Keto Flu: What You Should Know Before Doing the Keto Diet

Have you ever heard of the keto flu? It’s a term associated with the ketogenic diet and something many people experience first before knowing about. Here, you’ll learn what the keto flu is all about — the cause, duration, and symptoms, among others. Check out our comprehensive guide below.

What is the Keto Flu?

The keto flu refers to several symptoms a person may experience once they start the keto diet. These are collectively referred to as the keto flu because of how similar they are to symptoms of having influenza or the flu. But instead of viruses, what causes the keto flu is your shift to the low-carb ketogenic diet.

As you may have already known, the keto diet relies on your body adapting to the state of ketosis. This is when your body starts to lose carbohydrates and glucose for energy. Once this happens, your body turns to fatty acids. The stored fat is used and you get ketones, which your body can use for energy.

But while it’s generally safe to reduce your daily carb intake to below 50 grams and go into a state of ketosis, the symptoms aren’t all exactly desirable — there are good and bad ones. The unappealing symptoms form the keto flu. It’s your body telling you that it’s suffering from carbohydrate withdrawal.

Still, the severity and duration of each symptom vary from one individual to another. It’s not contagious like the flu, but you wouldn’t want to experience if either way. The good news is that the keto flu is temporary — the symptoms will fade away as your body gets used to a low-carb diet.

What are Symptoms of Ketosis Flu?

You don’t have to experience every single symptom to say that you have the keto flu. Having even just a few of these for several days is indicative that you do have it. But in order to identify whether you do have it or not, it’s important to know all the possible symptoms associated with starting the keto diet.

1) Diarrhea and Constipation

Issues related to your gastrointestinal tract aren’t so uncommon when starting the keto diet. What could be going on is that the enzymes in the small intestine cannot cope with all the fat you’re suddenly consuming. Then, the fat is taken to the colon and leads to bacteria that contribute to gas problems.

Moreover, it’s worth noting that fats stay longer in your stomach than other nutrients. This is good in a way: You feel fuller more often. But the same fats can also lead to abdominal pains and vomiting. Even on a keto diet, you shouldn’t forget to have dietary fiber — the beneficial type of carbs.

Not consuming enough fiber will affect your digestion. It is essential in keeping the gut bacteria well-fed and to keep the cells in your colon healthy. Symptoms like diarrhea and constipation shouldn’t last for a month. Blood in the stool is also a problem. If these happen, you need to consult your doctor.

2) Sugar Cravings

Sugar is not just found in chocolates and sweets. Many foods such as cereal, soft drinks, canned soup, and even ketchup have refined sugar. As you switch to a low-carb diet, you could easily find yourself craving for any of these foods — even if you don’t have a sweet tooth, to begin with.

3) Fatigue and Muscle Problems

The headache you feel upon starting the keto diet is due to all the water and electrolytes you are losing. Electrolytes such as sodium, potassium, and magnesium are important in hydration and the regulation of your nervous and muscular systems. Without them, you’re bound to develop fatigue.

While it’s common for people to drink lots of water after a workout, not everyone is aware of why it’s important. Not having enough hydration could cause cramps and aching muscles. In particular, cramps are due to a low amount of potassium in your body — these electrolytes help your muscles contract.

Furthermore, you might experience muscle pains because of your low-carb intake. If you’re regularly doing physically intensive activities, your body relies on carbs for energy. These are stored as glycogen and are burned to fuel your body. And when these run out, your body switches to your stored fat.

While ketones can also keep you going while at the gym, it’s important to know that high-intensity workouts are better done with more stored carbs than stored fat. So if you’re starting a keto diet and you still want to do interval training, you could feel sore for several days after.

4) Insomnia

One reason you may have trouble sleeping during your keto diet is that you lack dietary fiber. You should still consume them since they are good for your body. For example, tart cherries have fiber and melatonin — the hormone responsible for regulating your sleep schedule.

Likewise, foods such as whole grains contain magnesium. This electrolyte helps you sleep better through the maintenance of the gamma-aminobutyric acid (GABA) neurotransmitter. Starting the keto diet without it will affect your sleep. Plus, your body needs to adjust to the new diet.

Even the healthy fats you consume can contribute to your temporary bouts of insomnia. While butter and coconut oil have medium-chain triglycerides (MCT) to help burn the fatty acids, you may get too much energy. This then causes you to stay awake all night and wake up earlier than expected.

5) Nausea

Another symptom of the keto flu is nausea, which includes a variety of physical conditions. Aside from getting headaches, you may get dizzy and even feel like vomiting. One possible reason is that going on a low-carb diet temporarily lowers the level of blood sugar in your body — resulting in hypoglycemia.

6) Lack of Focus

This is an interesting symptom because the direct opposite happens in the long run. While you may have problems concentrating at work or school, you could feel more productive once you’re several weeks into your keto diet. The so-called brain fog becomes replaced with better mental clarity.

When Does Keto Flu Hit?

The keto flu starts during your first week of switching to the keto diet. The first day may seem like nothing’s changed, but you will start to feel a symptom or two after three or five days. The time depends on how you approach the keto diet — whether your carb restriction is severe and quick or not.

How Long Does Keto Flu Last?

Usually, the keto flu lasts only between a couple of days and about three weeks. You may even have the symptoms for a whole month. But if any of the symptoms continue well beyond four weeks and they are getting more severe by the day, you need to consult your doctor immediately.

Why Do People Get the Keto Flu?

Not everyone who starts the keto diet suffers from the symptoms under the keto flu. Some only have it for a couple of days while others could have it far longer. So why do some people get it? It’s because each human body reacts differently to a low-carb and high-fat diet.

For example, imagine a person eating a lot of white rice, pasta, and bread on a regular basis. They’re used to gaining carbs every single day. If they decide to start the keto diet, they would have to moderate their favorite foods. Thus, their bodies will experience a more drastic shift in terms of nutrition and diet.

But if you were already eating a moderate amount of fat and protein along with the usual carbs, you may have a better transitional period than others. Your body isn’t necessarily new to using stored fat when you run out of glycogens Consequently, factors such as genetics and dehydration should be considered.

How to Avoid It

If you don’t want to experience the keto flu, you have to be careful with your keto diet. Don’t rush into this process — reduce your daily carb intake day by day instead of having one big drop. You must also drink lots of water and have enough electrolytes to prevent many of the aforementioned symptoms.

In addition, do not severely reduce your daily calorie intake. A diet that’s low in both carbs and fat is going to cause a variety of undesirable symptoms. Don’t forget that the keto diet is about replacing foods high in carbs with those that are high in fat. It’s not about making yourself hungry all the time.

How to Get Rid of the Keto Flu

While the keto flu is a temporary health condition, there are several ways to immediately get rid of them — or at least lessen their impact on your body.

1) Consume Enough Fat and Carbs

Craving for sugary and carb-filled foods is normal when you’re just starting the keto diet. Luckily for you, these cravings will eventually fade, especially if you eat more fatty foods. Along with protein and dietary fiber, the increased fat in your body will make you feel full longer and have fewer cravings.

Reduce the number of carbs in your daily meals in a gradual manner. Don’t do it all at once because you’re going to put yourself more at risk of the keto flu. With each reduction in carbs, add in a bit more fats and protein. This way, your body’s metabolic functions won’t face drastic and sudden changes.

2) Drink More Water and Get More Electrolytes

Staying hydrated is important no matter your diet. But when you’re on the keto diet, drinking more water than the usual eight glasses is important. You’re going to lose electrolytes and water quicker. Why? Having fewer dietary carbs means fewer glycogens, which leads to increased water loss in the body.

Drink around 2.5 liters of water. You can also check your current weight and divide that in half. The resulting quotient is the total amount of water in ounces that you need to drink each day. If you keep this up, your muscle and stomach pains will go away quickly.

Furthermore, look for food to replenish your electrolytes. Dairy, bananas, and avocados are all keto-friendly options that will boost your electrolyte count as well. You can even take supplements containing potassium and magnesium, among others, to alleviate muscle pains and headaches.

3) Stick to Light Physical Activities

Having an active lifestyle is essential in losing weight and staying healthy in the long run. However, you should stick to lighter activities such as walking and yoga during the first month or so of your keto diet. Avoid doing any high-intensity workouts while your body is still adapting to its new source of energy.

4) Get More Sleep

Having troubles with sleeping is not only bad for work but also for your health in general. You need sleep to rest your brain and manage your cognitive functions. Staying all night could make you irritable and groggy all day as your body develops more of the stress hormone known as cortisol.

One way to combat insomnia is by taking a bath before going to bed. This will relax your body and prepare it for a good night’s sleep. Turn off the lights and stop yourself from checking your phone or computer. And lastly, avoid taking any stimulants such as coffee or energy drinks at night.


The keto flu isn’t a requirement for you to achieve a state of ketosis. While the symptoms under it are indicative that your body is adapting to a low-carb and high-fat diet, they do not have to happen all at once. Likewise, their duration and intensity differ from person to person.

There are ways to avoid the keto flu — and the same holds true for getting rid of the symptoms. Just remember that it’s a temporary condition. If you still have it after a month and you’re very unwell, go to your doctor as soon as possible.

We hope our guide helped you understand what the keto flu is all about. Feel free to send us a comment for any questions.