Water and minerals past a day

A daily window still has a meal

A 12 to 16 hour overnight gap is mostly water, then breakfast. Headaches in that range are often short sleep, the first days without the usual caffeine, or the habit of eating at that clock time. Hydration and electrolytes covers that daily window, including the ordinary week of 16:8 where no special mix is required.

Salt becomes the louder question once that meal has been missing for about a day. Heat and heavy sweat raise it further, because sweat carries salt out and there is still no meal putting it back. Two days of 16:8 are still food every day, with a meal between the fasting hours. That is a different situation from 36 or 48 hours with no meal at all.

Why salt comes up after the first day

In 1982, Peter R. Kerndt, James L. Naughton, Charles E. Driscoll, and David Loxterkamp reviewed fasting physiology in the Western Journal of Medicine. In the supervised fasts they describe, the quick drop on the scale in the first days is mostly salt and water leaving in the urine. Sodium lost in urine over the first week, in the cases they compare, was about 200 to 350 milliequivalents. A milliequivalent is a lab measure of how much sodium left in the urine. We are not turning that range into a grams-per-day target for a jar at home. Most of those studies were in people with obesity, in a clinic, so the same figure is a poor plan for someone leaner fasting at home. The early drop on the scale is also a poor guide to how much body fat you lost.

Kerndt and colleagues list complications that belong with this topic: blood pressure that falls when you stand, and disturbed heart rhythms. A dull headache, a muscle cramp, or lightheadedness that eases after you sit, drink water, and take a little salt, when a little salt is already your habit, is a pattern people report. That pattern does not show that a branded blend is required.

Potassium and magnesium come up in the same conversations. Food is where they usually come from while you are eating. Pills and powders have doses, and they interact with kidneys and with some medicines. If you take blood-pressure medicine or a water pill, or you have kidney disease or a heart-rhythm condition, ask the clinician who knows those medicines before you add a powder.

A vitamin or another supplement, beyond sodium, potassium, and magnesium, is a separate question. Do supplements help on a long water fast? takes that question up.

What to drink

Drink water through the day. Thirst can feel like hunger, especially around the time you usually eat. Plain still water, or sparkling water with no sweetener, is what staying hydrated means on this stretch. Sip, rather than drinking a large amount at once. A sudden load can leave you feeling overly full. Drinking far more water than thirst is asking for can also dilute the sodium in your blood, which is a separate problem from going without salt. Thirst and the color of urine are rough guides. They are not a blood test.

Black coffee and unsweetened tea are optional. They can still bother sleep, reflux, or anxiety, and coffee can make you pee more. If the mug makes you shaky, or more fixed on finding salt, skip it. Milk, sugar, and a tea latte are food, which Tea while fasting goes through. A bottle that says electrolyte on the label and also contains sugar, juice, or a sweetener may count as food by the rule you set for yourself.

A pinch of salt in water

A pinch of salt in water, or a cup of broth if your own rule already allows broth, is a small act. Pouring in more salt so the hours will feel easier is a different act. Extra sodium can raise blood pressure. Some blood-pressure pills hold onto potassium, and extra potassium on top of those pills, or on top of kidneys that do not clear it well, can be dangerous. The amount that is safe depends on the person, the kidneys, and the medicines. We are not listing scoops.

People ask whether that pinch should be pink Himalayan salt or Celtic salt, and how much to put in each bottle. Which salt for a water fast? compares those brands with ordinary table salt. The color does not turn the pinch into a supplement, and there is still no amount per bottle.

Forums sell a quieter 36 hours as a kit: a branded fasting salt, a homemade mix under names like snake juice, potassium powder, and magnesium at a round number because a chart said so. The same shop shows up on ordinary days in What does not make it easier. Adding more hours does not turn that kit into a safer method. It remains something you bought. Supervised clinics sometimes add a little salt or broth and check blood tests, because a person is there to watch and to stop the fast. Copying a hospital mix from memory, or changing a prescription because a thread did, skips that person.

When feeling unwell means stop

Dizziness when you stand up, confusion, fainting, chest pain, a heartbeat that feels racing or irregular, or weakness you cannot explain means stop. Eat, if you can do that safely, and get help. More salt does not fix that list. The signs are written out in When to stop a fast. Hour 36, or any other round number, does not outrank them. The stage name on the timer follows how many hours have passed. It does not measure the sodium in your blood.

If the stretch you already have in mind runs past 72 hours, a week, or longer, take the mineral question to a clinician. If you already mean many days is written for that length.

What the timer is doing

The fasting timer counts elapsed hours. The 24h, 36h, and 48h buttons are one continuous stretch. Open is the button with no target finish: it counts until you press End Fast. Those buttons exist so a longer fast is not stuck behind a paywall. Feeling unwell still means you stop. A salt mix is still a separate purchase.

Start the clock when you stop taking calories by your own rule. Keep water nearby. Press End Fast when you eat, including when you eat earlier than you planned, and when you should stop. If you are still choosing the first day of a daily window, begin with How to start fasting.

What those hours often feel like once the first day is over, and which of those feelings mean stop, is in After the first day.