The ketogenic diet has gained popularity as a natural way to lose weight and improve health.

The diet is very low in carbohydrates, high in fat and moderate in protein.

While the diet is considered safe for most people, it’s associated with some unpleasant side effects.

The keto flu, also called the carb flu, is a term coined by followers to describe the symptoms they experience when beginning the diet.

This article investigates what the keto flu is, why it happens and how to ease its symptoms.

Keto Flu Symptoms

The keto flu is a collection of symptoms experienced by some people when they first start the keto diet.

These symptoms, which can feel similar to the flu, are caused by the body adapting to a new diet consisting of very little carbohydrates.

Reducing your carb intake forces your body to burn ketones for energy instead of glucose.

Ketones are byproducts of fat breakdown and become the main fuel source when following a ketogenic diet.

Normally, fat is reserved as a secondary fuel source to use when glucose is not available.

This switch to burning fat for energy is called ketosis. It occurs during specific circumstances, including starvation and fasting ().

However, ketosis can also be reached by adopting a very low-carb diet.

In a ketogenic diet, carbohydrates are typically reduced to under 50 grams per day ().

This drastic reduction can come as a shock to the body and may cause withdrawal-like symptoms, similar to those experienced when weaning off an addictive substance like caffeine ().

Summary The keto flu is a term used to describe flu-like symptoms associated with beginning the very low-carb ketogenic diet.

Switching to a very low-carb diet is a major change, and your body may need time to adapt to this new way of eating.

For some people, this transition period can be especially difficult.

Signs of the keto flu may start popping up within the first few days of cutting back on carbs.

Symptoms can range from mild to severe and vary from person to person.

While some people may transition to a ketogenic diet without any side effects, others may experience one or more of the following symptoms ():

  • Nausea
  • Vomiting
  • Constipation
  • Diarrhea
  • Headache
  • Irritability
  • Weakness
  • Muscle cramps
  • Dizziness
  • Poor concentration
  • Stomach pain
  • Muscle soreness
  • Difficulty sleeping
  • Sugar cravings

These symptoms are commonly reported by those who have just begun the ketogenic diet and can be distressing.

Symptoms typically last about a week, though some people may experience them for a longer period of time.

While these side effects may cause some dieters to throw in the towel, there are ways to reduce them.

Summary When beginning a ketogenic diet, some people may experience symptoms, including diarrhea, fatigue, muscle soreness and sugar cravings.

The keto flu can make you feel miserable.

Luckily, there are ways to reduce its flu-like symptoms and help your body get through the transition period more easily.

Stay Hydrated

Drinking enough water is necessary for optimal health and can also help reduce symptoms.

A keto diet can cause you to rapidly shed water stores, increasing the risk of dehydration ().

This is because glycogen, the stored form of carbohydrates, binds to water in the body. When dietary carbohydrates are reduced, glycogen levels plummet and water is excreted from the body ().

Staying hydrated can help with symptoms like fatigue and muscle cramping ().

Replacing fluids is especially important when you are experiencing keto-flu-associated diarrhea, which can cause additional fluid loss ().

Avoid Strenuous Exercise

While exercise is important for staying healthy and keeping body weight in check, strenuous exercise should be avoided when experiencing keto-flu symptoms.

Fatigue, muscle cramps and stomach discomfort are common in the first week of following a ketogenic diet, so it may be a good idea to give your body a rest.

Activities like intense biking, running, weight lifting and strenuous workouts may have to be put on the back burner while your system adapts to new fuel sources.

While these types of exercise should be avoided if you are experiencing the keto flu, light activities like walking, yoga or leisurely biking may improve symptoms.

Replace Electrolytes

Replacing dietary electrolytes may help reduce keto-flu symptoms.

When following a ketogenic diet, levels of insulin, an important hormone that helps the body absorb glucose from the bloodstream, decrease.

When insulin levels decrease, the kidneys release excess sodium from the body ().

What’s more, the keto diet restricts many foods that are high in potassium, including fruits, beans and starchy vegetables.

Getting adequate amounts of these important nutrients is an excellent way to power through the adaptation period of the diet.

Salting food to taste and including potassium-rich, keto-friendly foods like green leafy vegetables and avocados are an excellent way to ensure you are maintaining a healthy balance of electrolytes.

These foods are also high in magnesium, which may help reduce muscle cramps, sleep issues and headaches ().

Get Adequate Sleep

Fatigue and irritability are common complaints of people who are adapting to a ketogenic diet.

Lack of sleep causes levels of the stress hormone cortisol to rise in the body, which can negatively impact mood and make keto-flu symptoms worse (, ).

If you are having a difficult time falling or staying asleep, try one of the following tips:

  • Reduce caffeine intake: Caffeine is a stimulant that may negatively impact sleep. If you drink caffeinated beverages, only do so in the morning so your sleep is not affected ().
  • Cut out ambient light: Shut off cell phones, computers and televisions in the bedroom to create a dark environment and promote restful sleep ().
  • Take a bath: Adding Epsom salt or lavender essential oil to your bath is a relaxing way to wind down and get ready for sleep ().
  • Get up early: Waking at the same time every day and avoiding oversleeping may help normalize your sleep patterns and improve sleep quality over time ().

Make Sure You Are Eating Enough Fat (and Carbs)

Transitioning to a very low-carb diet can cause you to crave foods that are restricted on the ketogenic diet, such as cookies, bread, pasta and bagels.

However, eating enough fat, the primary fuel source on the ketogenic diet, will help reduce cravings and keep you feeling satisfied.

In fact, research shows that low-carb diets help reduce cravings for sweets and high-carb foods ().

Those having a difficult time adapting to the ketogenic diet may have to eliminate carbohydrates gradually, rather than all at once.

Slowly cutting back on carbs, while increasing fat and protein in your diet, may help make the transition smoother and decrease keto-flu symptoms.

Summary You can combat the keto flu by staying hydrated, replacing electrolytes, getting plenty of sleep, avoiding strenuous activities, eating enough fat and cutting out carbs slowly over time.

People adapt to ketogenic diets differently. While some may experience weeks of keto-flu symptoms, others may adjust to the new diet with no adverse side effects.

The symptoms people experience are tied to how their bodies adjust to a new fuel source.

Usually, carbs provide the body with energy in the form of glucose.

When carbs are substantially reduced, the body burns ketones from fat instead of glucose.

Those who typically consume lots of carbs, especially refined carbs like pasta, sugary cereal and soda, may have a more difficult time when beginning the ketogenic diet.

Thus, the transition to a high-fat, very low-carb diet may be a struggle for some, while others are able to switch between fuel sources easily with little to no keto-flu symptoms.

The reason some people adapt to ketogenic diets easier than others is unknown, but genetics, electrolyte loss, dehydration and carbohydrate withdrawal are believed to be the driving forces behind the keto flu.

Luckily, the uncomfortable symptoms of the keto flu only last about a week for most people.

However, some people may have a more difficult time adapting to this high-fat, low-carb diet.

For these individuals, symptoms may last several weeks.

Fortunately, these symptoms will gradually decrease as your body gets used to converting ketones into energy.

While keto-flu symptoms are commonly reported by those shifting to a ketogenic diet, if you are feeling particularly unwell and experiencing symptoms like prolonged diarrhea, fever or vomiting, it’s best to contact your doctor to rule out other causes.

Summary Some people may experience keto-flu symptoms due to genetics, electrolyte loss, dehydration and carbohydrate withdrawal. The keto flu usually lasts for about a week, but some may experience symptoms for over a month.

Although the ketogenic diet may be helpful for many people, it’s not suitable for everyone.

For example, the ketogenic diet may not be appropriate for pregnant or breastfeeding women, children and teens, unless it’s being used therapeutically under medical supervision.

Furthermore, this diet should be avoided by those with certain health conditions like kidney disease, liver disease or pancreatic conditions.

Also, those with diabetes who are interested in following a ketogenic meal plan should consult their doctor to determine if this diet is safe and suitable for their specific needs.

Lastly, this diet may not be appropriate for individuals who are hypersensitive to dietary cholesterol, who account for around one-quarter of the world’s population ().

Summary The ketogenic diet may not be safe for pregnant women, children, people with kidney, liver or pancreatic disease and those who are sensitive to dietary cholesterol.

The keto flu is a collection of symptoms associated with the body adapting to a ketogenic diet.

Nausea, constipation, headaches, fatigue and sugar cravings are common in some people who are adapting to a high-fat, low-carb diet.

Staying hydrated, replacing lost electrolytes, getting enough rest and ensuring you are consuming proper amounts of fat and carbohydrates are ways to reduce keto-flu symptoms.