How to Avoid the Keto Flu (or Fix It Fast)

The 'keto flu' is not a real virus, but it feels like one. Headache, fatigue, muscle aches, irritability, brain fog, and difficulty concentrating typically peak on days 3–5 of a strict keto start. The good news: it is almost entirely preventable.

What causes it

As insulin drops, your kidneys dump sodium. As sodium leaves, potassium and water follow. The resulting electrolyte deficit — not the absence of carbs — is what makes you feel awful.

The prevention protocol (start on day 1)

1. Salt every meal generously. Aim for 3–5 g sodium/day total.
2. Drink 500 ml of broth with a pinch of extra salt each afternoon.
3. Take 400 mg magnesium glycinate at bedtime.
4. Eat an avocado or 2 cups of leafy greens daily for potassium.
5. Sleep 8 hours. Sleep deprivation dramatically worsens keto flu.

If you're already in it — the 24-hour fix

1. Morning: 500 mg sodium in 16 oz water. Repeat mid-morning.
2. Lunch: eggs, avocado, spinach, olive oil.
3. Afternoon: 500 ml salty bone broth.
4. Evening: 400 mg magnesium glycinate.
5. Nap or nap-adjacent activity — do not train hard.

When to worry

Mild flu lasts 1–5 days. If symptoms persist beyond a week, worsen severely, or include chest pain, shortness of breath, or fainting, contact a doctor.

The ease-in option

If you're keto-flu prone (or just hate feeling bad), phase in over 2–3 weeks: cut sugar first, then grains, then measure carbs. This gentler approach nearly eliminates keto flu.