HOME / GUIDES / HEADACHES WHILE FASTING
It is usually salt, not hunger. Fasting lowers insulin, your kidneys release sodium and water, and a headache follows the loss.
The fix takes about twenty minutes and does not break your fast. Drinking more plain water on its own can make it worse.
The mechanism
The extra trips to the bathroom during a fast and the headache that follows them are the same event.
What to do
None of the first three break a fast. Work down the list and give each one twenty minutes before moving on.
A pinch of good quality salt in a large glass. This is the single most effective step.
Salted broth or an electrolyte mix without calories does the same job more comfortably. Both keep the fast intact.
If you normally drink coffee and have not had one, this may be caffeine withdrawal rather than the fast. Black coffee does not break a fast.
If it is still there after thirty minutes, eat. A finished fast is worth more than a miserable one, and Burn records the length you actually reached.
In the app
Burn logs sodium, potassium and magnesium next to your water, so the salt you added at hour 14 is a record rather than a vague memory of a rough afternoon. The symptom check sits one tap from the timer for the moment itself.
Log sodium, potassium and magnesium next to your water, against targets you set. A rough week leaves a record rather than a vague memory.
Notifications through the fasting hours, rate-limited and aware of your quiet hours.
WHEN TO STOP
End the fast and eat if the headache is severe, comes with vision changes, or arrives alongside dizziness that does not settle, heart palpitations or shaking. Those belong in a different category from ordinary fasting discomfort, and are worth raising with a doctor if they repeat.
Anyone managing blood pressure, kidney function, or heart medication should get advice before adding salt or supplements.
Read the safety guidance →The link between lower insulin, sodium excretion and fluid loss during fasting is well described, as is the role of low sodium in headaches. Claims here are drawn from peer-reviewed research and traced in our evidence policy. No dose is published, because needs shift with fast length, training, heat and your own health.
Burn logs what you enter and names the stage the clock has reached. It does not measure your electrolyte status, ketosis, autophagy, or metabolic state, and the symptom check is guidance rather than a diagnosis.
Burn's symptom check, hunger timer and four more tools sit one tap from the timer, with water and minerals logged alongside every fast.
Download free on the App StoreiPhone, iPad, and Apple Watch. Requires iOS 18 or watchOS 11.
