Electrolyte Mixes

The small 5 g dextrose dose is not here for energy. It exists to activate the SGLT-1 (sodium-glucose linked transporter 1) in the intestinal wall. SGLT-1 co-transports sodium and glucose together — each glucose molecule transported pulls two sodium ions and water with it. Without a glucose stimulus, sodium absorption depends primarily on passive paracellular transport, which is significantly slower. At 5 g per 500 mL, this is a sub-physiological glucose dose (far below the level that would meaningfully contribute to carbohydrate fueling) but sufficient to saturate enough SGLT-1 transporters to meaningfully accelerate sodium uptake. This is the same mechanism that underlies oral rehydration solution (ORS) design.

The primary sodium source, contributing approximately 335 mg sodium per serving. Sodium citrate is preferred over pure sodium chloride at these doses for palatability — at 500 mg sodium total, a pure NaCl approach would produce a distinctly salty, brine-like beverage that is difficult to drink in volume during exercise. Citrate-based sodium has a milder, slightly tart character that remains palatable. It also functions as an alkalising buffer, contributing to a more comfortable beverage pH. The citrate anion is also well-absorbed and metabolised via the Krebs cycle.

Contributes approximately 150 mg sodium alongside the chloride anion. Chloride is the primary extracellular anion and is lost alongside sodium in sweat. Replacing chloride alongside sodium is important for maintaining plasma electroneutrality and supporting gastric acid production. The split between citrate and chloride sources (335 mg + 150 mg = ~485 mg from salts) achieves the ~500 mg target while keeping chloride concentration within normal physiological replacement ranges.

Contributes ~100 mg potassium. Potassium is the primary intracellular cation, and sweat losses range from 150–500 mg/L. Acute potassium depletion during a single exercise session is uncommon in healthy athletes eating a normal diet, but chronic under-replacement in high-training-load athletes can contribute to muscle dysfunction and fatigue. At 100 mg per 500 mL serving, this formula delivers approximately 20–65% of typical sweat potassium losses per 500 mL consumed — a meaningful contribution when multiple servings are taken across a long event.

Delivers approximately 25 mg elemental magnesium per serving. Exercise increases urinary magnesium excretion and marginal magnesium deficiency is disproportionately common in endurance athletes, contributing to reduced enzyme activity involved in glycolysis and muscle contraction. Citrate is the preferred magnesium form: magnesium oxide has poor bioavailability (~4% absorption), while magnesium sulphate (Epsom salt) is an effective laxative at doses approaching this level. Magnesium citrate at 25 mg is absorbed efficiently and is GI-inert at this dose. Note: this provides ~6% of RDA — it is a supplemental inclusion, not primary magnesium replacement.

Provides tartness and drives the mixed-solution pH to 3.5–4.2, which improves palatability significantly. At high sodium concentrations, a small acid dose masks the salty-bitter character of the electrolyte mix and adds a refreshing citrus edge. Without citric acid, high-sodium electrolyte mixes taste noticeably medicinal — palatability becomes a compliance issue in long events where athletes must continue drinking despite flavour fatigue. The acid contribution to beverage pH is relevant for athlete comfort but does not meaningfully acidify the blood or gut in normal use.