Electrolytes Explained: Sodium, Potassium, and Magnesium for Active People

Electrolyte products are a billion-dollar market. Packets, tablets, powders, and drinks all promise to replace what you lose in sweat. For some people, they fill a genuine need. For others, they are expensive salt water.

Understanding what electrolytes actually do, how much you lose during exercise, and when plain water is perfectly adequate will save you money and help you make better decisions about your training nutrition.

What electrolytes are and what they do

Electrolytes are minerals that carry an electrical charge when dissolved in water. Your body uses them to conduct nerve impulses, contract muscles, regulate fluid balance, and maintain blood pH. The three most relevant to exercise and supplementation are sodium, potassium, and magnesium.

Sodium

Sodium is the primary electrolyte lost in sweat. It regulates fluid balance outside your cells, and it is essential for nerve signalling and muscle contraction. The adequate intake for sodium is 1,500 mg per day, with an upper limit of 2,300 mg for the general population. Most people eating a Western diet consume 3,400 mg or more daily without trying.

Sweat sodium concentration varies enormously between individuals: from 200 mg per litre of sweat to over 1,500 mg per litre. The average is roughly 900 mg per litre. A person exercising hard for 90 minutes in warm conditions might produce 1.5 to 2 litres of sweat, losing 1,350 to 1,800 mg of sodium. That is a significant amount, and it is not replaced by plain water.

Potassium

Potassium regulates fluid balance inside your cells (the counterpart to sodium's role outside cells). It is critical for heart rhythm and muscle function. The adequate intake is 2,600 mg for women and 3,400 mg for men. Most adults fall short: average intake in the US and UK is roughly 2,500 mg.

Sweat contains potassium at roughly 200 mg per litre, far less than sodium. Exercise-related potassium losses are modest. The bigger issue is chronic dietary shortfall rather than acute sweat losses. Bananas get all the credit (422 mg per banana), but potatoes (926 mg per medium potato), spinach, avocados, and beans are all richer sources.

Magnesium

Magnesium is involved in over 300 enzymatic reactions, including energy production, protein synthesis, and muscle and nerve function. The RDA is 400 to 420 mg for men and 310 to 320 mg for women. Surveys consistently show that 50% or more of adults in Western countries do not meet the RDA from diet alone.

Sweat magnesium losses are small (about 5 to 15 mg per litre), so exercise is not a major driver of acute depletion. The real issue for active people is that magnesium requirements may be higher during intense training due to increased metabolic demand, and dietary intake is often already insufficient.

How much do you actually lose in sweat?

Sweat rates and electrolyte concentrations vary by individual, fitness level, heat acclimatisation, genetics, and environmental conditions. That said, rough estimates are useful for planning.

• Light exercise (30 to 60 minutes, moderate intensity): 0.5 to 1 litre of sweat. Sodium loss: 250 to 900 mg. Potassium loss: 100 to 200 mg.
• Moderate exercise (60 to 90 minutes, higher intensity or warm conditions): 1 to 1.5 litres of sweat. Sodium loss: 900 to 1,350 mg. Potassium loss: 200 to 300 mg.
• Heavy exercise (90+ minutes, high intensity, heat): 1.5 to 3+ litres of sweat. Sodium loss: 1,350 to 2,700+ mg. Potassium loss: 300 to 600 mg.

If you notice white residue on your skin or clothes after exercise, you are likely a salty sweater (higher sodium concentration). These individuals benefit most from sodium replacement during and after prolonged exercise.

When you actually need electrolyte supplementation

Not every workout requires electrolyte replacement. Here is a practical framework.

Water is enough

For exercise lasting under 60 minutes at moderate intensity in temperate conditions, plain water is sufficient. Your body has enough stored electrolytes to handle the losses, and your next meal will replace what you used. This covers the majority of gym sessions, casual runs, and recreational sports.

Electrolytes become relevant

Consider electrolyte supplementation when:

• Exercise lasts longer than 60 to 90 minutes
• You are exercising in heat or high humidity
• You are a heavy or salty sweater
• You are doing two-a-day training sessions with limited recovery time
• You follow a low-carb or ketogenic diet (these increase sodium excretion)
• You experience muscle cramps, headaches, or unusual fatigue during or after exercise

Hyponatraemia (dangerously low blood sodium) is rare but serious. It occurs most often in endurance events lasting 4+ hours when athletes drink large volumes of plain water without replacing sodium. Marathon runners and ultra-endurance athletes should always include sodium in their hydration strategy.

DIY electrolyte mix vs commercial products

Most commercial electrolyte products charge a significant premium for ingredients that cost pennies. Here is what a basic homemade electrolyte drink contains and what it costs.

Simple DIY recipe (per 1 litre)

• 1/4 teaspoon table salt (about 600 mg sodium)
• 1/4 teaspoon salt substitute (potassium chloride, about 350 mg potassium)
• 2 tablespoons honey or maple syrup (optional, for palatability and carbohydrate)
• Juice of half a lemon or lime (flavour plus a small amount of potassium)
• 1 litre of water

Cost per serving: roughly 5 to 10 pence. A comparable commercial product costs 50 pence to 2 pounds per serving. The electrolyte content is similar.

When commercial products earn their price

Commercial mixes offer convenience, precise dosing, and better flavour. Some include additional ingredients like magnesium, B vitamins, or specific carbohydrate ratios designed for endurance performance. If you train seriously and value convenience, they are reasonable. If you are looking to save money and do not mind measuring, DIY works just as well for the core electrolytes.

Electrolytes on a low-carb or ketogenic diet

Low-carb diets increase electrolyte needs for a specific physiological reason. When carbohydrate intake drops, insulin levels fall. Lower insulin causes the kidneys to excrete more sodium, which in turn drives potassium and magnesium losses. This is why the first week or two of a ketogenic diet often includes headaches, fatigue, and cramping, commonly called 'keto flu.'

The fix is straightforward: increase sodium intake to 3,000 to 5,000 mg per day (through salting food liberally and optionally using broth or electrolyte drinks), get potassium intake up to 3,000 to 4,000 mg through diet or supplements, and supplement magnesium at 200 to 400 mg daily. Most keto-adapted athletes report that adequate electrolyte intake resolves the symptoms entirely.

Signs you might need more electrolytes

Electrolyte imbalance shows up as practical symptoms before it shows up on lab tests:

• Muscle cramps during or after exercise: often attributed to magnesium or potassium, but sodium depletion is the most common exercise-related cause.
• Headache after long workouts: frequently a sodium issue, especially in warm conditions.
• Unusual fatigue or brain fog during training: can indicate overall electrolyte depletion, particularly on low-carb diets.
• Dark urine despite drinking water: may indicate that you are drinking water but not retaining it because sodium is too low to maintain fluid balance.
• Heart palpitations or irregular heartbeat: potassium and magnesium are both critical for cardiac rhythm. Persistent palpitations warrant medical evaluation, not just supplementation.

Dosing guidelines for active people

These ranges cover most recreational and serious athletes. Endurance athletes with very high sweat rates may need the upper end or beyond.

• Sodium: 1,000 to 2,000 mg during exercise lasting 90+ minutes. Spread across the session, not all at once. Post-exercise: salt your food generously.
• Potassium: 200 to 400 mg during exercise (most products provide this). Focus on dietary sources for your baseline: potatoes, bananas, spinach, beans, avocados.
• Magnesium: 200 to 400 mg daily from a supplement (glycinate or citrate are well-absorbed forms). This addresses the chronic dietary shortfall rather than acute exercise losses.

Common mistakes

• Drinking too much plain water during long events: dilutes blood sodium and increases hyponatraemia risk. Match fluid intake to thirst, not to a fixed schedule.
• Using electrolyte products for 30-minute gym sessions: unnecessary for most people. Water is fine.
• Ignoring dietary potassium: most electrolyte products are heavy on sodium and light on potassium. Diet remains the primary potassium source for nearly everyone.
• Fearing salt: for active people who sweat regularly, the general public health advice to limit sodium does not apply in the same way. If you exercise intensely and sweat heavily, you need to replace what you lose.

How Stack Almanac helps

Stack Almanac tracks electrolyte supplements alongside the rest of your stack, flags interactions (magnesium and certain medications, for instance), and shows your total daily mineral intake in one view. If you are combining an electrolyte powder with a standalone magnesium supplement and a multivitamin, the app totals your magnesium from all sources and alerts you if you are approaching the upper limit.