People following the ketogenic diet may experience minor, short term symptoms, such as nausea, fatigue, and headaches. Some call this the keto flu.

Another name for the keto flu is keto induction, as these symptoms tend to occur when people start the diet. The symptoms develop when the body enters a state of ketosis, during which it burns fat for energy.

People can manage or prevent the keto flu by:

  • altering the types of fats that they eat
  • taking certain medications
  • consuming more fiber, vitamins and minerals, and water

In this article, we describe the keto flu and offer tips for preventing and managing these symptoms.

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Keto flu can cause a range of symptoms, including headaches and fatigue.

Keto flu refers to a set of symptoms that people may experience when they start the keto diet. These are usually minor and short term, lasting between a few days and weeks.

Symptoms of the keto flu include nausea, vomiting, headaches, and fatigue.

These symptoms arise as the body gets used to operating with fewer carbohydrates and as it enters a state of ketosis. The symptoms result from temporary imbalances in energy sources, insulin, and minerals in the body.

Why does keto flu happen?

Carbohydrates are the body’s main energy source. On the keto diet, a person reduces their carb intake to fewer than 50 grams (g) per day, compared with the recommended 200–300 g per day.

When the body does not take in enough carbs to use for energy, the liver begins to produce glucose for energy, using its stores. This process is called glucogenesis.

Eventually, the liver will not be able to produce enough glucose to keep up with the energy demands of the body.

The body will then start to break down fatty acids, which will produce ketone bodies, in a process called ketogenesis. Body tissues then use ketone bodies as fuel, and the body enters a state of ketosis.

The medical community considers nutritional ketosis to be safe for most people. However, people may experience symptoms.

The lack of carbohydrates decreases the amount of insulin in the bloodstream. As a result, people may experience an increase in the amount of sodium, potassium, and water that is released in the urine, which will cause dehydration.

Insulin is also involved in transporting glucose to the brain. Before the brain starts to use ketones for energy, it will have less fuel. This will occur for about the first 3 days of the diet before blood glucose returns to regular levels.

Symptoms may reduce as the body reaches a state of nutritional ketosis. This involves the blood concentration of a particular ketone body, called beta-hydroxybutyrate, being 0.5 millimoles per liter or more.

Symptoms of the keto flu are usually mild, begin when a person starts the diet, and may only last a few days to a few weeks. They may ease off when the body enters a state of ketosis.

According to one scientific profile of the diet, keto flu can involve the following symptoms:

Other researchers have reported additional symptoms, which usually peak between day 1 and 4 of the diet:

Additional short term symptoms, which tend to be preventable or easy to treat, include:

People on the keto diet may have bad breath. When the body has reached nutritional ketosis, the liver produces a ketone called acetone. Acetone enters the lungs, and it gives off a characteristic smell when a person exhales it.

Despite these symptoms, some researchers suggest that the keto diet can be beneficial for people with endocrine diseases, such as diabetes and obesity, or neurological diseases, including epilepsy.

Keto flu is not the same as ketoacidosis.

Ketoacidosis is a condition in which the body produces large numbers of ketone bodies. This causes the blood to become more acidic. Ketoacidosis can be a life threatening condition.

Typically, people on the keto diet do not have ketoacidosis.

The keto diet can help a person lose weight, but some people are put off by keto flu symptoms. These are temporary, and treatments and remedies can ease them.

The following strategies can help:

Eat different dietary fats

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Choosing certain fats, such as olive oil, can reduce the risk of keto flu symptoms.

If a person on the keto diet experiences abdominal symptoms, dietitians may recommend changing the types of fats in the diet.

High levels of medium chain triglycerides, from foods such as coconut oil, butter, and palm kernel oil, can cause cramps, diarrhea, and vomiting.

Eating fewer of these foods and more of those with long chain triglycerides, such as olive oil, may help prevent abdominal symptoms in people on the keto diet.

Take medications

Doctors may also prescribe histamine 2-receptor blockers or proton pump inhibitors to people who experience acid reflux.

Eat more fiber

People may have constipation or diarrhea when on the keto diet.

Dietitians may recommend eating more high fiber vegetables or taking fiber supplements to people with constipation. They may suggest taking carbohydrate free laxatives if these dietary changes are unsuccessful.

Drink more water

People on the keto diet may experience dehydration. If the person also has diarrhea, the risk of dehydration is higher.

Doctors recommend that people on the keto diet make sure to consume enough fluid and electrolytes to prevent dehydration.

Take supplements

One possible long term effect of the keto diet is vitamin and mineral deficiency. A doctor may suggest taking vitamin supplements to ensure that the body is receiving adequate amounts of calcium, vitamin D, zinc, and selenium.

Some people find that supplements for the keto diet can help reduce symptoms and promote the effects of the diet.

Manage diabetes

People with diabetes who follow a keto diet may experience episodes of low blood sugar, which doctors call hypoglycemia.

Before a person with diabetes begins a keto diet, they should consult a doctor. The doctor may need to modify insulin and oral drug dosages.

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A person with concerns about their symptoms should speak to a doctor.

If symptoms of the keto flu develop, it may not be necessary to consult a doctor. The symptoms are usually short term, minor, and easy to manage at home. However, doctors can recommend effective treatments.

They can also monitor a person’s condition and help prevent long term complications from developing. These may include:

Persistent nausea, vomiting, and abdominal pain may require medical attention. Anyone who is unsure whether their symptoms are to be expected should consult a doctor.

Before deciding to follow a keto diet, it is a good idea to consult a doctor to ensure that it is safe. This diet is not safe for everyone and can cause serious complications.

Doctors should frequently monitor cholesterol and fat levels in people on a keto diet, which can raise cholesterol levels. For this reason, it is important for people on the diet to let their doctors know.

People with fat metabolism disorders are at risk of coma or death if they fast or follow the keto diet.

Also, some medications, such as sodium-glucose cotransporter 2 inhibitors, can interact with the diet.

People with keto flu most commonly report abdominal symptoms, headaches, and fatigue.

Research suggests that the keto diet is safe and that the symptoms are usually minor and short term. However, doctors agree that the keto diet requires strict medical supervision to be effective for weight loss.

To minimize the risk of complications, people should start the diet slowly and gradually and visit their healthcare providers regularly. Also, dietitians can help with easing into the dietary changes.

Making certain dietary changes — including consuming plenty of fluids and electrolytes — can help manage symptoms of the keto flu.

Overall, it is important to remember that doctors are unsure about the possible long term health effects of the keto diet. Anyone following this diet should let their doctor know, so that they can monitor for any serious complications.