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Electrolytes: what they do, and what to check on the label

CORE PROTOCOL TEAM5 MIN READ

Network diagram linking sodium, potassium, calcium and magnesium nodes around a central hub, beside the headline Electrolytes

Electrolyte powders and tablets are some of the most common products in sports nutrition, and the front of the tub rarely tells you the one thing that matters. Here is what electrolytes are, how much athletes really lose, when food and water are enough, and what to check before you buy.

What electrolytes are

Electrolytes are minerals that carry an electrical charge in the fluids of your body: sodium, potassium, magnesium, calcium and chloride. They help move water around the body and let nerves and muscles do their job. You lose them in sweat, and sodium is the main one in sweat and the one most worth planning around.

How much sodium do you actually lose?

Far less predictably than most labels suggest. A review of data from 506 athletes found that the average whole-body sweat contained about 36 mmol of sodium per litre, which is roughly 830 mg. Individuals ranged from about 420 mg to about 1,630 mg per litre. Average sweat rates were around 1.2 litres an hour, but ran from under 0.3 to nearly 6.

Put those together and two people doing the same session can lose very different amounts. Someone sweating half a litre an hour at the low end of salt concentration loses around 200 mg of sodium an hour. Someone sweating two litres an hour at a higher concentration can lose ten times that. A single "one scoop fits all" dose cannot be right for both of them.

When food and water are enough

For most people most of the time, they are. The NHS advises adults to have no more than 6 g of salt a day, and most of the salt in a typical UK diet already comes from everyday packaged foods such as bread, cereals and ready meals. A short, easy session in mild weather does not need an electrolyte drink on top.

Electrolytes earn their place when the maths changes:

  • sessions or events that run well beyond an hour
  • heat or humidity
  • heavy sweating, for example white salt marks on your kit afterwards
  • two sessions close together, with little time to eat and drink between them
  • competition, where you cannot afford to get it wrong

What the label should tell you

  • Sodium in milligrams per serving. The word "electrolytes" on the front means nothing by itself. A product can list five minerals and contain very little sodium.
  • Salt or sodium? Salt (sodium chloride) is about 40% sodium by weight, so 1 g of salt holds roughly 400 mg of sodium. Make sure you are comparing the same thing.
  • How much water, and how many servings. Work out the sodium per litre of drink and per hour of exercise, not just per scoop.
  • Carbohydrate and caffeine. Some mixes are partly an energy drink. That can be useful mid-session, but count it with everything else you take.
  • Overlap. Many products also carry magnesium, potassium or zinc. If those turn up in your other supplements as well, the totals add up faster than the labels suggest.
  • Amounts. A blend that lists ingredients but not quantities cannot be judged.

Do they stop cramps?

This is the most common reason people buy them, and the evidence is weaker than the marketing. The idea that cramps come from losing electrolytes rests mostly on anecdotes and case series, and prospective studies have not backed it up. Current research points more towards muscle fatigue. That does not make electrolytes pointless, because they still replace sodium lost in sweat. It means they should not be sold, or bought, as a cramp cure.

More is not better

Drinking far more than you need carries its own risk. The 2015 consensus statement on exercise-associated hyponatraemia, which is dangerously low blood sodium, advises letting thirst guide how much you drink rather than following a fixed schedule. Extra sodium is not harmless either, particularly if you have high blood pressure or kidney problems.

That is why electrolytes are best treated as a scaled tool rather than an all-day habit. In the protocols Core Protocol builds, sodium is sized to the length and heat of the event, in a range of 300 to 700 mg an hour, and it is a during-session product rather than something taken all day.

Find your own number

You do not need a lab to get a rough idea. Weigh yourself before and after a typical session, then add whatever you drank. The difference in kilograms is roughly your sweat loss in litres. Do it a couple of times in different conditions and you will know whether you are a light sweater or a heavy one, which tells you far more than the tub does.

Where this leaves you

Electrolytes are not a trend to follow or avoid. They are one input, and the right amount depends on how long you train, how hot it is and how much you sweat. A protocol treats them that way: sodium scaled to the session, counted alongside the magnesium and potassium in everything else you take, and reviewed when your training changes. We covered why in why static stacks fail serious athletes.

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