Hydration & electrolytes while fasting

What you usually drink

Plain still water, or sparkling water with nothing added, is the drink most people use through a daily window. Black coffee and tea with nothing in them are drinks you can add if you want them. An ordinary cup of either has almost no calories, which is why many people keep them in a fast that allows drinks and leaves out food. Coffee can still disturb sleep, worsen reflux, or leave your hands shaky. When a cup does any of those, leave it out for that day. How late the caffeine sits, and how milk or sugar turns tea into food, is covered in Tea while fasting.

Milk, juice, ordinary soda, sweetened drinks sold for fasting, coffee creamers, and a real cup of bone broth count as food, because they bring calories or enough substance to work as a small meal. Stirring a pinch of ordinary salt into water leaves you with salt and water. A mug of broth is closer to starting lunch. The longer list of what usually stays in the fasting hours, and what usually counts as food, is in What usually ends a fast.

When minerals come up

For a window of about 12 to 16 hours that starts after dinner and ends at the next meal, many people need nothing beyond the food in the eating hours and water while they wait. A headache in that range often comes from short sleep, from the first days without the coffee you usually drink in the morning, or from hunger that shows up at the clock time you normally eat. Those causes are common, so a headache on its own is a weak reason to start a mineral powder.

Once food has been missing for about a day, sweat in hot weather carries salt out and no meal is putting it back yet. Salt becomes a practical question at that point, and that stretch is covered in Water and minerals past a day. During an ordinary week of 16:8, where you still eat every day, some forums tell people to buy a tub of salts for a headache they call keto flu. Keto flu is the name those forums use for the headache, the tiredness, and the muscle cramps they blame on a gap in minerals. On a daily window that still includes a meal, the meal and a glass of water already cover what that tub is being sold to fix.

Potassium and magnesium show up in the same conversations as salt. While you still eat every day, they usually come from that meal, in ordinary food, rather than from a scoop of powder. Pills and powders bring a fixed amount, and that amount can interact with the kidneys and with some medicines. Pregnancy, breastfeeding, recovery from an eating disorder, diabetes, kidney disease, a heart-rhythm condition, and blood-pressure medicine each change how the body handles fluid and minerals. If any of those apply to you, talk with a clinician before you add a powder. The situations that need that conversation are in Who should be careful with fasting.

How to drink through the day

Drink water in smaller amounts across the day, instead of a large glass all at once. A large amount in one go can leave you feeling uncomfortably full. Drinking much more water than thirst is asking for can also dilute the sodium already in your blood, which is a separate problem from eating too little salt. Thirst, and urine that looks darker than usual, can suggest you need more water. The amount of sodium in your blood is something a blood test measures.

If you add salt, a pinch stirred into a glass of water is about what you might already use at the table. Pouring in more, because you hope the extra salt will make the fasting hours feel easier, is a larger amount, and extra sodium can raise blood pressure in people who are sensitive to it. A common question is whether that pinch should be pink Himalayan salt or Celtic salt. Which salt for a water fast? compares those with ordinary table salt. The color does not add a useful amount of other minerals, and there is still no amount to measure into each bottle.

Diet soda, flavored water, and a bottled drink whose label says electrolyte sometimes contain a sweetener or some calories along with the minerals. The ingredient list on the bottle is where that sweetener or calorie source shows up. If you find yourself wanting the next bottle the way you would want a snack, the drink is working as a flavored habit as well as a way to take in water.

Signs that mean stop

Dizziness when you stand up, confusion, fainting, chest pain, or weakness you cannot explain are reasons to stop the fast and get help, and adding more salt does not treat those signs. They are written out in When to stop a fast.

The fasting timer counts how many hours have passed, and the stage name on the screen changes because those hours changed. The clock cannot tell how much water you drank, and it cannot tell the sodium level in your blood.