Sports drinks have three basic ingredients — water, sugar and salt.
When you exercise you lose water as sweat, as much as two litres an hour from strenuous exercise in hot weather. If you sweat more than 2% of your body weight your heart is placed under stress, your body temperature goes up, and your physical and mental performance declines.
But forget about drinking ‘eight glasses of water a day’ — that’s an urban myth. Six glasses (1.5 L) of almost any fluid should be ample. Exactly how much water we actually need depends on how much we get with our food and how much we lose as sweat.
Ads for sports drinks are eloquent on the subject of “hydration”. Certainly the sugar and salt these drinks contain are at the right concentrations to maximise the speed with which water moves from your gut into your bloodstream. But plain water is absorbed almost as quickly and is perfectly adequate for moderate exercise or if you’re exercising for less than about an hour.
A recent study found no real differences overall between the hydration ability of plain water and three brands of sports drink. And there’s little evidence that any one sports drink is better than any other on the market.
But the sense of thirst is slow to react to dehydration, so if you’re exercising hard in hot conditions it’s a good idea to drink before you become thirsty. In fact you need to drink before, during and after exercise.
The sugars in sports drinks are also supposed to replenish the fuel you use during exercise. The body stores fuel as carbohydrates in the muscles and the liver and releases sugar into the blood stream for instant energy. But after prolonged exercise the carbohydrate stores are depleted and blood-sugar levels can drop.
Studies have shown that supplying a steady source of sugar during exercise fights off fatigue and enhances performance, but it has to be strenuous exercise for an extended period. It takes about an hour of intense exercise — like a fast run or hard cycling — before the body depletes its reserves enough to benefit from extra carbohydrates. With lower intensity exercise, such as jogging, it may take two hours or more.
There’s evidence that sports drinks can improve performance, but only if you’re an elite athlete. If you’re simply an active person who jogs, swims or goes to the gym a couple of times a week, you don’t need sports drinks.
And if you’re concerned about putting on weight, it’s unlikely that you actually need that extra energy. Our bodies have evolved to store any excess energy as fat. If you’re an elite athlete, you’ll be training for several hours a day, using up plenty of energy, and the extra kilojoules from a bottle or two of a sports drink make little difference to your energy balance.
But it’s a different story if you’re just playing a bit of tennis and going for the odd lunchtime jog. One bottle of some of the popular brands of sports drink hits you with 9-10 teaspoons of sugar.
In the table we’ve compared how many minutes of jogging are fuelled by 600 mL of each brand of sports drink for a boy of 12 years, a woman weighing 60 kg and a man weighing 70 kg. (Not all of the sports drinks come in 600 mL bottles but this is the most common bottle size and you’d need to drink at least this much fluid if exercising for about an hour under hot conditions.)
Most brands give you enough fuel for well over 20 minutes jogging. If you’re not exercising for that long, that’s sugar (and kilojoules) you don’t need.
Sports drinks contain ‘electrolytes’ — mostly sodium chloride (ordinary salt) and potassium chloride. Replenishing the body’s electrolytes is less important than the ads would have you believe.
It’s true that sodium, which helps regulate the body’s fluid balance and plays a role in muscle contraction, is lost in sweat; to a lesser degree, so is potassium, which is also involved in muscle contraction. But most of us already get too much salt in our regular diet (see Healthy eating) so your usual food intake should be more than enough to replace any electrolyte losses.
A 600 mL bottle of some sports drinks (including top-selling Gatorade) gives you more than 10% of the maximum recommended daily intake of sodium.