Readers often ask me which sports beverages they should drink when exercising.
Consequently, I was interested to hear what speakers had to say at a symposium on "What is the Ideal Sports Beverage?" held in Midrand last week.
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Hydration
An ideal sports beverage should hydrate the body when the athlete is exercising and losing fluid via sweat.
Prof Tim Noakes of the UCT/MRC Research Unit for Exercise Science and Sports Medicine spoke on "The importance of hydration in athletes – what is known today?" He pointed out that humans have become the lords of creation because they have adapted to hunting in the heat (all other predators take a nap during the day when it's hot!), and are able to cool off by sweating.
In addition, humans have adapted to being moderately dehydrated without suffering harm.
Therefore, although athletes who exercise strenuously in the heat, do need to replace water, they should not go overboard and drink so much that they develop a condition called dipsomania.
Excessive and unnecessary intake of liquids, even when exercising to the limit, can disrupt the electrolyte balance of the body (the concentrations of sodium and potassium in body fluids), and can be dangerous. In some cases, athletes who ingested too much water became so depleted of sodium that they died.
Prof Noakes cautioned that an athlete's thirst is the best indicator of how much water he or she should drink during exercise. "Drink to the dictates of your thirst" is the golden rule.
Don't drink if you're not thirsty and avoid doing excessive, vigorous exercise when it's very hot. If you have to train despite the weather, make a plan to exercise when it's cooler (at night or in the early morning) and drink just enough water to quench your thirst.
Carbohydrates
Dr Andrew Bosch, who is also at the UCT/MRC Research Unit for Exercise Science and Sports Medicine, discussed 'How much and which carbohydrates should be in the ideal sports beverage'.
Ever since 1924, we've known that sports drinks need to contain some carbohydrates to fuel performance. In a classic experiment, a dog called Joe ran for four hours on water alone, but managed to run for 16 hours when glucose was added to his water!
A physiological body function called "gastric emptying" determines how rapidly the carbohydrates in a sports beverage will become available to the body as a source of energy.
Interestingly, enough corn starch, glucose polymers, glucose and fructose are absorbed from the stomach at the same rate. Research has shown that adding carbohydrate to sports beverages will delay fatigue and prevent exhaustion in athletes.
According to Bosch, a sports beverage that contains 7-10% glucose polymer (7-10g of glucose polymer per 100ml) generally agrees well with athletes and sustains their performance.
He also emphasises that athletes should drink about 400ml of such a sports beverage before exercising. Thereafter, they should ingest 100ml every 15 minutes during exercise, as dictated by thirst.
Proteins
Until recently, most sports beverages used during competitions did not contain anything other than water, carbohydrates, sodium and potassium.
However, some researchers are now suggesting that the addition of protein to sports beverages that are used before, during and after competition may improve athletic performance. Two speakers addressed this subject at the symposium: Dr Amanda Claassen and Dr Stephan Siebrecht, who hails from Germany.
Dr Amanda Claassen, from the Virgin Life Centre, spoke on the role of protein in sports beverages. She pointed out that there is a continuous buildup and breakdown of proteins in muscle tissue during physical activity.
If a sportsman or -woman ingests amino acids (the building blocks of proteins) from foods or supplements, this decreases protein breakdown and improves protein synthesis in the muscles (i.e. improved repair of damaged muscles).
In the post-exercise phase, there is generally an increase in protein synthesis in muscles. Ingesting protein at the rate of up to 2g per kg body weight per day can support muscle tissue repair.
Dr Claassen said that higher protein intakes would not improve the situation and could put strain on the kidneys. A 70kg athlete would, therefore, not need more than 140g of protein per day to ensure good muscle recovery.
It's interesting to note that females are more efficient when it comes to tissue protein repair, so that female athletes usually required 10-15% less protein than their male counterparts to achieve the same protein production. So, a 70kg female athlete would only need 70g - 7g (10%) = 63g of protein to achieve the same level of muscle repair as the 70kg male athlete.
There is some evidence that the so-called branch chain amino acids may help to protect muscle tissue against damage. It should also always be kept in mind that carbohydrates have a protein-sparing effect and that, for efficient recovery of muscle tissue damage caused by intensive exercise, sportsmen and -women need to replace lost carbohydrates as well as lost protein.
Dr Claassen warned against the use of single amino acids such as arginine, carnitine or aspartic acid, as research in this field indicates that single amino acid supplements can have a toxic effect. It is thus better to use whole protein or protein hydrolysates to supply the body with amino acids than to use single amino acid supplements.
Text copyright: Dr I.V. van Heerden, DietDoc
26 February 2007
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