Nutritional needs for competitive sports and active living

If you wish to train for competitive sport or simply to keep fit, you can do much to maximize the effort you put into your exercise routine by paying attention to your diet and avoiding the pitfalls if dehydration. Intense, strenuous exercise appears to increase the body's need for anti-oxidant minerals and vitamins. These nutrients will help to reduce soreness after exercise and minimize damage to tissues and joints that can be caused by free radicals.

Keeping the food balance right

When you undertake serious training or take regular prolonged exercise, around 50-60 per cent of your calorie intake should come from carbohydrate, at least half of which should be whole grains, pulses and starchy vegetables. Up to another 25 per cent of calories should come from good-quality protein, and between 15 and 30 per cent from fat. For a 3,000kcal diet this would mean 50-100g (2-3oz) of fat, much of which should come from vegetable sources, such as olives, avocados, seeds, nuts, and oily fish.

Maintaining your energy

The body stores carbohydrate as glycogen in the muscles and liver. These stores are increased by regular training and by a diet rich in carbohydrate. Glycogen provides energy by being broken down into glucose, and is also needed to release energy stored in the body's fat. As you use up these stores, your body temperature rises and you start to sweat. If the lost fluid is not replaced, your performance will deteriorate.

Sports drinks

• Minimize fluid loss by drinking before, during and after exercise, especially in warm weather

• Take a snack two hours before training and refuel your glycogen stores with a carbohydrate meal after training

• Increase your glycogen stores by gradually eating more carbohydrate during the week before a big event, but this should not be done more than four times a year

• Avoid sudden weight changes: if you need to gain or lose weight, take your time and only alter your weight by approximately 0.5-1kg (1-2Ib) a week

Loss of fluid through perspiration is best replaced by drinking water. Water containing small amounts of sugar and sodium is absorbed into the body more quickly, but too much salt and/ or sugar slows water absorption, and discomfort may occur.

You can make your own isotonic drinks by diluting one part of fruit juice with one part of water, or one part of fruit squash with four parts of water, and adding 1-1.5g of salt to each litre. Some commercial sports drinks contain glucose polymers, which may be helpful if you exercise vigorously for more than 90 minutes. Avoid caffeine as it increases your fluid loss (as urine) and can cause anxiety and/ or a rapid heart beat.

Sporting needs

Supplements containing 100-200 per cent of the daily recommended intake may be useful, especially mineral supplements as many of these are lost in sweat. However, excessive supplementation will not enhance performance further, and may lead to nutritional imbalance. SODIUM AND POTASSIUM are needed in correct balance to control the distribution of fluid within the cells of the body, in the tissues between the cells, and in the circulation. They enhance muscle action and prevent spasm, and are both lost in sweat.

CALCIUM AND MAGNESIUM help muscles to contract and relax efficiently, and are essential for strong bones. Magnesium is lost through the skin in sweat, so you need plenty of food rich in magnesium if you take regular exercise.

IRON is needed to replace the red blood cells that are lost by being physically damaged during exercise. It is especially important for women of childbearing age because iron deficiency leads to loss of energy and poor endurance.

CHROMIUM helps the body to regulate the level of sugar in the blood and is lost in the urine more quickly during exercise.

SILICON is needed for tissue flexibility. VITAMIN C keeps the connective tissue strong and may reduce the effects of injury. The B-VITAMINS are lost more rapidly during exercise. VITAMIN A, BETA-CAROTENE, VITAMIN E AND SELENIUM help to reduce tissue damage during exercise and to maintain performance.

To avoid dietary imbalance, mineral and vitamin supplements should not usually be taken in large doses except with professional guidance.