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What’s the Keto Flu & How to Cure it

Last updated: Oct 24, 2020 at 9:20AM | - Published on: Oct 22, 2018

Written by Sarah Neidler, PhD

Scientifically Reviewed by Raphael Sirtoli, MSc

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The keto flu or low-carb flu is the most common reason why most people don’t stay on a keto or low-carb diet. They start restricting carbs, feel terrible and decide that it’s not for them. What they don’t know is that it would have taken only a few more days for the flu to be over and to feel great.

What is a keto flu?

A keto flu is not dangerous, and it’s not actually a flu since it’s not caused by a virus. What it is, is symptoms of carb withdrawal – specifically junk carbs with sugar and flour.

But most people indeed experience flu-like symptoms. They have low energy and feel weak, are not able to concentrate and would like to stay in bed all day. Nausea, headaches, irritability and trouble sleeping are also common. Some people even have severe symptoms such as diarrhea and low blood pressure.

The severity and duration of the symptoms varies a lot between individuals. Some people hardly notice anything, others feel terrible for a day and others for a couple of weeks. It also depends on your health status, lifestyle and nutrition before starting keto

When you’ve been eating lots of sweets, refined carbohydrates (flour) and low-fat foods, the keto flu might be a bit more severe than for people who’ve managed to avoid these more so. Make no mistake, what you’re experiencing are symptoms of carb withdrawal.

Causes of the keto flu

Once you understand what causes the keto flu, it will be easier to get over it. There are two main causes of the keto flu, carbohydrate withdrawal as we said and the ensuing lack of electrolytes, which is when the keto flu starts [1].

Carbohydrate withdrawal

The keto flu adaption phase happen when you lower your carbohydrates intake to 5% of your daily macros. When you swap carbs for protein your body will start to be in ketosis

Carbohydrates are used as energy after first being broken down to simple sugars. For most of us, they’ve probably been a primary source of energy for most of our life. Your body is simply used to that. In ketosis, our body burns much more fat for energy, so much so that it also produces ketones from all that fat.

By eating so many carbs that excessively raised your insulin, you limited your body’s access to fat stores and thus fat burning. You probably eat three times a day, each meal containing a whack of carbs.

Even after dinner, you eat a high-carb snack like chips or a fruit juice that’s chock full of sugar. First thing in the morning: toast for breakfast and sugar in your coffee.

And who needs that much sleep (7 – 8 hrs) anyways? This means that your overnight fast is even shorter and you were busy burning off that late-night carby snack. You missed the chance to access your own fat stores that provide you with stable energy required for regenerative sleep.

Did you know?

Fasting is the fastest and simplest way to get into ketosis because it drops insulin like a rock, allowing your body to access more complety access its stored fat [2]. Once you are in ketosis, the keto flu will soon be over, anywhere from a couple of days most commonly to a couple of weeks more rarely.

Most people enter ketosis after 24 – 48 hours of fasting (only drinking water). After this, the only challenge is to stay in ketosis.

Many initially achieve this by restricting carbohydrates to 20g per day. After a while, you may well tolerate a bit more carbs and you can gradually increase your daily carb intake.

At first, it’s worth measuring your ketones to make sure you’re not kidding yourself. Same goes for blood glucose. Intermittent fasting, on the other hand, makes it easier to stay keto. This is where you eat within an 8-hour window and fast for the remaining 16.

Regular carb-heavy meals tend to keep your insulin levels higher than healthy, preventing fat burning [3]. We’re talking about worst carb sources, like pizza, pasta and cake, and less so the better ones, like carrots, turnips and berries.

That means that your body is ‘out of practice’ when it comes to efficient fat burning, not to mention ketone production (ketogenesis). To start doing so again there’s all the machinery we need deep in our cells, but we need to give them the proper signals to reactivate.

Glucose metabolism (carb burning) requires a different set of molecules and enzymes than ketone production. Before your body can produce ketones and use them as a source of energy, it first has to make more of some enzymes and less of others over a couple of days.

In the meantime, your body lacks energy which is why you feel tired and lethargic. Moreover, junk-carbs like pasta and sweets can be very addictive. In this instance, if you suddenly take them away, the symptoms of carb withdrawal aren’t all that different from taking cocaine away from an addict. In both cases, the withdrawal is unpleasant but not dangerous and people can get over the symptoms quickly.

Lack of electrolytes

During the keto flu adaption when your body lose water you lose electrolyte. There are 3 main electrolytes you need to carefully watch during the keto flu, magnesium, potassium and sodium.

When you switch from a high-carb to a ketogenic diet, you will notice that you lose a lot of water. As a side effect, you go pee more frequently. The reason why you initially lose so much water is because when you store a gram of carbs as glycogen in your muscles and liver, you also store ~ 3 – 4 g of water with it. Glycogen binds water together with electrolytes.

As you deprive your body of carbs, you will first use up your glycogen stores. For this reason, it is essential to replenish the minerals and electrolytes lost with that water when adapting to a keto diet.

Here is the list of the main electrolytes (or minerals) you need to keep an eye on, especially during the keto-adaptation phase:

  • Sodium: To make up for the lost minerals and electrolytes, the first and easiest thing to do is to salt your dishes liberally. This means anywhere from 4 to 7 g a day. Just as we recommend ‘drink to thirst’ we recommending ‘salt to taste’. Because you stopped eating fast food and ready meals, your salt intake will already have dropped. Table salt consists of sodium and chloride which are both essential electrolytes, meaning you can’t survive without them. Don’t fear salt!


  • Potassium: When supplementing initially try to stay on the high end of 2 to 5 g of potassium a day, on top of what’s in your food. Most vegetables and mushrooms are excellent potassium sources but when you boil the them a lot of potassium is lost in the water. Make sure to either reuse the water or cook them without boiling them e.g., by frying them in a pan with butter. The fish halibut is a good source, providing 600 mg in a 113 g serving.


  • Magnesium: Most people don’t get enough magnesium. In this adaptation phase, try to get around 400 to 600 mg a day on top of whatever your food contains. Nuts and seeds contain high amounts of it, as does as cocoa, but you’ll only absorb a minority of it because the seed tries to keep it for itself. If you eat these kinds of foods regularly, you might not have to supplement long-term. But in the transition phase, it certainly makes sense. We recommend Magnesium citrate or Magnesium chloride for example because they are easily absorbed.


  • Calcium: When you eat milk products or other animal foods like sardines and small fish you get more than enough calcium. In case you don’t eat dairy avoid supplementing it and get it from small fish instead. Calcium supplementation is not risk-free and doesn’t really work. But if you do supplement with it, consult a nutritionist or doctor. Also, realize that depending on where you live your water may already contains more calcium than is optimal.

Another way to get plenty of minerals is to drink bone broth. Bone marrow is replete with nutrients and minerals. The best way to access all these goodies is to simmer bone marrow in a pot for several hours. The result is a delicious and healthy bone broth. You can use the broth for soups and stews or just add some salt and pepper and drink it. It provides all the minerals you need to recover from the keto flu. Try to get used to it, bone broth is an excellent addition to any diet, not only to keto.

And if you don’t do bone broth, just simmer seasoned meat-on-the-bone for 1 to 2 hours in a bit of water and tasty fat.

Tips to start the keto diet and how to avoid the keto flu

There are basically two ways to start a ketogenic diet. The first option is to eliminate all high-carb foods from your diet from day one while restricting your carb intake to 20 g per day.

The second option is to lower your carb intake gradually. That means that you’d first eliminate sodas, then sweets and desserts. Next to go would be starchy foods like pasta, bread and potatoes. The last step would be to only eat things like fish, meat, eggs, nuts and seeds, low-carb vegetables and fermented full-fat milk products.

Which way is best for you? Depends on what type of person you are. For some people, it works better to change everything at once, radically. The more strictly you follow the ketogenic diet, the faster you’ll be in ketosis. If you’re OK gradually replacing carbs with fat, the keto flu symptoms might be milder, but it will probably take longer for you to be in ketosis and fully keto-adapted.

Whichever option you choose, here are some ‘keto flu remedies’ that will help you hit the ground running:

1)   Choose your moment wisely: Don’t pick a work week full of important meetings demanding your full attention. Holidays could work if you’re looking forward to the switch rather than dreading it. Although being away from home can make it difficult to control what you get to eat. You probably eat a lot at restaurants where you don’t know what ingredients were used exactly. Hidden carbs (and seed oils) are the rule rather than the exception, unfortunately.

2)   Don’t change too many things at once: Many people are over-enthusiastic and want to change everything at the same time. Change their diet, exercise more, be more productive at work. This is understandable, and I don’t want to take away the enthusiasm that gives you the much-needed momentum to make big changes. Joining a gym the same week you’re keto-adapting is unnecessary for most people. Your body has to get used to its new source of energy and demanding more from your body than usual, if you’re not used to working out, will be hard. So be patient. Once the keto flu is over, you will feel more energetic than ever before, and nobody will be able to stop you from going to the gym!

3)   Get enough sleep: You should also make sure to get enough sleep during the transition time. Go to bed on time and try to get your 7 to 9 hours of sleep [4]. Interestingly some people report feeling more rested from the same amount of sleep once keto-adapted.

4)   Don’t restrict calories: Even if your goal is to lose a lot of weight, when starting out don’t intentionally restrict calories. Make sure you eat plenty of nutrient-dense fatty animal foods so that your body learns to rely on these good sources of energy. After all, you’ve just restricted your body’s most used energy source so introducing a good substitute is crucial. So make sure that you get at least enough of the new one, even if you’re still struggling to use it optimally.

5)   Drink to thirst: You’ll lose quite a bit of weight during the first few days. How much depends mostly on your initial weight, percentage body fat and how much water you retain. As is typical, you may also be eating more protein in a single sitting on this diet which can increase your thirst as well. Some people end up drinking 3 liters or more and you thus go to the bathroom more often. But some people do the mistake of forcing themselves to drink a lot throughout the day when there’s no need for that.

You will learn in a simple visual infographic, what's the keto flu and what to do about it.

How Nutrita helps you to get over the keto flu

Nutrita provides you with insulin index and more importantly here, a Keto Score, helping you to get into ketosis with nutritious foods and stay there.

Since your body will be working double-time to adapt to burning lots of fat it only makes sense to support it with a nutrient dense diet. Getting your body all the essential nutrients it needs, including electrolytes, will make keto-adaptation shorter and less burdensome.

You will be able to track how much salt, potassium and magnesium your taking in and if you don’t know how to balance them Nutrita will show you how.

What happens once the keto flu is over?

The ketogenic diet, if practiced correctly, is incredibly nutrient dense. It contains plenty of vegetables, nuts, seeds, eggs and healthy fats. Meat is also an essential part of the keto diet unless you decide to go for a keto vegetarian or keto vegan diet.

It is also common to eat offal, stuff like liver, brain, kidneys, tripe etc.. which are by far the most nutrient dense foods – full stop! Yes, few people like them. The have a distinct, strong, gamey taste. Give it a try, it’s worth it.

Offal doesn’t only increase your selection of animal foods, they’re also bursting with essential micronutrients. 100 g of beef liver, for instance, will give you tons of the active form of vitamin A called retinol, enough to last you a few weeks. So it’s not like you have to eat it daily…


The keto flu is a hurdle, but don’t let it stop you from starting a ketogenic diet. People have different experiences keto adapting and it is not uncommon to hardly notice the shift.

The keto flu is caused by carb withdrawal and a lack of electrolytes. Make sure you make things easier for yourself during that adaptation phase: choose a good, lower stress moment to give it a try, and buy the mineral supplements and appropriate foods in advance.

If you’re experiencing the flu don’t worry it’ll go away fast, you’ll feel better than ever shortly thereafter. In the meantime, Nutrita will support you, so know we got you covered!

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Written by Sarah Neidler, PhD

Sarah Neidler did her PhD in cancer research at the Beatson Institute for Cancer Research in Glasgow. She has a strong interest in nutrition and the ketogenic diet and believes that they are beneficial for the treatment and prevention of chronic conditions, such as heart disease and diabetes. She loves cooking, reading, sewing, Yoga, and CrossFit.