As summer temperatures rise to record levels in Hong Kong, working out becomes a bigger challenge than ever. The more we sweat, the more important it is to keep well hydrated. But there is a lot of conflicting advice and confusion when it comes to what, when and how often to drink. Here, we bust some common hydration myths: Myth: by the time you feel thirsty, you’re already dehydrated Truth: feeling thirsty is the body’s way of telling us to drink. If you listen to your body, you’ll know when to drink and exactly how much to drink so you’re optimally hydrated, says Dr John Heiss, director of sports and fitness at global nutrition company Herbalife. Heiss, who has been developing sports nutrition products since his days as a PHD biochemistry student at the University of California, Los Angeles, was recently in Hong Kong to launch his latest creation, Herbalife’s CR7 Drive sports drink, which was created in collaboration with football superstar Cristiano Ronaldo. “Our bodies evolved over millions of years to accurately let us know when we’re thirsty,” says Heiss, a former competitive downhill skier, cross country runner, and cyclist. “If you drink according to the body’s thirst indicators, you’ll be in pretty good shape.” Myth: you’re not hydrated unless your urine is clear Truth: clear pee is actually a sign of overhydration, says Heiss, and this can lead to serious complications. If you are hydrated, your pee should be straw-coloured to transparent-yellow colour. Drinking too much can cause dangerously low blood sodium levels, a condition known as hyponatremia or water intoxication. Sustained, excessive intake of water, sports drinks, or other fluids – exceeding the body’s ability to eliminate fluids in the form of sweat and urine – is the major risk factor for exercise-associated hyponatremia (EAH). Symptoms typically include headache, vomiting, confusion and seizures, resulting from swelling of the brain (cerebral edema). Without immediate treatment, severe hyponatremia can be fatal. According to a consensus statement on EAH in the June 2015 issue of the Clinical Journal of Sport Medicine , the best approach to preventing potentially serious reductions in blood sodium level is to drink when thirsty. “Using the innate thirst mechanism to guide fluid consumption is a strategy that should limit drinking in excess and developing hyponatremia (low blood sodium) while providing sufficient fluid to prevent excessive dehydration,” according to the report’s lead author Tamara Hew-Butler of Oakland University. Myth: there’s a prescribed amount of water one must drink during exercise Truth: there is no one-size-fits-all prescription when it comes to hydration. Many years ago, it was advised that everyone needs to drink 1.2 litres per hour of exercise – but that didn’t take into account body size, weather conditions and exercise intensity, Heiss says. “Generally, people should start with 600ml per hour and then adjust to one’s needs.” You can lose up to three per cent of your bodyweight without any loss in performance, Heiss says. He says some studies have found that faster finishers at marathons tend to be more dehydrated than slower finishers. “People who are faster generally are not stopping and drinking as often. They might lose fluid but they get lighter and become more efficient at running,” says Heiss. One study in the British Journal of Sports Medicine looked at 643 runners at the 2009 Mont Saint-Michel Marathon in France. The runners were weighed before and after the race, and it was found those completing the race under three hours averaged 3.1 per cent weight loss, compared to 2.5 per cent for those who finished between three and four hours, and 1.8 per cent for those who took longer than four hours. Myth: a sports drink is necessary for hydration during exercise. Truth: someone working out very casually for an hour can simply have water, Heiss says. But if you’re doing pretty intense exercise or working out for longer than an hour, he suggests a sports drink that contains a mixture of minerals (in particular sodium) and carbohydrates. According to guidelines from the American College of Sports Medicine (ACSM), during exercise lasting fewer than 60 minutes, “there is little evidence of physiological or physical performance differences between drinking a carbohydrate-electrolyte drink and plain water”. For longer workouts, a carbohydrate consumption rate of between 30 and 60 grams per hour has shown to maintain blood glucose levels and sustain exercise performance. The ACSM recommends a drink with a carbohydrate concentration of not more than 8 per cent, as highly concentrated carbohydrated beverages slow the digestive system and could cause gastric distress. Myth: sports drinks are healthy Truth: if you exercise at a high intensity and/or for sustained durations, sports drinks can help boost performance. But if you don’t do sports, you don’t need a sports drink. “A sports drink and soft drink contain similar amounts of sugar, so if you’re drinking either without doing any exercise, it’s probably inappropriate,” Heiss says. Studies have also shown a link between consumption of sports drinks and irreversible damage to the teeth – the high acidity levels in the drinks erode tooth enamel, the glossy outer layer of the tooth. So, drink with purpose and in moderation. Myth: coconut water is an excellent natural sports drink Truth: in recent years coconut water has shot to fame as a natural sports drink, but studies show it’s not all that perfect. A 2012 study presented at the national meeting of the American Chemical Society found that coconut water contained up to 1,500 milligrams per litre of potassium, compared with up to 300 mg/litre for Powerade and Gatorade. Coconut water, however, had 400 mg/litre of sodium compared to 600 for the other two drinks. It had comparable quantities of magnesium and carbohydrates as the other drinks. Coconut water’s lower sodium content is where it fails as a good sports drink for people who engage in strenuous exercise that produces a lot of sweating, says researcher Chhandashri Bhattacharya of Northern Virginia Community College. Sweating makes people lose more sodium than potassium, and coconut water alone can’t replace that lost sodium. Heiss adds: “Coconut water tends to take water out of the blood and into your cells, so you have cellular swelling and a constriction of blood volume – it’s almost like the opposite of hydrating. If you’re working out for an hour at the gym, drinking coconut water is going to be fine. But if you’re running a marathon, having high levels of potassium can create a problem.” Myth: all sports drinks are the same. Truth: there are subtle differences between different brands. When choosing a drink, Heiss recommends going with flavour first. Then find something that your stomach digests easily. Consider what type of sugar the sports drink contains; glucose is more easily digested than other sugars (many sports drinks are just pure sucrose, which is tougher to digest and leaves you feeling bloated). Some minerals, such as sodium citrate and potassium citrate dissolve more easily and are used by the body more easily. Look for a drink that has between 250mg and 600mg of sodium, 300mg of potassium and 25 grams of carbs per 500ml serving, Heiss suggests. Avoid any artificial flavours, sweeteners, colours and chemicals.