Electrolytes while fasting: the trick to not feeling dizzy
Headaches, dizziness and fatigue while fasting are almost always low sodium. How to replace electrolytes without breaking your fast.
Part of the complete guide What breaks a fast (and what doesn't)
What the science saysElectrolytes for fasting: which to take and how
Fasting lowers insulin and your kidneys flush out more sodium and water (the natriuresis of fasting), which explains much of the headache, dizziness and fatigue of the first hours and days. Sodium, potassium and magnesium without sugar have no calories and do not break your fast; on fasts over 18-24 hours, or with heavy sweating, a pinch of salt in your water is usually enough.
- Insulin drives sodium reabsorption in the kidney; its fall explains the natriuresis of fasting and sodium retention on refeeding (DeFronzo 1981). [1]
- Renin, aldosterone and glucagon all play a role in the natriuresis of fasting (Spark 1975). [2]
- Headache, insomnia, hunger and metabolic acidosis were the adverse effects reported in prolonged fasting trials (Ezpeleta 2024). [3]
Why they matter so much
When you fast, insulin drops and your kidneys flush out more sodium and water. That electrolyte loss is the number one cause of feeling bad while fasting: headaches, dizziness, cramps, fatigue and brain fog. It is not the fast: it is the missing salt.
The 3 key electrolytes
- Sodium: the big one. A pinch of salt in your water works wonders.
- Potassium: helps with cramps and energy.
- Magnesium: improves sleep, cramps and digestion.
How to take them without breaking your fast
Pure electrolytes have no calories, so they do not break your fast. Your options:
- A pinch of salt (table or Himalayan) in your water.
- Electrolyte supplements with no sugar or caloric sweeteners.
- Sparkling water with a pinch of salt and a squeeze of lemon.
Skip commercial sports drinks: they are loaded with sugar and break your fast.
When you need them most
On long fasts (18 h+), if you are training and sweating, or if you feel dizzy standing up. On a normal 16/8 with good hydration you may not need them at all, but a pinch of salt never hurts when you are feeling flat.
How Ayúname helps
Ayúname reminds you to hydrate during your fast. Combine that with a pinch of salt and you will reach the end of your window with energy and no headache.
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Frequently asked questions
Do electrolytes break a fast?
What can I take so I do not feel dizzy while fasting?
Scientific sources (3)
- The effect of insulin on renal sodium metabolism. Diabetologia, 1981.
- Renin, Aldosterone and Glucagon in the Natriuresis of Fasting. New England Journal of Medicine, 1975.
- Efficacy and safety of prolonged water fasting: a narrative review of human trials. Nutrition Reviews, 2024.