Sport nutrition for young athletes

MACRONUTRIENTS

Macronutrients, such as carbohydrates, protein and fats, provide the fuel for physical activity and sports participation for young athletes

MICRONUTRIENTS

Although there are many vitamins and minerals required for good health, particular attention should be devoted to ensuring that athletes consume proper amounts of calcium, vitamin D and iron. Calcium is important for bone health, normal enzyme activity and muscle contraction. The daily recommended intake of calcium is 1000 mg/day for four- to eight-year-olds and 1300 mg/day for nine- to 18-year-olds (7,8). Calcium is contained in a variety of foods and beverages, including milk, yogurt, cheese, broccoli, spinach and fortified grain products.

Vitamin D is necessary for bone health and is involved in the absorption and regulation of calcium. Current recommendations suggest 600 IU/day for four- to 18-year-olds (8). Normal values of vitamin D also vary depending on geographical location and race. Athletes living in northern latitudes or who train indoors (eg, figure skaters, gymnasts, dancers) are more likely to be vitamin D deficient (2). Sources of vitamin D include fortified foods, such as milk, and sun exposure. Dairy products other than milk, such as yogurt, do not contain vitamin D.

Iron is important for oxygen delivery to body tissues. During adolescence, more iron is required to support growth as well as increases in blood volume and lean muscle mass (1). Boys and girls nine to 13 years of age should ingest 8 mg/day to avoid depletion of iron stores and iron-deficiency anemia (7). Adolescents 14 to 18 years of age require more iron, up to 11 mg/day for males and 15 mg/day for females (7). Iron depletion is common in athletes because of diets poor in meat, fish and poultry, or increased iron losses in urine, feces, sweat or menstrual blood (2). Therefore, athletes, particularly female athletes, vegetarians and distance runners should be screened periodically for iron status (2). Iron-rich foods include eggs, leafy green vegetables, fortified whole grains and lean meat.

FLUIDS

Fluids, particularly water, are important nutrients for athletes. Athletic performance can be affected by what, how much and when an athlete drinks. Fluids help to regulate body temperature and replace sweat losses during exercise (8,9). Environmental temperature and humidity can affect how much an athlete sweats and how much fluid intake is required (1,9,10). Hotter temperatures and higher humidity make a person sweat more, and more fluid is needed to maintain hydration. Dehydration can decrease performance and put athletes at risk for heat exhaustion or heat stroke (1,9,10).

Proper hydration requires fluid intake before, during and after exercise or activity. The amount of fluid required depends on many factors, including age and body size (9,10) (Table 2). Before activity, athletes should consume 400 mL to 600 mL of cold water 2 h to 3 h before their event (1,2,10). During sporting activities, athletes should consume 150 mL to 300 mL of fluid every 15 min to 20 min (1,2,10). For events lasting less than 1 h, water is sufficient (4). For events lasting longer than 60 min, and/or taking place in hot, humid weather, sports drinks containing 6% carbohydrates and 20 mEq/L to 30 mEq/L of sodium chloride are recommended to replace energy stores and fluid/electrolyte losses (3,4,5,9). Following activity, athletes should drink enough fluid to replace sweat losses (Table 2). This usually requires consuming approximately 1.5 L of fluid/kg of body weight lost (1,10). The consumption of sodium-containing fluids and snacks after exercise helps with rehydration by stimulating thirst and fluid retention (1,2,10). For non-athletes, routine ingestion of carbohydrate-containing sports drinks can result in consumption of excessive calories, increasing the risks of overweight and obesity, as well as dental caries and, therefore, should be avoided (4).