Peta Bee investigates whether those drinks we load up on pre- and post-workout are really what our bodies need

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If there is a mantra to which we have all subscribed at the gym in recent years, it is to prehydrate and rehydrate, to drink before we are thirsty and, at all costs, to avoid becoming parched. For to do so would be a death knell to our workout efforts, we are told, and place us at serious risk of the most feared of all fitness states: dehydration. Water won’t suffice. What we’ve come to rely on is the flood of flavoured, carbohydrate-containing drinks, awash with minerals and electrolytes that sell themselves as essential to performance and health. Sports drinks are undeniably ubiquitous, but do we really need them?

Experts are convinced not, at least unless we are planning an impending endurance feat of marathon proportions. While sports drinks are positioned as being essential for replacing the fluid and body salts lost in sweat at the same time as boosting flagging glycogen stores with the tiny particles of carbohydrate they contain, there is little to support the notion for the average exerciser. “You need to be exercising quite hard for an hour or more to make sports drinks worthwhile,” says John Brewer, professor of Applied Sports Science at St Mary’s University, Twickenham. “Otherwise you are effectively giving yourself an unnecessary dose of calories in the form of sugar.”

In 2014 the Australian authors of a paper in the Journal of Medical Ethics expressed “ethical concerns” about the marketing of sports drinks as fitness and health-enhancing for which, they claimed, “there is no strong scientific evidence”. A promotional campaign by Lucozade Sport was banned by the Advertising Standards Agency last year for stating it hydrated you “better than water”.

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And a recent paper by Canadian exercise scientists at Brock University suggests that sports drinks don’t help workout performance at all. Admittedly, the study was small, involving 11 trained cyclists who wore IV drips as they pedaled on indoor bikes. Some of the cyclists were given a saline solution similar to a sports drink while the others were give mock drops that weren’t especially rehydrating.

Neither group knew which type they had been given. At the end of the trial, researchers found no difference in performance. Even when they were dehydrated at up to 3 per cent of their body weight, “no impairment was seen in exercise in the heat”, said lead researcher Stephen Cheung. It’s the latest in a long line of damning evidence that the benefits of sports drinks are overplayed. Here’s what you need to know:

Check your balance

You don’t need to pre-hydrate like a camel by stocking up on extra fluids and carbs before the average workout. “It’s a real misconception that you need to fuel for exercise in this way,” says Dr Sarah Schenker, a nutritionist who has advised many top footballers. “Drinking enough water and eating ordinary food will suffice for most people.” Checking the quality and quantity of your urine can help to tell if you are adequately replacing fluid losses. Dark and scanty generally suggests it is concentrated with metabolic waste and you need to drink more, although your urine may be darker if you take vitamin supplements (especially vitamin C), so volume is often considered a better indicator.

They could harm your teeth

Being both sugary and highly acidic, sipping sports drinks is notoriously bad for your teeth. Several studies have shown that they gradually erode tooth enamel, the glossy outer layer of teeth. Damage to tooth enamel is irreversible and without the protection of enamel, teeth become overly sensitive and are more likely to decay and develop cavities. Some researchers claim they are as bad for your teeth as cola and sweetened fizzy drinks . If you must have them, drink through a straw to minimise contact with teeth.

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Watch your weight

Linia Patel, a sports dietitian with the British Dietetic Association, says too many people believe that the more sugar-laden sports drinks they consume, the fitter they can become. “Sports drinks are highly sugary solutions,” she says. “With about 140 calories a bottle, they will offset much of the calorie gains you have made in a workout and will inevitably lead to weight gain if you take too many.”

You can overdrink

In recent years sports scientists have discovered that it is just as risky to drink too much during exercise as it is to consume too little fluid. Indeed, in many endurance events like the London Marathon, hyponatraemia - or fluid intoxication - is more prevalent than dehydration. Caused by sodium levels and other body salts (or electrolytes) becoming dangerously dilute, hyponatraemia can result in dizziness, vomiting, respiratory problems and fatigue. "During intense or prolonged exercise, the kidneys are unable to excrete fluid as efficiently as normal," says John Brewer, Professor of Applied Sports science at St Mary’s University in Twickenham. "In extreme cases, water is retained, especially in highly absorbent brain cells, and the pressure causes the body to shut down its primary functions.”

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Rely on thirst

Such is the concern that people are consuming too many fluids prior to and during exercise, scientists have produced new recommendations in the latest issue of the Clinical Journal of Sport Medicine, urging people to rely on thirst as an accurate indicator for how much they need to drink. Drink when you need to during exercise and it “should limit drinking in excess and developing hyponatremia (low blood sodium) while providing sufficient fluid to prevent excessive dehydration” is the straightforward advice.