Electrolytes & Sodium: The Complete Guide

Longevity culture focuses on molecules and devices, but dehydration and sodium depletion quietly wreck training consistency — and consistency is the longevity variable that compounds.

Sodium maintains plasma volume. Potassium and magnesium support cardiac rhythm and muscle relaxation. You cannot run a high VO₂ max program or sauna protocol on plain water if you are dumping salt in sweat.

Exercise-associated hyponatremia (low blood sodium) is documented in endurance sport when athletes over-drink plain water. The opposite problem — inadequate replacement during heavy sweat losses — is more common in gym and sauna biohackers who fear salt.

Low-carb diets increase renal sodium excretion in the first weeks. Fasting and GLP-1-induced appetite suppression reduce food sodium intake without reducing sweat losses. Heat, altitude, and long Zone 2 sessions amplify the gap.

Magnesium is a separate but synergistic topic — see the magnesium guide. Electrolyte packets often pair sodium with potassium; magnesium is frequently taken separately at night.

Baseline eaters: if your diet includes restaurant food, deli meat, and snacks, you may need zero supplemental sodium on rest days. Start by noticing symptoms, not megadosing.

Active / low-carb / fasting: 1 electrolyte serving (typically 500–1000mg sodium) before or after training, sauna, or a long fasted walk. LMNT and similar mixes use sodium chloride, potassium, and magnesium without sugar.

Heavy sweat days: pre-load with water + electrolytes 30–60 minutes before session; replace roughly what you lose — weigh yourself before/after hot runs for a rough guide.

Night stack: magnesium glycinate/threonate separate from high-sodium packets if GI upset occurs.

Same-day: fewer headaches and less post-sauna dizziness when you were under-replaced. Zone 2 may feel smoother — heart rate drift sometimes drops when volume is restored.

Weeks: if nothing changes, you probably did not need more sodium. Reassess diet first.

Hypertension, kidney disease, heart failure, and certain medications require medical guidance — not Reddit sodium targets.

Over-replacement without sweat losses can raise blood pressure in salt-sensitive people.

Cost: LMNT-style boxes run roughly $1–2 per stick; DIY salt + potassium + magnesium is cheaper but less convenient.

Huberman and Attia both normalized 'salt your water' for athletes. r/keto and r/fasting repeat the same lesson. Skeptics note most Americans already over-consume sodium via food — the target audience is exercisers and low-carb adapters, not everyone.