Keto Electrolyte Calculator.

Insulin does more than move glucose. One of its quieter jobs is telling the kidney to hold on to sodium. Cut carbohydrate far enough and insulin falls, the signal to retain sodium weakens, and the kidney starts letting it go, taking water out with it. That is why the scale drops several pounds in the first week of keto and why the drop is not fat.

During a fast the same mechanism runs harder. Low insulin and rising glucagon push the liver to make ketones, and ketones are anions: they cannot leave the body alone, so they leave paired with a positively charged partner, and early in a fast that partner is largely sodium. Physiologists have a name for it, the natriuresis of fasting, and it has been described in the literature since the 1970s. Ammonium takes over the job later, which is part of why the effect eases after the first days.

This is the honest reason a keto or fasting electrolyte target is higher than a general population one. It is not a supplement-industry invention. It is what happens when the hormone that tells your kidney to keep salt stops being secreted.

Headache, fatigue, light-headedness when you stand up, muscle cramps, and feeling like your training has fallen off a cliff. Those are the classic first-fortnight complaints, and most of them are the symptoms of a contracted blood volume rather than anything to do with ketones themselves. Correcting sodium often resolves them within a day, which is a strong clue about the cause.

The claim worth resisting is the stronger one, that every symptom in the first weeks is electrolytes and can be salted away. Feeling flat is common and usually fixable. Feeling genuinely unwell is not the same thing, and persistent palpitations, confusion, fainting or severe cramps deserve a clinician rather than another spoon of salt.

SGLT2 inhibitors, the diabetes and heart-failure drugs whose names end in -flozin, work by making the kidney dump glucose into the urine. Combine that with a ketogenic diet or a fast and the body can slide into ketoacidosis while blood glucose still reads normal or only slightly high. It has a name, euglycemic diabetic ketoacidosis, and there are published case series of it happening specifically to people who started keto or intermittent fasting on one of these drugs.

What makes it dangerous is the reassurance. The number most people check to decide whether something is wrong, blood glucose, stays unremarkable, so the picture gets dismissed and treatment is delayed. A ketone reading looks like deep ketosis rather than an emergency, and a ratio like GKI cannot separate the two at all, because both numbers move in the direction that looks like success.

This is why the calculator asks about these drugs before it shows anything. If you take one, the question is not how much sodium to take. It is whether to fast at all without talking to the person who prescribed it, and whether the drug should be paused first.

Sodium and magnesium are forgiving in healthy people: overshoot and you get thirst or loose stools. Potassium is not like that. Blood potassium that runs too high interferes with cardiac conduction and can be fatal, and the body clears the excess through the kidney, so anything that impairs the kidney or blocks the hormonal pathway that drives potassium excretion changes the arithmetic completely.

That is why this calculator asks about kidney disease, ACE inhibitors, ARBs and potassium-sparing diuretics before it will show a potassium figure, and why the number it does show is the ordinary dietary reference intake rather than a supplement dose. Oral potassium tablets are limited to 99 mg in the United States precisely because larger single doses have caused harm. Clinical ketogenic programmes give the same advice: get potassium from vegetables, avocado and broth, not from a bottle.

One consequence worth stating plainly: during a water fast you cannot reach a potassium target from food, because you are not eating. That is a genuine argument for keeping unsupervised fasts short rather than for improvising with supplements.