are consuming enough healthy fats. This means fats like coconut oil, avocados, nuts and eggs. This helps you feel satiated and reduces the carbohydrate cravings that typically occur at the start of the keto diet.

Get Enough Sleep

Common complaints of people beginning the keto diet include fatigue and irritability, indicating a need for more sleep. Avoid using caffeine to power through the day. Instead, limit your use of caffeine (a noon cut-off time is usually wise) so it is easier to fall asleep at night. 

Work on developing a relaxing bedtime routine. A warm bath, lavender oil in a diffuser, or reading a book before bed (rather than surfing the internet), can all contribute to better sleep. Waking up at the same time every day can also lead to more regular sleep and a reduction in keto flu symptoms.

Cut Back on Strenuous Exercise in the Begining 

If you are already feeling fatigued and having some muscle cramps, the last thing you need is strenuous exercise. When transitioning to a keto diet, try moving your body in less strenuous ways. This is the perfect time for activities like yoga, gentle stretching, long walks, and leisurely bike rides. Save the higher intensity activities for when you are more adapted to the keto approach.

Wrap Up

The term keto flu refers to a series of symptoms that may occur in the first few weeks of starting a keto diet. While the keto flu is not the same as the real flu, it can feel every bit as miserable. Thankfully, there are several things you can do to reduce the severity of your symptoms (or even eliminate them altogether).  

Consuming an adequate supply of water and electrolytes, as well as taking in plenty of micronutrients are all effective ways to reduce your chances of experiencing debilitating side effects when starting the keto diet.  

While the keto flu is common, not everyone will be affected.  Particularly those who come into the diet with a lower carbohydrate consumption will typically be less likely to experience negative symptoms during the transition process. 

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