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TRAINING

Nutritional concerns for the young cyclist

Compiled by Jacques Rossouw


February 2005

Endurance sports like running, cycling, swimming, and cross-country skiing are distinguished from other sports by the duration of the training and competition. In addition, the intensity of effort is sustained at a fairly constant submaximal intensity. The prolonged nature of these sports requires attention to intakes of adequate fuel and fluids. With regard to micronutrients, research has shown that iron and calcium status or intakes of the young cyclist may require special consideration.

Fluids
The duration and intensity of endurance training, especially when it occurs in a hot, humid environment, can predispose the endurance athlete to significant fluid and electrolyte loss2. Similar to adults, when children or adolescents are provided only water to drink they do not replace their losses as well as they do with a flavored drink or a flavored carbohydrate-electrolyte solution3. The presence of sodium in a beverage not only enhances the drive to drink but also helps to replace some of the sodium lost in sweat. It is also interesting to note that older adolescents tend to sweat more than younger adolescents4.

Energy
Research suggests that children require more energy per kilogram of body weight during physical activity than do adults4. Many studies that have used dietary records have found that young athletes, in particular female athletes, have low energy intakes1. Inadequate energy intake in combination with high energy expenditures can create a negative energy balance that can produce a delay in the onset of puberty, short stature, low bone mineral density, increased risk of injury and slower recovery, menstrual irregularities, dehydration, and nutrient deficiencies1.

Macronutrients
Little research has been conducted on the protein or carbohydrate needs of the child and adolescent athlete. Consistent with studies on adult athletes, the needs of both macronutrients are likely greater due to exercise. It is recommended that the adult endurance athlete generally consume carbohydrate in an amount of 5 to 10 g/kg/d to ensure adequate replenishment of glycogen levels and protein in an amount of 1.2 to 1.7 g/kg/d to maintain lean body mass. As the intensity of the physical activity increases, so does the body's reliance on carbohydrate as fuel. Stored carbohydrate is a special consideration for the endurance cyclist because it is available in such limited supply. During sustained exercise at fairly high intensity, over time the endogenous carbohydrate supplies are depleted and will force the cyclist to reduce the level of intensity, if the exercise is to be sustained. When glycogen stores are depleted, the cyclist can obtain as much as 5% to 10% of energy needs from oxidation of body protein during exercise. Because this is an undesirable response in growing young cyclists, the recommendation of adequate carbohydrate intake to maintain adequate muscle and liver glycogen concentrations is further justified1.

Any time you eat carbohydrate, your blood glucose (sugar) rises. In turn, your pancreas releases insulin, a hormone, which facilitates the entry of glucose into the muscle cells where it is used to produce energy. During, or just prior to competition, you don't want a high insulin level to drive down your blood glucose when you need to feel energetic. Foods that have a low to moderate Glycemic Index (GI) don't cause a dramatic release of insulin. Conversely, foods with a high GI will send insulin rushing into your blood stream1. Thus, it is recommended that the young cyclist consume food or drinks with a low to moderate GI prior to and during competition. High-GI foods and drinks should only be consumed after competition or training, and during carbo-loading, to facilitate the rapid replenishment of muscle and liver glycogen stores.

TABLE 1: GLYCEMIC INDEX (GI) OF FOODS AND DRINKS COMMONLY CONSUMED BY CYCLISTS
 LOW GI (<55)Consume 3 hrs before cycling  MODERATE GI (55-70)Consume mainly during cycling  HIGH GI (>70)Consume mainly after cycling
Fructose
Wholewheat Pronutro* with skim milk
Cooled mealiemeal porridge
Nature's Source low-GI muesli's*
All Bran* (Kellogg's) with skim milk
Sustagen meal-in-a-glass
Ensure (vanilla) meal-in-a-glass
Mageu Number One*
Spaghetti, no sauce
Tastic Rice
Sweet potato
Flavored yoghurt*
Milk*
Mixed grain bread*
Sugar free jam
Milk chocolate*
OrangesOrange juice (Liquifruit)
Apples
Apple juice (Liquifruit)
Vitrace* energy drink
(MRF)
CarboFuel (USN)
 Honey
Sucrose (table sugar)
Bananas
Sultanas
Banana bread
Oats, cooked (Woolworths)
Samp and beans*
Boiled potato
Pizza, cheese*
Bar One*
Zone Bar (PVM)
Condensed milk*
Cordial & cold drinks (Coke)
Corn syrup
Grape juice
Vooma (USN)
Cytopower (USN)
GlucoseDextrose
Maltodextrin
Marie biscuits
Super C sweets
Jelly beans
Cookies
Cakes
White & brown bread
Snackbread
Rice cakes
Corn Flakes
Rice Crispies
Cocopops
Oat-so Easy
Weetbix (Bokomo)
Samp
Mashed potato
Baked potato
French fries
Sports drinks with sugar(e.g. Energade, Lucozade, Powerade, Game)
CarboFuel (USN)
Sources: Steenkamp & Delport (2002)5, Burke (1998)6 & Clark (2003)7

The DRI (dietary reference intakes) recommends a range of 0.73 to 0.85 g of protein per kilogram of body weight for sedentary boys and girls ages 9 to 18 years. It is not yet known how these requirements increase in children due to endurance training. Based on research conducted on endurance and strength in adult athletes, many sports nutritionists and exercise physiologists recommend protein intakes for these groups that exceed the DRI (1.2 to 1.6 g/kg/d and 1.2 to 1.7 g/kg/d, respectively). Provided the cyclist is consuming adequate energy from a variety of foods, consumption of adequate protein generally is not an issue.

Selected micronutrients
Puberty in general increases the need for iron due to increases in hemoglobin mass, tissue deposition, growth spurt, and onset of menstruation in females. Iron depletion and deficiency have been observed in endurance athletes1. Iron status depends on a balance of intake and absorption versus loss. Regular, intense, endurance exercise may predispose the athlete to greater iron losses. Dietary surveys of athletes often report iron intakes to be inadequate.

Although exercise itself does not increase the body's need for dietary calcium per se, the body of an exercise- or diet-induced amenorrheic female athlete may require more. This type of athlete may be at greater risk of decreased bone mineral density and increased stress fractures. Therefore, greater calcium intakes, such as 1500 mg/d, may be necessary. These athletes may undergo not only significant energy expenditures but also diminished energy intakes. This may be due to a number of factors, including participation in a sport such as long-distance running, which attracts individuals who are more likely to be obsessed with control of body weight.

The intense training of some endurance cyclists has been found to decrease concentrations of estrogen and testosterone. Of particular concern is the decline in estrogen in some female cyclists, which can lead to decreases in bone mineral density. When decreased estrogen is coupled with low intakes of total energy, protein, and calcium, the cyclists may be placed at serious risk for stress fractures and possibly premature osteoporosis (the female cyclist need to do additional weight-bearing exercises like running to strengthen the bones and thus delay the onset of osteoporosis).

References
1. Petrie, H. J., Stover, E.A. & Horswill, C. A. 2004. Nutritional concerns for the child and adolescent competitor. Nutrition 20 (7-8): 620-631.
2. Bar-Or, O. & Wilk, B. 1996. Water and electrolyte replenishment in the exercising child. Int J Sport Nutr 6: 93.
3. Wilk, B. & Bar-Or, O. 1996. Effect of drink flavor and NaCl on voluntary drinking and hydration in boys exercising in the heat. J Appl Physiol 80: 1112.
4. Bar-Or, O. 2001. Nutritional considerations for the child athlete. Can J Appl Physiol 26: 186.
5. Steenkamp, G. & Delport, L. 2002. The South African Glycemic Index Guide. GIFSA.
6. Burke, L. 1998. The Complete South African Guide to Sports Nutrition. Oxford University Press: Cape Town.
7. Clark, N. 2003. Nancy Clark's Sports Nutrition Guide Book. Third ed. Human Kinetics: USA.



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