Proper Intake of Macronutrients & Micronutrients – Young Athletes

Posted by admin July 12th, 2009

Critical Micronutrients:
Current research and trends point to deficiencies in calcium, iron, folate, vitamin B6, and zinc for young athletes. The functions, risks of deficiency, and recommendations for each vital micronutrient follow.

Proper intake of calcium is needed to support bone growth, increase bone mass, and aid in nerve impulses and muscle contraction. Poor calcium intake can lead to decreased bone mass and consequential increased risk for stress fractures and other bone-related injuries. Because a young athlete’s growing bones cannot handle as much stress as an adult’s mature bones, optimum bone health is critical; overuse and overtraining injuries are more apt to occur in a pediatric or adolescent athlete. To ensure proper bone health, keep in mind that the adequate intake of calcium for children aged 9 to 18 is 1,300 milligrams per day.

While iron is noted for its oxygen-carrying capacity, it is also a major player in the energy metabolism of carbohydrate, protein, and fats. For this reason, young athletes with iron-deficiency anemia may experience performance inhibition ranging from decreased work capacity to extreme fatigue, impaired immune function, and impaired cognitive reasoning. Because iron deficiency is one of the most common nutrient deficiencies in the world, it is imperative that professionals working with young athletes are aware of the athlete’s iron intake. On the other hand, it is important to note that iron toxicity is the most common cause of poisoning death in young children. If you want to avoid recommending a supplement, you can recommend food items that are high in iron, such as red meat and enriched cereals and grains, coupled with fruits and vegetables that are high in vitamin C, which aids in iron absorption.

B Vitamins
Both vitamin B6 (pyridoxine) and folate are members of the B-complex of vitamins and are critical components of energy metabolism and blood health. Both are critical for amino acid metabolism and good sources of each are enriched grain products and assorted animal products. Research differs on whether there are changes in folate and vitamin B6 levels during periods of heavy training. However, the conclusion is usually that exercise does not increase the requirements for these nutrients and the dietary reference intake should be followed. In general, a B-complex deficiency can lead to fatigue, muscle soreness, apathy, and loss of cognitive function.

While an extreme zinc deficiency is uncommon in the United States, athletes are at risk due to poor consumption of foods rich in this mineral. Zinc plays a role in more than 300 enzymatic reactions in the body and is critical for wound healing, tissue growth and maintenance, and immune function. Various studies have shown that zinc status directly affects basal metabolic rate, thyroid hormone levels, and protein utilization; thus, zinc is critical to athletes. Dietary protein enhances zinc absorption, and athletes who are most at risk of a deficiency may be vegetarians or those who primarily eat a grain-based diet. With the myriad critical functions to which zinc is linked, consumption of adequate levels of zinc should be stressed.

Critical Macronutrients:
With an increase in energy expenditure comes a subsequent need for an increase in the intake of carbohydrate, protein, and fat. Current research and trends point to deficiencies in overall total energy and carbohydrate intake. Also of concern is deficient fluid intake and consequent altered hydration status of young athletes. The functions, risks of deficiency, and recommendations for each vital macronutrient follows.

In athletes, poor carbohydrate intake results in inadequate glycogen stores and premature fatigue, which not only compromises performance but also forces the body to rely on another source for fuel: protein. Glucose from carbohydrate sources is essential to most body functions during exercise. If glucose is not available for use as fuel during physical activity, the body will take from its protein stores for energy via gluconeogenesis. Because carbohydrate is the preferred fuel for athletic performance, approximately 55% of total daily calories should come from carbohydrate. The young athlete has the capacity to store carbohydrate in the form of glycogen, but this capacity is limited, so carbohydrate must be consumed daily. Carbohydrate needs are based on body weight and intensity of activity. The American Dietetic Association (ADA) has set the following recommendations for the young athlete:
• 3 to 5 grams of carbohydrate per kilogram for very light intensity training;
• 5 to 8 grams of carbohydrate per kilogram for moderate or heavy training;
• 8 to 9 grams of carbohydrate per kilogram for preevent loading (24 to 48 hours prior); and
• 1.7 grams of carbohydrate per kilogram for postevent refueling (within two to three hours).

Protein is an essential part of the young athlete’s diet, and the role of protein for youth includes building, maintaining, and repairing muscle and other body tissues. It should be noted that an adequate protein intake with inadequate caloric intake prohibits protein balance, even when the recommended daily allowance for protein is consumed. Therefore, it is critical that young athletes consume enough calories to maintain body weight. While adult endurance and strength athletes may need more protein per pound of body weight, additional protein needs for young athletes have not been specifically evaluated. However, the ADA has set the following recommendations:
• Athletes who have just begun a training program require 1 to 1.5 grams per kilogram per day of protein.
• Athletes participating in endurance sports require 1.2 to 1.4 grams per kilogram per day of protein.
• Athletes who restrict calories must be certain to consume adequate protein for muscle building and repair. A minimum of 1.4 grams per kilogram per day is recommended.
• Vegetarian and vegan athletes should be counseled to ensure that adequate intake of protein is consumed from plant sources.
• Consuming an overabundance of protein can lead to dehydration, weight gain, and increased calcium loss. This is critical to monitor as research shows that the population of young athletes is already at risk for calcium deficiency.

While carbohydrate is often spotlighted as the preferred fuel for sports, there are some bodies of research suggesting that lipid or fat may be the preferred fuel for children. This may be due to the higher rate of fat oxidation in children. As a major energy source, fat is essential for light- to moderate-intensity exercise and for endurance exercise. Below are some easy-to-follow guidelines for consumption of fats:
• While a low-fat diet can be followed, it is important that young athletes consume an average of 20% to 30% of calories from fat.
• Like adults, young athletes should aim to significantly lower the amount of saturated and trans fat in their diet. The focus should be on an intake of healthy fat from plant oils and soft margarines made with vegetable oils and on limiting the amounts of fried and processed foods.

Maintaining fluid balance is critical for the young athlete. As rates of youth participation in endurance events climb, legitimate concerns about fluid status have arisen. Aside from the risk of heat-related illness, dehydration is strongly associated with fatigue during exercise. This risk is increased in certain environmental conditions such as high heat and humidity. Compared with adults, young athletes may be at a higher risk for altered fluid status for several reasons: Children experience greater heat stress and heat accumulation, and they have a greater ratio of surface area to body mass and absorb heat more readily. Signs of dehydration in children include dark urine, small urine volume, muscle cramps, reduced sweating, increased heart rate, headaches, and nausea. Specific recommendations for fluid consumption are as follows:
• Child and adolescent athletes should aim to replenish lost hydration stores during and after an event. This can be done by weighing the athlete before and after an event and replacing fluids lost (16 to 24 ounces for every pound lost).
• For activities lasting less than 60 minutes, select water for hydration.
• For activities lasting more than 60 minutes, select sports beverages for hydration, electrolytes, and energy from carbohydrate. Select a beverage that provides 6% to 8% carbohydrate.
• Lastly, be aware that children do not instinctively drink enough fluids to replace lost stores and thirst does not always indicate when the body is in need of more fluids.

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