Keto flu
The first days of keto can feel like a flu: headache, fatigue, irritability. It's temporary, it has an explanation — and above all, it has a fix.
What it is and why it happens
When you cut carbs, insulin drops and your kidneys release a lot of water and sodium within days. That rapid loss of fluid and electrolytes — not the lack of carbs — is the main driver of the symptoms while your body switches fuel.
Typical symptoms
Headache
Fatigue / low energy
Brain fog
Irritability
Dizziness
Mild nausea
Muscle cramps
Poor sleep
It usually starts on day 1-3 and lasts 2 to 7 days. Managed well with electrolytes, many people barely feel it.
How to fix it fast
- Salt and water: add 1-2 g of extra sodium per day (broth, salting your food). It's remedy #1.
- Cover potassium and magnesium with food: avocado, spinach, salmon, seeds.
- Drink more water than usual (with the salt, not on its own).
- Eat more fat: if you're hungry or tired, cutting calories is not the answer.
- Sleep well and dial down workout intensity for a few days.
- Patience: the symptoms disappear once your body adapts.
How to prevent it
- Start electrolytes on DAY 1 — don't wait for symptoms.
- Don't cut calories at the same time as carbs during week one.
- Hydrate more than usual from the start.
- Coming from a high-sugar diet? Step down in two stages (a week at 50 g, then 20-25 g).
Informational content, not medical advice. If symptoms are severe or last more than a week, see a healthcare professional.
