Training regimes by our top athletes are becoming increasingly scientific – and paid dividends with a huge medal haul in Beijing. Nutrition plays its part, as DR CLIVE HUNT, Senior Lecturer in Nutrition, at the University of Huddersfield explains
We are recommended to increase physical activity to at least five to seven half-hour sessions of moderate intensity exercise per week
EVEN as our victorious Team GB athletes returned from the Olympics to the acclaim of a proud nation thoughts were already turning to London 2012, with hopes of an even better medal tally.
This will require considerable resources in terms of facilities for training, coaching, medical and other support.
As performance boundaries are pushed further and further, more and more scientifically-based support is necessary, and this includes appropriate nutrition.
So what are the most important aspects to consider?
First of all, calories. The commonly quoted daily calorie requirements are 2,500 and 2,000 kcals for an average man and woman respectively. But this assumes a relatively sedentary lifestyle. For optimum health we are recommended to increase physical activity to at least five to seven half-hour sessions of moderate intensity exercise per week, which would increase our calorie requirement by about 100 to 200 kcals per day.
However, considerably more may be needed by athletes in intense training, commonly giving requirements of 3,000 to 4,000 kcals per day and sometimes even more. So what sort of foods should this come from?
Proportions of calories recommended from macronutrients are fairly similar to non-athletes, except a bit more from carbohydrate (55-60% of calorie intake), a bit less from fat (25-30%) and about the same for protein (10-15%).
Regarding carbohydrate, some sugar is OK but excessive amounts cause tooth decay, hence starchy carbs. such as bread, pasta, rice and potatoes are recommended. This helps to maintain stores of glycogen in the muscles and liver, which is drawn on as the major fuel source during physical activity.
As glycogen becomes depleted, fat and protein are used more and more by the body to produce energy but these are less efficient than carb, in that there is a lower energy yield per litre of oxygen consumed.
Endurance athletes should stock up with carbs before and after the event, and sometimes even during (eg glucose drinks during marathons or long-distance cycling).
Another issue is protein. Requirement for non-athletes is quoted as 0.8g of good quality protein per kg body weight per day, which works out at about 55g per day for the average man and 45g for a woman.
But do athletes in intense training require more? This remains a controversial issue, particularly given evidence that training increases efficiency of protein utilisation. However, in sports nutrition circles, requirement is commonly quoted as somewhat more – approx. 1.0 to 1.6g/kg/day for both strength and endurance athletes. This is to allow for extra muscle growth and repair, but also because there may be extra oxidation of protein to provide energy in endurance events.
Good quality protein is found in foods such as meat, fish, eggs and cheese, but also from appropriate mixtures of vegetable proteins such as cereals and pulses eaten together.
Loss of water through sweat and from the lungs is another important consideration in intense activity, as dehydration will rapidly impair performance.
There may also be substantial loss of the electrolytes, sodium and chloride, in sweat – hence their inclusion in some sports drinks (though not in too high a concentration as this would cause dehydration!).
Generally, mineral and vitamin requirements are not increased, or only slightly, over normal recommendations.
Any increases in calorie or nutrient requirements that there are, are usually easily covered by the increased appetite and food intake accompanying increased physical activity. However, there may be some performers who deliberately restrict food intake for weight control (eg gymnasts, dancers, boxers). Over time, this could deplete nutritional status and impair performance. Under these circumstances, nutrient supplements may be necessary, although the best advice would be to ensure adequate food intake.