Sports drinks

There is a growing range of drinks which can be used before, during and after exercise (including some other drinks marketed as ‘sports drinks’ with questionable nutritional credentials).

Reasons for drinking sports drinks

The main reasons for drinking sports drinks (as opposed to plain water) are:

  • sports drinks are an effective way to replenish your body’s energy levels by providing easily digestible carbohydrates;
  • they may replace essential minerals (e.g. sodium, potassium, magnesium, chloride) which you lose when you sweat;
  • dilute sugar solutions are absorbed by the body more quickly than plain water, so sports drinks can (depending on the concentration – see below) accelerate fluid replacement;
  • drinks containing sodium increase the urge to drink and the palatability of the drink, thereby encouraging you to drink more.

Sports drinks are especially useful for endurance runners during long training runs and races (any run longer than an hour); and for shorter distance runners who want to replenish their energy stores after a tough workout.

Types of sports drinks

The concentration of a sports drink determines the effect it has on you, and the extent to which it speeds up water absorption.  Broadly speaking, a drink with between 3g and 8g of carbohydrate per 100ml accelerates fluid absorption compared to plain water.

Sports drinks are of three kinds:

  • isotonic – the same concentration as normal bodily fluids and so easily absorbed;  commercial isotonic drinks typically contain 4g – 8g of carbohydrate per 100ml.  Isotonic drinks balance the need for rehydration and refuelling;
  • hypertonic – more concentrated than normal bodily fluids; usually containing more than 8g of carbohydrate per 100ml; because of their concentration they are absorbed more slowly than isotonic drinks;
  • hypotonic – less concentrated than normal bodily fluids; typically less than 4g of carbohydrate per 100ml.  Absorbed faster than plain water, but containing less carbohydrate than isotonic drinks.

If the weather is hot, you should give more priority to fluid replacement, and choose a hypotonic or isotonic drink; in cooler conditions, you may find a hypertonic drink beneficial.

The optimum carbohydrates for sports drinks are glucose, maltose, glucose polymers (also known as maltodextrins) and soluble, branch-chained starches with a high glycaemic index (see Chapter 6).  Fructose, the sugar found in fruits, is not so well absorbed by the body during exercise, and can lead to an irritable stomach, but is fine in small quantities.

Glucose polymers are especially useful because they are molecules of carbohydrate in a form which does not add as much to the concentration of the drink as pure glucose. Because they are less sweet than simple sugars, they don’t make a high-carbohydrate drink taste so sickly.

What to look for in an ideal sports drink
by Tim Noakes

1. Palatability
The most scientifically formulated drink is of no value if it is so unpalatable that it cannot be drunk.

2. Carbohydrate concentration of 5 to 10 per cent
Higher carbohydrate concentrations only become important near the end of prolonged, competitive exercise when the desire to drink falls, but the need for carbohydrate replacement is greatest.

3. Carbohydrates from a variety of sources
A mixture of carbohydrate sources (glucose, fructose, maltodextrins) is necessary (i) to maximise palatability and (ii) to maintain a low-to-moderate osmolality [ie absorption rate] of the drink

4. Sodium concentration of 20 to 60 mmol.l-1
The higher sodium concentrations aid fluid balance when athletes are able to ingest fluid at high rates

5. All the rest is marketing.

Tim Noakes, ‘The Lore of Running’, 2001.

Try to avoid drinks which contain sweeteners such as aspartame or saccharine, since these taste sweet but are not digested (which is why they are low calorie). These may confuse the blood sugar regulation system.

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