Nutrition: Think “Drink!”

What, when and how much do you need to drink?

Keep the fluids flowing

Virtually everyone recognises that energy drinks can be more effective than water in endurance sport, but you also need to know how much to drink and when, and with the plethora of drinks on the market, which drink is best for you.

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Know your drink

The two central factors causing exercise fatigue are dehydration and carbohydrate depletion, so the range of energy drinks available can be summed up as a trade-off between energy replenishment and rehydration. However, once carbohydrate levels in drinks are raised beyond a certain level they inhibit fluid absorption.

Knowing your isotonic from your hypotonic and hypertonic is therefore crucial.

Hypotonic drinks have a low-level of carbohydrate (typically 2-4 percent) and are aimed primarily at rehydration. UK examples include Lucozade Hydroactive or Powerade Aqua. Hypertonic drinks have high levels of carbohydrate (up to about 17 percent) but are poor rehydrators. The original Lucozade Energy is an example, as is Red Bull (though Red Bull is a slightly different type of drink which will be explored later).

Isotonic drinks include products like Lucozade Sport, Powerade and Gatorade. These contain about 5-7 percent carbohydrate and aim for a balance of carbohydrate replenishment and rehydration. There are also recovery-specific drinks which throw protein into the mix. Clearly then, choosing the right drink depends on your priorities and when you drink it.

Know how much

A new study by the Gatorade Sports Science Institute assisted by MontrealUniversitylooked at the effect of ingesting different amounts of carbohydrate during a 120-minute cycle, followed by a 20km time trial.

They found that even small levels of carbohydrate improved time trial performance but that the optimum was somewhere between 30 and 60g per hour, probably closer to the latter for most people. That’s between half a litre and a full litre of isotonic drink per hour. 

Any more or less is likely to be sub-optimal, according to lead researcher John Eric Smith. “At lower levels of carbohydrate intake, performance is still improved but the demand for use of body stores of carbohydrate is greater,” he says. “Excessive carbohydrate intake can cause distress and stomach upset due to the slowed absorption of fluid.”

The trick for each individual is to find where they are within the half-litre to full litre per hour range. Many factors influence this, including sweat rate, electrolyte losses and exercise duration. 

The key is to drink at a rate that reduces dehydration without resulting in unnecessary weight gain that’ll slow you down or putting yourself at risk of hyponatraemia, a rare but potentially fatal condition caused by drinking so much water that your sodium levels drop to dangerously low concentrations. 

According to Smith, ‘salty sweaters’ are most likely to be at the top end of the range. “Salty sweaters typically have a dry residue appearing on their clothes and hats,” he says. “This may indicate the need for intake that is greater than normal.”

Know what to drink when

During endurance activity, isotonic drinks are probably best because these combat dehydration and carbohydrate depletion simultaneously. But when should you start taking fluids on? 

Researchers from MaastrichtUniversity examined this using 10 male subjects on a three-hour cycle. They found sports drinks reduced the amount of glycogen used all through the exercise, not just at the end when the going got tough.

“Athletes should initiate sports drink consumption immediately at the onset of exercise to maximize its effect on glycogen sparing,” the researchers concluded. So drink little and often and don’t wait till you’re thirsty!

But what about before and after the race? After exercise, protein becomes as important as carbohydrate and rehydration to avoid muscle soreness and damage, so a carbohydrate-protein mix drink will be your best bet.

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Prior to the race, provided you’ve eaten well, your carbohydrate stores should be topped up so there may be little gain from an isotonic or hypertonic drink. Unless it’s very hot, a hypotonic drink may also be of little benefit. In fact, before competition it may be better to pick drinks for mental, rather than physical, effects.