The Science of Electrolytes

The SGLT1 transporter in your small intestine moves sodium and glucose together across the intestinal wall. This cotransport mechanism creates a localized osmotic gradient that pulls water along with it, and intestinal perfusion studies show substantially higher water absorption for glucose-sodium solutions than sodium alone. It's the reason oral rehydration solutions always contain sugar.

The osmolarity of an electrolyte drink relative to blood influences how fluid moves across the gut. Hypotonic solutions (under ~275 mOsm/L) often support faster net fluid absorption in study settings. Isotonic solutions (~275-295 mOsm/L) match blood concentration. Hypertonic solutions (above ~295 mOsm/L) can pull water into the gut before absorption.

Sodium constitutes over 90% of electrolyte losses in sweat. The average liter of sweat contains 900mg of sodium but only 200mg of potassium and 12mg of magnesium. Individual variation is enormous — sweat sodium concentration ranges from 200mg/L to over 1,600mg/L based on genetics, fitness, heat acclimatization, and diet.

Magnesium bioavailability varies meaningfully by form. Soluble organic and chelated forms such as citrate, glycinate, malate, and taurate tend to have better absorption evidence and GI tolerance than oxide. Magnesium oxide is cheap and dense, but less soluble and generally less bioavailable. For Lyte Lab, the form mainly affects label matching, grams required, taste, cost, and GI-tolerance tradeoffs.

Potassium is the dominant intracellular cation — 98% of body potassium is inside cells, with only 2% in the blood. This tight regulation means even small changes in blood potassium can be dangerous. Supplementation is safe for healthy individuals but requires more caution than sodium or magnesium.

Healthy kidneys regulate electrolyte balance with extraordinary precision, filtering 180 liters of blood per day and adjusting sodium, potassium, and magnesium excretion in real time. This is why healthy people can tolerate wide variations in sodium intake without harm — and why kidney disease fundamentally changes the equation.