Fasting and electrolytes: why 'no sugar' on the label doesn't mean what you think

Fasting and low-carb diets have moved from niche to mainstream. They also do something to your electrolyte balance that almost nobody warns you about, and most products marketed at this exact audience are quietly designed to break the diet they're sold to support.

Why low carb increases sodium loss

When you cut carbs aggressively — keto, low-carb, or any fasting protocol over 16 hours — your insulin levels drop. Insulin is one of the main signals that tells your kidneys to retain sodium. When insulin falls, your kidneys do the opposite: they excrete sodium more readily.

This is why people often feel terrible in the first week of keto. The "keto flu" — headache, fatigue, dizziness, muscle cramps, brain fog — isn't carbohydrate withdrawal. It's an electrolyte depletion event, primarily sodium, with potassium and magnesium close behind.

The fasting variant

Extended fasts (24+ hours) hit the same lever. Without food coming in, insulin stays low. Without insulin, sodium and water leave faster than they would on a normal eating pattern. Without sodium, you cannot hold water — so you also dehydrate faster than you'd expect from "just not eating."

This is why experienced fasters drink salt water, broth, or electrolyte sticks. It's not about flavour or "feeling like you're consuming something" — it's about not crashing.

The maltodextrin problem

Many "zero-sugar" or "keto-friendly" electrolyte sachets contain maltodextrin as a flow agent or filler. The amount is usually small — under 1 gram — but it's enough to spike insulin in a sensitive faster, which directly defeats the purpose of being in a fasted state.

If you're fasting for autophagy, metabolic flexibility, or insulin sensitivity, a maltodextrin-containing electrolyte stick is silently breaking your fast. The label doesn't say "sugar," but your pancreas can't read the marketing copy.

What to actually look for

If you're using electrolytes for fasting or low-carb support, the back of the label should be short. Sodium, potassium, magnesium, citric acid for taste, a natural flavour, and a non-glycemic sweetener (stevia, monk fruit) if any. That's it.

No maltodextrin. No dextrose. No "natural cane sugar." No "rice flour" filler. No "modified food starch."

Repleo is built specifically with this audience in mind. Zero sugars of any kind. Zero maltodextrin. The carbohydrate count on the back of the pack is genuinely zero, not "rounded down from 0.9."

Dosing during a fast

For a 24-hour fast, a useful baseline is two electrolyte sticks plus 2–3 litres of water across the day. Salt your water if it tastes flat — your taste perception of salt actually changes during a fast, and what feels "too salty" on day one of a fast is often exactly what your body needs.

For longer fasts, consult a clinician. The principle stays the same: electrolytes are not optional during prolonged caloric restriction, they are the difference between feeling functional and feeling unwell.