What Is Keto Flu?
Keto flu is the cluster of temporary symptoms — fatigue, headache, irritability, brain fog, and muscle cramps — that many people feel during the first one to two weeks of starting a ketogenic diet, while the body adapts to burning fat for fuel.
When you drastically cut carbohydrates, your body sheds water and electrolytes (sodium, potassium, magnesium) along with depleted glycogen stores — and that shift is what produces the flu-like symptoms. The good news is that keto flu is short-lived: most people feel back to normal within a week or two as their metabolism adapts to running on fat and ketones. Drinking enough water, salting food liberally, and supplementing electrolytes are the most effective ways to minimize symptoms during the adjustment period.