Understanding Electrolytes So You Can Hydrate Better

What’s the secret to replenishing your fluid losses after every training session?


Words Jackie Green
Photos Pixabay.com and Pexels.com

What are Electrolytes?

Electrolytes are minerals that hold an electric charge and are crucially involved with hydration, nerve signalling, maintaining blood pressure and muscle function including that of the heart.

While most of us eat more than enough salt (sodium chloride) in our daily diet, we are also likely to be eating insufficient amounts of other minerals necessary for a truly well-balanced function. Magnesium is a key mineral that our bodies often do not have enough of.

Here’s a chart showing four essential minerals that our bodies need, and the foods that they can be found in:

Mineral Food Sources
Potassium All fruit and vegetables are rich in potassium especially tomatoes, peppers, potatoes, avocado, oranges, beetroot, squash, courgette (zucchini) and green leafy veg like spinach and kale, coconut water
Sodium Celery, beetroot, bok choy, peppers
Magnesium Nuts and seeds, especially almonds, cashews, sunflower and sesame seeds, oats, avocado and dark green leafy greens
Calcium Milk, yoghurt and cheese, calcium enriched soya milk, dark green leafy veg, okra, tofu, prawns, pulses (legumes) such as chickpeas, cannellini and black beans

Let’s look at Sweat

Does sweat drip off your nose or run down your legs on a run? Do your clothes thud onto the floor? Sweat rates are individual, varying from 300-2400ml per hour and are highly dependent upon:

  • Duration of exercise
  • Intensity
  • Fitness (well-trained people actually tend to start sweating sooner )
  • Heat acclimatisation
  • Humidity
  • Gender (women tend to sweat less than men)
  • Age (children sweat less than adults)

In addition to losing water, some people are ‘salty sweaters’, losing large amounts of sodium through their skin. Tell-tale signs are white patches on drying sweaty clothes and sweat stinging your eyes.

Sweat contains a substantial amount of sodium and a small amount of potassium, calcium and magnesium, varying slightly in content across different individuals. Just tasting sweat we can tell that it’s salty.

  • The average amount of sodium in sweat is 1g per litre
  • ½ teaspoon (2.5g) salt contains 1g of sodium

Many products boast added electrolytes, including magnesium and potassium, however, sodium is the primary electrolyte lost in sweat and the one that needs replacing to aid re-hydration. Magnesium, potassium and calcium need to be taken daily from food but not particularly after sweating.

Fluid and Electrolyte Guidelines

Before Exercise Drink 5-10ml per kg body weight 2-4 hours pre-run.

Sodium pre long run may help fluid retention. Salt on food or an isotonic drink would both do the job.
Fluid during Exercise   400-800ml fluid per hour.

Water for exercise up to 1 hour, isotonic sports drink and water for longer durations.  
Electrolytes during exercise Unnecessary for most recreational runners

Have a sodium and potassium containing isotonic sports drink for fluid replacement and to help maintain muscle contraction if any of the following apply:

- Sweat losses greater than 1.2l/hour
- Exercise exceeds 2 hours
- Tendency to cramp

Athletes competing in endurance events, especially in a hot and humid climate, consider having salty foods e.g. crackers, marmite/ vegemite sandwiches and high sodium sports drinks or adding extra salt or electrolyte replacements to a standard isotonic sports drink.  
After Exercise The volumes of sweat losses are unknown for most people. Drink according to your thirst and continue drinking little and often over the next 2-4 hours.

If sweat volume is known, drink 125-150% of  that volume over the next 5 hours.

Drinks containing carbohydrate are better retained than water alone. However, water alone is perfect for most people after runs lasting less than 60 minutes.

Add a little salt to food in the  2-4hours post exercise

Eat a couple of portions of fruit and some veg to obtain a broad range of electrolytes and additional fluid too.

If you’re feeling cheap or want to try something on your own, you can easily make your own isotonic drink at home. Here’s all you need:

Homemade Isotonic Drink (5% carb, 1g sodium)

  • 500ml fruit juice
  • 500ml water
  • ½ tsp (2.5g) salt

The Takeaway Message

  • Commit to eating at least two portions of fruit and five portions of vegetable daily to maintain magnesium and potassium status
  • Calcium is crucial for muscle contraction. Have three portions of dairy foods daily or non-dairy equivalents
  • Stay hydrated
  • Sodium is the primary electrolyte in sweat and can easily be replaced by adding a little salt to food after exercise
  • Electrolyte replacements are unnecessary for most but can useful for endurance athletes
  • You can save money and make a homemade isotonic drink!
About the Writer:

Jackie Green is a British nutritionist and dieititian, registered with the Health Professions Council in the UK and a is member of The British Dietetic Association, The Singapore Nutrition and Dietetic Association and Sports Dietitians Australia. Jackie worked as an oncology dietitian at The Royal Marsden Hospital in UK for many years, during which time she helped adults and children overcome the eating difficulties which often arise from cancer or as a side effect of treatment.


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