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.

What kind of carbohydrate?

Athletes often don't know what form of carbohydrate they should be consuming. Does it make a difference if you eat carbohydrate mostly in the form of sugar or should you eat only complex carbohydrates (such as bread, pasta, rice, cereals and potatoes)? Some people regard sugar as 'deadly', while others wouldn't do without it and consider it a necessary part of their diets. Nutritionists advise that sugar and sugary foods should be limited to between 5 and 10 % of total daily energy intake. In other words, a moderate amount of sugar and sugary foods is not considered harmful. The higher the energy content of your diet, the larger the quantity of sugar you can eat. However, sugar and foods containing a large amount of sugar should never take the place of unrefined complex carbohydrates such as wholewheat bread, whole grain cereals and sweetcorn, as these supply other vital nutrients which sugar does not.

Sugar is a useful addition to the diets of athletes who need large amounts of energy, as it supplies a 'calorie-dense' food source. Athletes who take part in triathlons, for example, may find that they simply do not have the time when training two to three times a day to eat the amount of food they need to perform well. By including a small amount of calorie-dense foods - such as those rich in sugar - in their diets, these triathletes are able to fulfill their energy requirements without spending all their free time eating! However, those athletes who try to maintain very low body weights and who consequently eat very little, should obviously keep sugar and foods high in sugar to a minimum.

The fibre factor

Fibre, though not classed as a nutrient, and not actually absorbed by the body, is an important component of our diets, whether we are athletes or sedentary individuals. Found exclusively in plant foods, a low intake of fibre has been linked to various 'Western' diseases. Much of the natural fibre in plant foods is lost in food refinement and this together with a high consumption of animal foods, results in the average Westernized diet being low in fibre. We should all aim to eat at least 30 grams of fibre per day.

Fat

Fat is the other nutrient that is a chief source of energy in our diets. Athletes and the public in general should aim to consume no more than 30% of their total daily energy in the form of fat. Endurance athletes who consume between 60 to 70 % of their energy in the form of carbohydrates, may have to limit their fat intake to 20-25 % of their total calories to allow for those calories obtained from carbohydrates and protein. The main advantage of fat is that it is a very concentrated source of energy (9 calories/37,8 kilojoules per gram). When fat is used as a source of fuel during exercise, it has the advantage of 'sparing' glycogen. A diet high in saturated fat and cholesterol can cause raised blood cholesterol levels, even in athletes who train vigorously, so both should play a limited role in any diet.

Secrets of Athletes and weight control

For many sportsmen and -women, there are distinct advantages to maintaining an optimum ratio between body fat and lean body mass. Gymnasts, wrestlers, ballet-dancers and even jockeys strive for a low mass and a high strength-to-mass ratio. Fat tissue does not contribute to the generation of force or power and therefore, must be carried as 'dead' weight in activity involving strength or during any weight- bearing exercise (for example, in a sport like distance running). In fact, leanness is often a good predictor of performance. However, for many athletes, the 'quest for thinness' may become a pre-occupation.

An athlete may try to control body weight in one of several ways. Firstly, he or she may attempt to reduce and maintain a minimal body mass. This is commonly achieved in what amounts to chronic 'undernutrition'- which may in fact result in nutritional deficiencies. It has been shown that it is difficult to take in adequate amounts of certain vitamins and micronutrients - such as B12, folic acid, iron and calcium - when food energy intake is below 5 000 kilojoules (or 1 200 calories) per day.

In addition, chronic low energy (kilojoule) intake in endurance trained athletes will result in certain changes in metabolism, in order to 'spare' energy. An athlete with a low intake may be able to eat less to maintain his or her current body mass, than one with a normal intake. There may be changes in thyroid hormone function, menstrual irregularities in women and a decrease in 'resting metabolism' (see page 128). All these factors point to undernutrition.

Many athletes - particularly young ones - aim to increase their lean body mass or 'muscle bulk', so as to improve performance in some sport. This may involve special diets, protein supplements, drugs to stimulate appetite and anabolic drugs (such as the much-publicised anabolic steroids). A recent study of 76 local resistance-trained athletes revealed that they were taking in nearly 3 times the RDA (recommended dietary allowance) for protein, and then supplementing their diet with protein powders. These sportsmen would be expensive to feed - and, as already shown, their efforts would be to no avail.

It is important for an athlete to recognize that attempts at weight gain in order to increase muscle mass are only effective if accompanied by a resistance training programme which overloads the muscle. In addition, there is no strong scientific argument for supplementing the diet with protein to this extreme, and the long-term consequences on kidney function are as yet, unknown. Drugs, especially anabolic steroids, also have potentially harmful long-term side effects; in addition, they are illegal and generally considered as a 'cheating' method of improving performance.

Finally, many sports involve specific weight categories and certain athletes are regularly involved in 'making weight' prior to competition. Examples of these sporting activities include body building, boxing, martial arts, horse racing and collegiate wrestling. There has been a great deal of research into the weight control practices and dietary patterns of American collegiate wrestlers. In a study of over 700 high school wrestlers, it was estimated that these athletes lost between 2 and 12% of their body mass within 2-48 hours prior to competition. This 'weight cycling' was repeated between 5 and 30 times per season for each wrestler! Sixty-nine college wrestlers were surveyed and results revealed that the average weight a wrestler needed to lose to compete in a specific category was approximately 4,5 kg, 3 days prior to competition. All of those surveyed gained weight in the off-season, and tended to flucuate between 5 and 9 kg above competition weight each week during the season!

The rapid weight losses achieved by these athletes usually involve cutting down severely on food and fluid intake and 'thermal' methods designed to lose water through sweating (plastic suits, saunas, etc.). But studies show that this can be counterproductive, since a loss of as little as 2% of total body weight through dehydration causes reduced exercise and heat tolerance, which in turn may result in poor performance.

There is also evidence that athletes who regularly undergo 'weight cycling' or 'yo-yo' dieting and weight loss may experience long-term changes in growth and metabolism. Wrestlers who constantly have to 'cut weight' in order to compete have been shown to have a slower metabolic rate than those who can compete without losing mass. So, while leanness may be a good indicator of performance in some sports, the 'quest for thinness' itself may have a detrimental effect. Manipulating body weight through weight 'cycling' may also result in long-term changes in metabolism; the athlete should rather strive for a balance in weight control which will improve his or her performance in the long-term.

It is unlikely that manipulating food intake or a single isolated nutrient will lead to enhanced performance on its own. An overwhelming number of studies have shown that supplementing a balanced diet, containing sufficient protein, vitamins and minerals has no benefit on athletic performance. A consistent and well planned training programme is still the most effective way of improving athletic performance. However, good nutrition supports the training programme in ensuring optimal performance, and sound nutritional practices will allow the athlete to achieve his or her potential.