Electrolytes

Electrolytes do not break a fast. Sodium, potassium, and magnesium are minerals, not a source of calories, so taking them as plain electrolytes does not trigger digestion or raise insulin, and the fasted state continues uninterrupted.

Electrolytes are important during a fast because fasting actively depletes them. Insulin normally signals the kidneys to hold on to sodium, so when insulin falls during a fast, that signal weakens and the kidneys excrete more sodium and the water that follows it, carrying potassium and magnesium out along with it. This loss is a normal part of fasting, but it is often what produces the headaches, fatigue, muscle cramps, and lightheadedness people notice on longer fasts, sometimes called the keto flu, which is why electrolytes are commonly replenished during longer fasts.

Because they contain no calories, electrolytes are one of the few things that fit even a clean fast, alongside water, black coffee, plain tea, and certain non-caloric supplements. The main caveat is which form they are in: plain electrolytes are fast-safe, but many electrolyte and sports drinks add sugar, juice, or other sweeteners and the calories that come with them, which would break a fast. Reading the label for added calories is what separates a fast-safe electrolyte source from one that is not.