What is the keto flu?
The term 'keto flu' refers to a temporary state experienced by some people as their bodies adapt to a ketogenic diet. This occurs when the body switches its primary fuel source from glucose (from carbohydrates) to ketones (from fat). This metabolic transition is known as nutritional ketosis. For individuals accustomed to a high-carbohydrate diet, this shift can shock the system, causing withdrawal-like symptoms.
Symptoms typically appear within the first few days and can range from mild to severe, varying greatly from person to person. The most common symptoms include headaches, fatigue, nausea, irritability, and muscle cramps. Some individuals also report feeling 'feverish' or experiencing chills.
Can a keto diet cause a true fever?
A ketogenic diet itself does not cause a true fever. A fever is an elevated body temperature that is part of the body's immune response to an infection, such as a virus or bacteria. The flu-like symptoms of keto flu are a reaction to the dietary change, not an infection. However, a person starting a keto diet could coincidentally contract a real illness, in which case a fever would be a symptom of that separate infection.
Harvard Health emphasizes that while the keto flu is a real phenomenon, it is not the same as a viral illness and should not cause a high, debilitating fever. If a person experiences a persistent or high fever, it is crucial to consult a doctor to rule out other medical causes.
Key physiological causes of fever-like symptoms
Understanding the specific physiological changes that occur during the transition to ketosis can help explain why many people feel unwell.
Dehydration and water loss
When you drastically cut carbohydrates, your body depletes its glycogen stores. Glycogen binds to a significant amount of water in the body. As these stores are used up, the excess water is flushed out through urination. This rapid water loss can lead to dehydration, which is often a cause of symptoms like fatigue and headaches. Dehydration can also cause an increase in body temperature, which might feel like a low-grade fever.
Electrolyte imbalances
This rapid flushing of water also causes a loss of key electrolytes, including sodium, potassium, and magnesium. A ketogenic diet naturally restricts many foods that are rich in these minerals, such as fruits and starchy vegetables. These imbalances can trigger a range of symptoms that contribute to the 'flu-like' feeling, such as muscle cramps, weakness, and fatigue.
Carb withdrawal
For many people, cutting out refined carbohydrates and sugar is a significant change. Sugar has addictive properties, and withdrawing from it can lead to symptoms similar to detoxification. This can manifest as headaches, cravings, irritability, and overall malaise that is easily mistaken for a viral illness.
Comparison: keto flu, viral flu, and diabetic ketoacidosis
To better understand the differences, here is a comparison of these three conditions:
| Feature | Keto Flu | Viral Flu (Influenza) | Diabetic Ketoacidosis (DKA) |
|---|---|---|---|
| Cause | Body adapting to low-carb diet, carb withdrawal, dehydration, and electrolyte imbalance. | Viral infection (e.g., influenza virus). | Severe lack of insulin leading to a dangerous buildup of ketones and blood acid; life-threatening. |
| Symptoms | Fatigue, headache, nausea, muscle cramps, dizziness, irritability, brain fog, chills or feeling feverish. | Fever, cough, sore throat, muscle aches, runny nose, fatigue. | High blood sugar, fruity-smelling breath, extreme thirst, frequent urination, nausea, vomiting, abdominal pain, confusion. |
| Fever | Not a true fever caused by infection, but can cause a subjective feeling of being feverish or chills. | Typically involves a measurable, elevated body temperature. | Can occur, often as a symptom of a triggering infection. |
| Duration | Usually a few days, but can last several weeks for some. | Typically lasts about a week. | Requires immediate medical attention and treatment. |
| Who it affects | People transitioning to a ketogenic diet. | Anyone exposed to the flu virus. | Primarily people with type 1 diabetes, though can occur in type 2 diabetes under certain circumstances. |
How to manage and prevent keto flu symptoms
To ease the transition and minimize the risk of experiencing severe symptoms, including feeling feverish, consider the following steps:
- Stay hydrated: Drink plenty of water throughout the day, as dehydration is a major contributor to keto flu symptoms.
- Replenish electrolytes: Replenish minerals lost through increased urination. Options include bone broth, adding extra salt to your food, or using a sugar-free electrolyte supplement.
- Increase fat intake: Ensure you are consuming enough healthy fats to fuel your body and satisfy hunger, which can help mitigate low energy levels.
- Ease into it: Instead of an abrupt change, gradually reduce your carbohydrate intake over a week or two to lessen the shock to your system.
- Get enough rest: Prioritize sleep and avoid strenuous exercise in the initial adaptation phase. Light activities like walking or yoga are better options.
Conclusion
While the answer to can keto cause fever? is technically no, the feeling of being feverish is a valid and common part of the temporary metabolic shift known as the 'keto flu'. The discomfort is a result of dehydration, electrolyte imbalance, and carb withdrawal, not an infection. By managing hydration, replenishing electrolytes, and giving your body time to adapt, these symptoms can be minimized or avoided entirely. If you experience a persistent or high fever, it is critical to seek medical advice to ensure there is no underlying illness. The initial hump can be challenging, but for many, it is a manageable part of the journey toward a ketogenic lifestyle.
Visit Healthline for more detailed information on keto flu symptoms and management.
