Keto Flu: What It Is, Symptoms and How to Get Rid of It - Perfect Keto

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Keto Flu: What It Is, Symptoms and How to Get Rid of It


The ketogenic diet is a low-carb diet with moderate protein and high fat that can help you lose weight and maintain your health. 


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Normally, your body burns carbs for fuel. On keto, you cut carbs out of your diet, training your body to burn fat instead. 

Staying in a fat-burning state comes with a lot of health benefits, and it’s great for long-term, sustainable weight loss. 

However, your body can take a week or so to get used to such a big metabolic change. When you’re first starting out on keto, you may experience “keto flu” — a few days of flu-like symptoms as your body learns to switch over from burning sugar to burning fat. 

The good news is that there are a few simple tips and tricks to relieve — and even prevent — keto flu. 

This article will cover why keto flu happens, keto flu symptoms, and how you can get rid of keto flu. 

What Is the Keto Flu?

The keto flu is a temporary collection of flu-like symptoms you might experience in the first week or two of starting a keto diet. 

Keto flu happens because your metabolism needs time to adjust to running on fat instead of carbs.

When you eat carbs, your body burns them as its main source of energy. But if you drastically reduce your carb intake — like on a low-carb ketogenic diet — your body depletes your glucose stores and starts burning fatty acids for energy instead. 

This metabolic switch is what causes keto flu — your body is still looking for carbs because it hasn’t yet figured out how to burn fat for fuel efficiently. Keto flu passes once your body gets out of carbohydrate withdrawal and adapts to burning fat for fuel.

Symptoms of Keto Flu

When you’re new to keto and first reduce your carb intake, you may run into the following common symptoms:

  • Fatigue
  • Brain fog
  • Nausea
  • Irritability
  • Diarrhea or constipation
  • Muscle cramps
  • Trouble falling or staying asleep
  • Sugar cravings
  • Low energy levels

How Long Does Keto Flu Last?

Symptoms usually occur within the first day or two of starting your new diet. How long the keto flu lasts varies from person to person. Some people don’t get the keto flu at all, while others could experience it for close to a week. 

Either way, the symptoms shouldn’t last more than a few days and should go away once your body is adapted to burning fat for fuel.

One thing to remember: keto flu isn’t dangerous and it only lasts during your transition into ketosis before disappearing for good. During that time, however, you may experience side effects like fatigue, trouble focusing, sugar cravings, and headaches. 

If keto flu presents over and over again, you might be going in and out of ketosis. Check your diet for hidden carbs and make sure to track your macros — especially during the first month or so.

Causes of Keto Flu

Some people have more metabolic flexibility than others — they can switch between burning glucose and burning fat with ease[*]. 

But if your body isn’t quite as metabolically flexible, you may end up with keto flu. Many people do — the main cause of keto flu is adapting to ketosis

However, there are a couple of other reasons that people get keto flu or reasons that keto flu symptoms are more severe. 

Dehydration/Electrolyte Imbalance

When you eat carbs, your body stores some of them as reserve energy. These stores are like an emergency energy fund in case you run out food.

During the first few days of keto, your body burns through all your carb stores (glucose stores). It’s only after your carb stores are gone that your body gets into ketosis and begins burning fat.  

Carbs require a lot of water for storage, so as you work through your carb stores, you lose a lot of water weight. Most people drop between 3-8 pounds of water weight in their first couple weeks of keto. 

When you lose all that water, it’s easy to end up dehydrated. You also lose electrolytes with that water, which can cause electrolyte imbalances. 

Dehydration and electrolyte imbalances often account for the fatigue, headaches, and muscle cramps that happen during keto flu. 

Not Eating Enough

You may not be used to eating a low-carb, high-fat diet at first. It’s easy to under-eat during the first couple weeks of keto, which can cause low energy and trouble concentrating. 

When you’re transitioning into keto, it’s not the time to cut calories. Make sure you’re getting plenty of high-fat food. 

Eat lots of fatty meat, salmon, butter, olive oil, coconut oil, avocados, fresh greens, etc. You want to nourish your body with plentiful fat and protein, especially for the first couple weeks of keto. 

Once you’ve transitioned into ketosis, if your goal is weight loss, you can cut back on calories. But for the transition, you want to eat a lot. It’ll make keto flu much easier. 

Remedies and Prevention for Keto Flu

If you’re experiencing the keto flu, these steps will help you get rid of it faster, or at least lessen the symptoms.

Stay Hydrated

Drink lots of water during your keto transition. You’re losing multiple pounds of water weight as you burn through your carb stores, and you want to replenish that water to avoid dehydration. 

Drink plenty of water throughout the day to help reduce symptoms like headaches, fatigue, and nausea. 

  • Keep a reusable water bottle near you, filled at all times so you can drink it wherever you are.
  • Always drink when you feel thirsty, but try to catch it before thirst strikes.
  • Drink most of your water during the day so you’re not waking up in the middle of the night for a trip to the bathroom.

Replenish Electrolytes

Your body doesn’t contain pure water. Your cells are bathed in saltwater that contains electrolytes like calcium, sodium, potassium, and magnesium. 

When you lose all that water weight, your kidneys begin excreting electrolytes to go with it[*]. As a result, you can end up low on electrolytes. Make sure you replenish them by:


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  • Increasing your sodium intake. This will help counteract the water loss that happens when starting a keto diet and replenish sodium. Salt your food heavily; you don’t have to worry about it increasing your blood pressure, because when you’re on a low-carb diet, your insulin stays stable and low, which sends a signal for your kidneys to continuously excrete sodium[*]. 
  • Supplement with magnesium. Some rich food sources of magnesium include avocados, pumpkin seeds, cooked spinach, halibut, cashews, salmon, macadamia nuts, and dark chocolate[*][*][*].
  • Eat potassium-rich keto foods. Potassium is another key mineral that should be on your radar but probably isn’t. This electrolyte is involved in heartbeat regulation, muscle cramping, energy production, bladder control, and body temperature[*]. If you’re feeling any issues connected to these areas, consider adding more potassium-rich foods like avocado, Brussels sprouts, mushrooms, zucchini, and pumpkin seeds to your keto meal plan.
  • Eat calcium-rich keto foods. Broccoli, leafy greens, chia seeds, sardines, and salmon are all packed with calcium. And bone health isn’t calcium’s only job. It’s also vital for blood clotting, muscle contractions, and good cardiovascular health[*].
  • Take an electrolyte supplement. If you need instant relief, taking an electrolyte supplement will help replenish your levels faster than foods can. Check out the vitamin and mineral supplement guide for more information.


Your exercise performance may temporarily suffer while your body is adapting to higher fat and lower carb intake. So while you probably won’t hit a personal record during this time, that doesn’t mean you should stay in bed.

Getting light exercise 2-3 times per week can burn through your carb stores faster and increase your metabolic flexibility, which helps relieve keto flu symptoms more quickly[*]. 

Low-intensity aerobic exercises — such as walking, swimming, or practicing yoga — are good choices during a keto transition. Heavy lifting, CrossFit, and other intense exercises may be difficult until you’re in ketosis. You can certainly still do them, but you may struggle a little more than usual. 

Once your body gets through the keto transition, you should be able to resume your normal exercise routine.

Increase Fats 

Since your body is no longer getting its energy from carbohydrates and sugars, it needs plenty of fat and protein for fuel.

This means you’ll need to make sure the calories you used to get from carbs are partially replaced by eating plenty of keto-friendly fats.

Some good keto fat sources include:

Increasing your fat consumption while reducing your carbohydrate intake will help ease your transition. You’re encouraging your body to use fat for energy, and giving it plenty of resources to do so.

Supplementing with MCT oil can also help you beat the keto flu by increasing your ketone levels, which can make the switch from carbs to fat less uncomfortable. 

If you find the keto flu lasts longer than a week, re-evaluate your macros. You might still be eating too many carbs and not enough healthy fats.

Sometimes people think they’re transitioning into ketosis when in reality hidden carbs might be holding them back.

Take Exogenous Ketones

Remember, one of the reasons you may have the keto flu is because your body is trying to create and use ketones (made from fat) for energy, but it isn’t quite good at it yet. 

One way to help mitigate keto symptoms is to add exogenous ketones to your morning routine.

These energy molecules are the same ketone bodies your body naturally produces, in supplement form.

Unflavored Keto BHB Capsules will flood your system with ketones so you get some of the benefits of being in ketosis before you’ve even burned through your glycogen stores.

You can use exogenous ketones during your initial transition or anytime you want a quick boost of energy and mental clarity.

How to Avoid the Keto Flu Entirely

If you’re just starting the keto diet and want to avoid keto flu entirely, follow the steps below.

Follow a Nutritious Ketogenic Diet

One of the main reasons beginner keto dieters start to feel unwell on keto is the lack of proper micronutrients.

The ketogenic diet is not just about macronutrients. You could technically hit your macros by eating nothing but cottage cheese, but you’d end up with electrolyte and other nutrient imbalances, which would contribute to keto flu. 

The key to transitioning to keto with few to no side effects is starting with a nutrient-dense ketogenic diet that covers all your vitamin and mineral needs. 

Here’s a list of all the healthy foods you can eat on a ketogenic diet. Bone broth is especially popular with people transitioning into keto. 

To make your life easier, follow this 7-day meal plan to get used to eating keto.

t’s also important you avoid unhealthy foods that raise your blood sugar, insulin levels, and kick you out of ketosis.

Get Plenty of Sleep

Getting at least seven hours of sleep a night is important for anyone, and even more so for keto dieters. Your metabolism is getting used to switching fuel sources, so getting plenty of sleep can help reduce stress and fatigue.

Your body may need more sleep during your keto transition. Give it that luxury; you’ll feel a lot better for it. 

If you struggle to get enough sleep at night, try taking a power nap or two during the day. You can go back to your normal sleep schedule once you’re in ketosis. 

Take Supportive Supplements

The easiest way to avoid side effects when you first start keto is to take the right supplements from the start.

Your keto diet should be based on healthy whole foods, but supplements can help fill in any nutritional gaps and make your life easier.

Here are four supplements you can take to ease your keto transition:

The Takeaway

Keep in mind that if you experience any flu-like symptoms, they will subside. Just give it time.


Join 90k+ people who are losing weight with Keto Kickstart, our doctor-developed program designed to give you real weight loss results.

Once the hard part is over, you can enjoy increased energy, weight loss, mental clarity, and all the other benefits of ketosis


16 thoughts on “Keto Flu: What It Is, Symptoms and How to Get Rid of It

  1. This was very helpful. I’m experiencing at least half of these symptoms and am really struggling so will incorporate some of your suggested helps.

  2. I’ve been on the keto diet for about 45 days, ad no issues at first but now I am experiencing many of these symptoms. Any ideas on why this is happening?

  3. Been on it for almost a month. I have sour stomach, weakness, sleeping is off, dizziness, light headedness and just feel like crap. Need to exercise but don’t have energy.

  4. I’m only two weeks into it I get to sleep just fine it’s staying asleep what’s hard. I woke up today with no energy and feeling like I had to vomit. I went back to sleep till 3 pm. I hope this goes away fast cause I have work and a family to take care of. I don’t want to cut my self short and cut my self off this diet cause it is working.

  5. Two weeks in and yesterday felt hot and sweaty with tummy pains… diarrhea. Urine test strip was dark purple so lots of ketones in my wee. Feeling hot and sweaty.
    Strangely though feel like my fibromyalgia brain fog has completly lifted and have more energy. Doing intermittent fasting and having two meals in an eight hour window.
    Going to soldier on but cant be too far from the toilet today lol.
    PS….not hungry

  6. The trick to this is not to cut carbs out drastically. Many people go crazy limiting themselves to 20g of carbs when your body is used to hundreds. The key to success is to slowly cut back on carbs until your body reaches 20-25g tolerance.

  7. I have learnt a lot from this explanation. I am feeling some of the symptoms. I have a terrible headache for which I take Tylanol. I hope to get out of this state quickly. Iam seeing results from the low carb diet.

  8. How do I know if I have keto flu or real flu or allergies? The keto test strips say I only have a small number of ketones. So, does that mean I can’t have keto flu? One weird symptom I rarely get with flu or allergies is I am very light-headed when I stand up.

    1. Hi Dawn, common symptoms of keto flu are headaches, tiredness or lack of motivation, lethargy, brain fog or confusion and irritability. If you experience this, we recommend to stay very hydrated and increase your salt intake. Also, be sure you’re eating enough.

  9. For me it is a little different, I stopped eating Bread, rice last year and ofcourse sugar. Then I stopped most of the potatos and pasta. Maybe on of the once a week. Everything fine! Then last month a tried the 5 day water fast, used some salt every day, Keltic salt. The last day at the end I started to feel like having a flu. Before I started the fast, I have to mention, I was in full Keto. So 2 hours before the 5 days ended, I stoped. It took 16 hours to feel better.
    Last week I have tried again. Now the 3th day I became sick, no power, realy bad. I continu 24- hours, but the I stopt. After now 2 days, slowly I star to feel better. What is the reason for this?? I am still in Ketosis

    1. Hi Jel, within the first 2-4 days of beginning a keto diet, a common side effect is known as the “ketosis flu” or “induction flu” because it mimics the symptoms of actual flu. We recommend to stay very hydrated and increase your salt intake. Also be sure you’re eating enough.

  10. I’ve only bee doing the Sroldiet for six days. I have lost seven pounds and felt fine until tonight. I woke up aching all over my body feeling cold. I mean really aching! I’ve never had the flu but I imagine it’s like this. I literally lived on sweets and carbs. So I’m sure that’s it. I craved water when I woke up like this and I understand that’s normal. I’m not giving up!

  11. Thank you for this vast amount of specialised information. I am delighted (with a natural degree of excitement) to have found your Perfect Keto site.
    A few years ago I sampled the benefits of intermittent fasting but I failed to read any connection with the Ketogenic lifestyle, so I continued ignorant of such.
    Recently, I experienced a lengthy and debilitating bout of a winter virus and decided that I either consider my health as my priority or I probably would not survive another winter.
    As I also take full responsibility for my health and understand the law of attraction, it was not a surprise to me to find the internet stacked with Youtube Keto information when I started to search. One site led to another.
    But I was surprised to find Perfect Keto with its comprehensive knowledge and professional approach to this powerful health subject.
    I have, of course, not finished my reading (study) of your pages and did not know if this was the correct place to put a comment (sorry about the length of it).
    I simply wish to say a sincere thank you for helping me to transform my life (an ongoing process) by sharing your knowledge.
    My gratitude to the internet expands.

  12. Hello. I guess I have had the keto flu now for almost 3 weeks. I have never had body pain/soreness like this in my life! OMG! I will never cheat again. Hope it subsides soon.

  13. I started immediately hot/cold
    Aching all over. Sick to my stomach. Knee replacements ache.
    Chestheavy. Coughing
    Went to Dr she gave me antibiotic for viral flu.
    Starting reading more about the plan
    Yes Keto Flu

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