Keto flu: why it happens and how to end it in 48 hours

"Keto flu" is a classic beginner problem: on days 2–5 you get headache, fatigue, irritability, muscle weakness and disturbed sleep. It is NOT flu and NOT a reaction to fat — it is electrolyte depletion, and it resolves within 24–48 hours with the right protocol.

What is actually happening

As insulin drops in the first days of keto, kidneys stop holding sodium and dump water — 3–4 g of water per gram of glycogen. Two kilos of fluid can go in 48 hours, taking sodium, potassium and magnesium with it (Bostock et al., Front Nutr 2020). Headache and cramps are electrolyte loss, not ketosis.

The classic protocol

• Sodium: 3–5 g/day extra (½ tsp salt in a glass of water 3× daily)
• Potassium: 3000–4000 mg/day (avocado, spinach, salmon, pumpkin seeds)
• Magnesium: 400 mg/day glycinate or malate (not oxide)
• Water: 2.5–3 L, but NOT over 4 L — it worsens sodium loss
• Broth: 300–500 ml/day — fastest source of all three

How long it lasts

With electrolytes: 24–48 hours. Without: 5–10 days, mislabelled "adaptation". If symptoms last over 7 days, check serum potassium and magnesium.

Higher-risk groups

• Women during menstruation
• Heavy exercisers (extra sweat losses)
• People on diuretics (talk to your doctor first)
• Renal failure — never add potassium without supervision

Prevention

Add sodium and magnesium a day BEFORE starting keto. Pick a first week without critical meetings — concentration dips slightly even with proper electrolytes.