The Keto Flu: How to Treat and Manage Symptoms

Whether your goal is to lose weight, manage symptoms of diabetes, PCOS, or another health condition, or you just want more energy to get through daily life, you’ve decided the ketogenic diet may be the solution. You’re eating the right macros (75% fat | 20% protein | 5% carbohydrates), you’re losing weight, you’re feeling energized… then you suddenly feel sick. 

Don’t worry. You’re probably experiencing the Keto Flu.

What is the Keto Flu?

When starting the ketogenic diet, you may experience the Keto Flu as your body transitions from carb-burning mode to fat-burning mode. This typically happens several days after you start eating a low-carb, high-fat diet, and symptoms could last one to two weeks. The symptoms are similar to the flu, hence the name. It’s not contagious or dangerous, but it is unpleasant.

The discomfort that you’re feeling is a natural reaction your body goes through when it transitions from burning glucose to burning fatty acids (ketones) for fuel. Fat is your body’s secondary fuel source behind carbohydrates (in the form of glucose). You will naturally burn fat when there’s not enough glucose in your diet. Once your body has switched over to burning fat, you have officially entered ketosis.

What are the symptoms of the Keto Flu?

If you already eat a diet that’s relatively low in processed sugars and starches, you may notice only mild symptoms, or none at all. But if you’re switching from a highly processed, high-sugar diet, you may be more likely to experience “withdrawal” symptoms.

Here are some common Keto Flu symptoms you may experience:

  • Fatigue
  • Headaches
  • Brain fog
  • Low energy
  • Poor concentration
  • Irritability
  • Weakness
  • Nausea
  • Dizziness
  • Muscle soreness or cramps
  • Insomnia
  • Diarrhea
  • Constipation
  • Vomiting
  • Food cravings


If you’ve been eating the typical Standard American Diet (SAD), you’re likely used to eating 250 – 350g of carbohydrates, including sugar, every day. When you adopt a ketogenic diet, you’re slashing your carb intake to just 25-50g per day. 

Most Americans now consume so much refined sugar and processed carbs that they are “metabolically rewired” to burn sugar for energy and store the excess as fat. Breaking this cycle can throw your body out of balance and cause temporary fatigue and flu-like systems.

Feeling these symptoms means you’re on the right track and your body is transitioning into a state of ketosis, which is when it starts burning fat for fuel. Don’t let these symptoms make you turn back to carbs or give up on the keto diet. 

What causes the Keto Flu?

While there is no scientific consensus on what causes the Keto Flu, here are some of the most common theories.

#1 Keto Flu Cause: Electrolyte Deficiency

This is the most widely accepted culprit because Keto Flu symptoms are usually minimized or eliminated when electrolytes are replenished. A popular source of electrolytes for keto dieters is beta-hydroxybutyrate (BHB).

When your body uses glycogen to fuel itself, it uses water for this metabolic process. When you stop using glycogen for fuel, your body sheds water (via urination), and electrolytes go with it. Electrolytes such as magnesium, calcium, sodium, and potassium are crucial for your body to operate efficiently. 

When you have an electrolyte imbalance or deficiency, you can experience flu-like symptoms. You can also experience similar symptoms after an intense workout that involves excessive sweating. 

#2 Keto Flu Cause: Fat Adaptation

During the period of time between starting a low-carb diet and achieving ketosis, you’re in what’s referred to as the “fat adaption stage.” That’s because your body is adapting to using fat for energy. Because you’ve drastically cut carbs to 5% of your calories, your body doesn’t have enough carbohydrates to use as fuel anymore. However, it hasn’t yet learned to use all the fat you’re consuming as fuel. In the interim, your body uses something called “muscle glycogen,” which are your glucose stores. 

Some research suggests that reduced muscle glycogen (because your body is using it for energy) may cause lethargy and mood swings. 

#3 Keto Flu Cause: Reduced Insulin Levels

Insulin is a hormone that helps your body absorb glucose from your bloodstream. When you have less glucose in your system, you don’t need as much insulin to process it (i.e. to lower your blood sugar levels).

That’s why when you switch from a high-carb diet to a low-carb diet, your insulin levels usually drop drastically.

Lower insulin levels is good for your health. In fact, it’s one of the main reasons the ketogenic diet is so beneficial. People often notice improved cognitive function, more energy, stabilized blood sugar, fewer seizures, and much more.

When glucose is no longer available as an energy source and your insulin levels are very low, your liver starts converting fat into ketones. Most of your cells can use these ketones in place of glucose for energy. Once your body is mainly using ketones and fat for energy, you’ve entered ketosis. You can use monitors or testing strips to determine whether or not you’re in ketosis.

It can take time for your brain and some of your other organs to adjust to using this new fuel source. When your insulin levels drop, your body reacts by ridding itself of excess water and sodium (which bind themselves to the glycogen in your system). This explains why you may urinate more often in the first week after starting the keto diet (and may lead to the electrolyte imbalances mentioned above). This also explains the fast weight loss (the “whoosh”) that often occurs in the early stages of the diet; you’re mostly losing water weight due to lower sodium levels.

What’s the best way to treat Keto Flu symptoms?

Most of the symptoms of the Keto Flu can be minimized or eliminated with a few simple steps.

1. Drink extra water

Staying hydrated is essential. Drink more water than you normally do. Hydration can relieve fatigue, headaches, and muscle cramps. Replacing fluids is particularly important if you experience diarrhea, which can dehydrate you quickly.

2. Replenish electrolytes

Supplementing with electrolytes is important for those new to the keto diet. You can also replenish some electrolytes and other essential micronutrients through food:

  • Potassium: avocados, nuts, dark leafy greens (spinach, kale), salmon, plain full-fat yogurt, and mushrooms
  • Magnesium: nuts, dark chocolate, artichokes, fish, and spinach
  • Sodium: salt, soup broth, bacon, pickles, and sauerkraut
  • Calcium: cheese, yogurt, leafy greens, broccoli, seafood (sardines), and almonds
  • Phosphorus: meats, cheese, nuts, seeds, and dark chocolate
  • Chloride: most vegetables, olives, seaweed, and salt

You can also drink coconut water for electrolytes. Just be aware that some brands of coconut water contain added sugar, so check the nutrition facts.

3. Eat more calories 

If you’re feeling nauseous or vomiting, you probably don’t have much of an appetite. Ironically, not eating enough could be causing you to feel nauseous. Try to consume as many keto-approved foods as you can, and graze on healthy low-carb snacks to help increase your daily caloric intake.

Add as many of these fat sources to your meals as you can:

  • Coconut oil
  • MCT oil
  • Lard
  • Macadamia, olive, or avocado oil
  • Ghee or butter 
  • Tallow 

4. Cut carbs gradually

If you’re having a tough time adapting to the ketogenic diet, you may have to eliminate carbs gradually instead of all at once.

Instead of immediately dropping to 25g of carbs per day, try cutting back to 100g for a few days, then 75g, then 50g. Slowly increase your fat intake each day as well.

As you slowly reduce carbs, choose healthier carbs like fruits and vegetables instead of pasta and rice. Avoid processed foods (like crackers and cereal) as much as possible.

5. Take a break from exercising

It’s okay to take a break from exercising or do more gentle workouts during this time. Instead of running, do a 30-minute walk. Instead of weight lifting, try yoga or stretching. Listen to your body and gradually increase your exercise intensity over time when you feel better and have more energy.

6. Get more sleep

Insufficient sleep can add to your body’s stress and exacerbate the Keto Flu symptoms, so make sure you’re getting 7 to 9 hours of sleep a night. 

If you’re having trouble falling or staying asleep, try one or all of the following tactics:

  • Epsom salt baths
  • Herbal tea
  • A break from electronics 2 hours before bed
  • Yoga
  • Meditation

7. Take exogenous ketones

Consuming exogenous ketones can help manage Keto Flu symptoms. Beta-hydroxybutyrate are ketone salts that contain high levels of potassium, magnesium, sodium, and calcium (the four cornerstone electrolytes your body needs to function properly). In addition to replenishing your electrolytes, the BHB can help you achieve or maintain a state of ketosis.

The Keto Flu is a good sign

The Keto Flu is a good indication you’re doing the keto diet correctly and are on your way to achieving ketosis. If you happen to experience any of the symptoms, know that they’re temporary. Stay the course and push through this phase because once you get past it, that’s when you’ll experience the many benefits of the keto diet, including weight loss, increased energy, better mental focus, and more restful sleep. The keto diet has also been shown to be beneficial for those who want to better manage the symptoms of type 2 diabetes, epilepsy, obesity, or PCOS.

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