What kind of carbohydrate? continue...

Protein

The amount of protein needed by athletes is a controversial subject which has been debated for many years. Traditionally, weightlifters and athletes in other 'power' sports have believed that consuming vast quantities of protein will enhance muscle development. On the other hand, scientists have generally maintained that the protein needs of all athletes can be met by the same recommended daily allowances (RDA) as those for sedentary individuals.

Many research studies over the past decade have not resolved the controversy. However, as a very small amount of protein is used for energy during endurance sports, certain researchers now believe that the RDA of 0,8 grams per kilogram body mass per day might be insufficient for those who are involved in endurance-type exercise. Some (but not all) studies also seem to indicate that exercise which needs a good deal of strength (such as weight-lifting) may increase protein requirements. At the same time, there is no evidence that excessive amounts of protein (such as the 2-2,5 grams per kilogram body mass, per day commonly consumed by power trainers) will have any added benefit.

How much protein does an athlete in fact require? While there are no definite recommendations, studies have suggested this may be between 1 and 1,5 grams per kilogram body mass per day or 12 to 15%of the total energy intake. But before you reach for that protein _supplement, it must be emphasised that protein deficiencies among athletes are extremely rare. For example, a diet consisting of 14 300 kilojoules (3 400 calories), 14 % of which is derived from protein, provides about 119 grams of protein. An athlete who weighs 80 kg will therefore consume about 1,5^-grams of protein per kilogram per day. This diet is thus quite capable of supplying the increased protein requirements of strenuous physical activity.

Vitamins

Vitamins play an important role in regulating and assisting the breaking down of macronutrients for energy production and muscular contraction, as well as the formation of red blood cells. All of these functions are essential in exercise performance. Two questions are usually asked when looking at the vitamin-exercise connection:

• Does exercise affect vitamin requirements?
• Does vitamin supplementation improve exercise performance?

Vitamin requirements depend on the energy source of the working muscle. Exercise has been shown to increase the need for vitamin C and riboflavin (vitamin B2). However, it has also been proved that supplementation fails to increase the ability of athletes to train. Low thiamine (vitamin B1) intakes show no measurable effect on performance. Vitamin deficiencies in sportsmen and women are very uncommon and any increased demand for vitamins is usually met simply by the increased overall energy intake of the athlete. Studies of the effects of vitamin supplementation on performance have consistently found that there is no improvement in performance in athletes who have a balanced diet with an adequate vitamin intake. However, special care must be taken by those athletes who consume less than 5 000 kJ (1 200 cal) per day to ensure that their diets contain enough in the way of vitamins. This low energy intake is more common among female endurance athletes and ballet dancers.

Minerals

Like vitamins, minerals play an essential role in various exercise- related functions. The most important macrominerals and trace elements in an athlete's diet are sodium, potassium, magnesium, calcium and iron.

Sodium and potassium, which are usually referred to as 'electrolytes', play a major role in the amount of fluid in the body. Trivial amounts of both are lost in sweat, but even those athletes who sweat excessively rarely need to supplement their diets with either salt (sodium chloride) or potassium. The average diet contains 3 to 4 times more salt than necessary and simply by eating sufficient fresh fruit and vegetables, our potassium requirements are easily met. Magnesium deficiency is rare in athletes, partly due to the fact that it occurs in many foods and partly because sweat losses are very small. Magnesium does play an important role in the formation of glycogen, the storage form of carbohydrate in muscles and the liver.

Iron plays a major role in relation to exercise. The lack of it is the most common nutritional deficiency in the world and the most important in relation to runners, especially female runners. Energy intakes of less than 5 000 kJ (1 200 cal) are not enough to supply the amount of iron which a female sportswoman needs. Iron supplementation may then be necessary.

Water

Water can also be referred to as a nutrient as it is so essential to life. One of its many functions in exercise is that of heat regulation. The amount of water needed during an exercise event depends mainly on the duration and intensity of the exercise and the body weight of the athlete. As a general guide, 500 ml per hour is thought to cover most athletes' requirements.

Does sugar make you fat?

Although obesity is not classified as a disease, it is associated with a variety of diseases and since it is a problem - or potential problem - for so many people, the role of sugar in its development and treatment needs to be looked at carefully.

Firstly, overweight, and later obesity, develop as a result of an imbalance between your energy intake (from food) and energy output (the energy used for daily living, including basic body functions and any exercise you do). When you take in more energy than you are using, the body stores the additional energy as body fat. The source of this extra energy is immaterial; it makes no difference where the additional kilojoules come from. In other words, it is not eating one particular food but rather eating too much overall that leads to weight gain. It is possible to put on weight by eating (or drinking) too much of anything.

In practice this would of course be extremely difficult in the case of bulky foods with a high moisture content - such as certain vegetables - simply because it would be difficult to eat enough of these foods to provide kilojoules in excess of your energy needs. By contrast, in the case of concentrated, energy-dense foods such as rich desserts, fried foods or chocolate, it is all too easy to eat enough to lead to an excessive energy intake. Sugar, being a carbohydrate, is not the worst offender in this respect - fat is a far more concentrated source of energy - and it has been said that sugar is often 'guilty by association' because many so-called 'fattening foods' are high in both fat and sugar. For example, in the case of chocolate, sugar contributes approximately 33°k of kilojoules, compared to the fat contribution of over 50%.

Studies have shown that fat people don't eat more sugar than lean people, neither do they have more of a sweet tooth. They do however tend to eat more fat. In the light of recent research this makes sense, since we now know that it is easier to become overweight by eating too much fat than by eating too much carbohydrate.

Fat vs sugar

There are several reasons why fat is a bigger culprit than sugar when it comes to the problem of overweight. To begin with, as mentioned above, fat is far more energy-dense than carbohydrate - a gram of fat provides 38 kilojoules, whereas a gram of carbohydrate provides only 17. Secondly, carbohydrate seems to have a so-called thermogenic' effect, that is, it pushes up the body's metabolic rate so that kilojoules are burnt up faster. Lastly, the process by which the body converts dietary fat into body fat is a very efficient one - only 3% of the kilojoules are lost along the way. By contrast, when the body converts dietary carbohydrate into body fat, 23% of the kilojoules are lost. In other words, when you eat carbohydrate, only 77% of the kilojoules from that food are available as energy for the body.

To prevent weight gain, therefore, the best diet to follow is one that is low in fat and high in carbohydrate. This does not mean a diet high in sugar - the recommended carbohydrates in this case are complex carbohydrates, or starches. You can, however, include a limited amount of simple carbohydrates or sugar in your diet without fear of becoming overweight, as long as the total energy value of the diet is in line with your energy needs. Remember, it is the balance between your energy intake and your energy output that counts, rather than the type of food you eat. People who burn up a lot of energy (through, say, regular exercise or even nervous tension) can therefore eat more of these foods without fear of gaining weight, than can those whose energy requirements are much lower.

Sugar and slimming

When it comes to weight reduction, however, sugar should be looked at more carefully. The basic principle of a slimming diet is to select foods that are high in nutritional value but low in energy, so that although your kilojoule intake is restricted, all your nutritional requirements are met. Sugar provides only energy, so it is the first thing that should be excluded from a slimming diet. Interestingly, though, there is a school of thought which suggests that from a psychological point of view, a small quantity of sugar may be included in a slimming diet to help prevent feelings of deprivation and resultant binges. This obviously depends on the individual - some people crave sweetness and provided they can limit their consumption of sweet foods to one 'treat' a day, it may not be necessary for them to eliminate sugar totally. Of course, if once you've opened a packet of sweets you can't stop until you've eaten the last one - or if you're one of the lucky ones who seldom craves `something sweet' - it would be simpler to cut out sugar completely!