P ART I Nutritional Concerns of Athletes
CHAPTER 3 CHAPTER 3 Nutritional Concerns of Child Athletes
A. Requirements
Nutritional assessment in children is based on maintaining growth within established parame- ters. Markers utilized for growth include Ht, BW, Wt/Ht, %BF, and BMI. Monitoring of these markers will reveal imbalance(s) of energy and/or nutrient intake over time. The World Health Organization,105 publishes nutritional recommendations intended to serve as guidelines for popu- lations of all nations.
1. RDA /DRI
Recommended Dietary Allowances106 (RDA) are the primary reference values utilized for evaluation and prescription of nutritional intake for healthy individuals in the U.S. The last edition
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was published in 1989.106 However, more recently, the Food and Nutrition Board (FNB) has begun to replace the RDAs with a new set of reference values for the U.S. and Canada known as Dietary Recommended Intakes107 (DRI). The DRIs include values for estimated average requirements, RDA, adequate intakes, and tolerable upper intake levels. The first publication includes values for calcium, phosphorus, magnesium, vitamin D, and fluoride. Use of the DRIs is encouraged, but information is limited to the nutrients listed above. Therefore, until publication of DRIs on all nutrients is available, the RDAs continue to be employed as the primary reference values.
2. Estimating Energy Needs
Recommended energy intake for age (Table 3.2) provides one method for estimating energy needs. Adjustments to match individual EE requirements should be accomplished based on mon- itoring of growth markers over time.108
Other modes that estimate energy needs include the REE method,108 doubly labeled water technique,109 direct and indirect calorimetry, and heart rate monitoring. The REE method calculates REE/kg of BW as a baseline of EE to which factors such as maintenance, activity, and growth (Table 3.3) are added. Although this method may be subject to wider individual variation, it is readily available and easily utilized in any setting. More-accurate methods, such as doubly labeled water technique, direct and indirect calorimetry, and heart rate monitoring are employed primarily for investigative purposes, and are not readily available outside the research setting.
3. Nutrients — Macro and Micro (Fuel Sources)
Intensity and duration of PA or exercise determines the source of energy (fuel) utilized by the body. CHO and fat serve as the major sources of energy (fuel) for muscle. PRO provides fuel during prolonged PA or training when CHO and fatty acids (FA) are limited in availability.110
PA requiring anaerobic or maximal effort over short periods of time such as sprints, gymnastics, football, figure skating, and ballet primarily utilize adenosine triphosphate (ATP) and phosphocre- atine (PCr) as fuel sources. Metabolism of CHO (glucose and glycogen) and FA provide these fuel sources. PA requiring intense effort over longer periods of time or endurance-type activities that involve aerobic mechanisms such as marathon running, basketball, soccer, ice hockey, and wrestling
Table 3.2 Recommended Energy and Protein Intakes for Age
Age REE Average Energy Needs Protein
(yr) (kcal/kg/d) (kcalAkg BW–1Ad–1) (kcal/d) (gAkg BW–1Ad–1)
Children 1–3 57 102 1300 1.2–1.8
4–6 48 90 1800 1.2–1.75
7–10 40 70 2000 1.0–1.5
Males 11–14 32 55 2500 1.0
Females 11–14 28 47 2200 1.0
Adapted from references 106 and 108.
Table 3.3 REE Method of Estimating Energy Needs
Factors x REE*/kg Body Weight Maintenance 0.2
Activity 0.1–0.25
Growth 0.5
Adapted from reference 108
*See Table 3.2 8199/C03/frame Page 49 Thursday, August 10, 2000 3:35 AM
50 NUTRITIONAL APPLICATIONS IN EXERCISE AND SPORT
initially utilize CHO as a fuel source. However, over time, FA and PRO provide energy-sustaining fuel sources.110
Energy and nutrient intake balanced with expenditure should provide adequate fuel for PA and exercise in children. Rankinen et al.111 investigated this hypothesis in athletic and non-athletic children. The authors assessed 43 female athletes(FA) (gymnasts, figure skaters, and runners), 49 male (MA) hockey players, 53 non-athletic female controls (FC), and 35 non-athletic male controls (MC). Mean ages of FA and FC were 11.4 ± 0.5 years and 11.5 ± 0.5 years, respectively. Mean ages of MA and MC were 12.5 ± 0.5 years and 12.4 ± 0.5 years, respectively. Four-day dietary intake and activity records, serum trace element status, and anthropometric measures were collected.
Analysis of dietary intake records indicated a significantly higher energy intake in MA than in MC, but not in FA and FC. However, when energy intake was calculated per kilogram BW, FA energy intake was significantly higher than FC. PRO intake was significantly increased in both MA and FA when compared with MC and FC. Dietary micronutrient intakes significantly increased in MA when compared with MC included calcium (Ca), iron (Fe), zinc (Zn), copper (Cu), magnesium (Mg), selenium (Se), vitamins A, D, E, C, thiamin, riboflavin, and niacin. There were no differences in micronutrient intakes between FA and FC, nor were there any significant differences in serum trace element concentration. Serum Zn concentration was significantly higher in MA than MC, but the reverse was true for serum Cu and ferritin. Mean dietary intake of energy, PRO, and micro- nutrients met or exceeded current RDA/DRI recommendations by MA, but not MC. Mean intakes of Ca, Fe, and Zn were below RDA/DRI-recommended levels in both FA and FC. Serum trace element status for all groups was adequate despite lower than recommended RDA/DRI intakes of some nutrients. The results suggest that additional energy and micronutrient intake beyond RDA/DRI recommendations may not be necessary. However, intense or competitive sports activity may require additional energy and PRO intakes beyond the levels provided by current RDA/DRI recommendations.
Poortmans et al.112 examined postexercise proteinuria in females (n = 93) and males (n = 77) aged 6 to 18 years. Data collected included urine total protein (TP), albumin, retinol binding protein (RBP), β2 microglobulin (β2M), and creatinine. Urine samples were collected prior to and 30 minutes after completion of maximal exercise by the 20-meter shuttle run test.
Results indicated glomerulus permeability and tubular reabsorption increases with age, and excretion rates of all PRO components were related to absolute intensity of exercise (p<0.001).
Children aged 6 to 9 years demonstrated a gender difference in postexercise proteinuria with enhanced TP, albumin, β2M, and RBP excretion in males, but not in females. The authors concluded that post-exercise proteinuria is present at maximal exercise in childhood and adolescence, and magnitude of PRO excretion is strictly related to exercise intensity.
4. Fluid
Positive fluid balance is necessary for PA and athletic performance.113 Inadequate hydration increases body heat storage, decreases blood volume, and results in reduced exercise tolerance.114 Children have larger body-surface-area to mass ratios than adults, which, in extreme weather conditions of heat or cold result in greater heat loss or heat absorption, respectively. Additionally, thermoregulatory responses are less effective in children than in adults.115
Children, similar to adults, do not drink enough fluid to replace losses during PA especially in warm weather.116 Wilk and Bar-Or117 demonstrated a 44.5% increase of voluntary fluid intake in non-trained, non-acclimatized children intermittently exercising in a climatic chamber (35°C, 45%–50% relative humidity) by flavoring their water. An additional 45.5% increase in voluntary fluid intake was achieved by adding 6% CHO and 18 mmol/L NaCl to the flavored water. Voluntary fluid replacement prior to and during PA or sports participation may prevent hypo hydration or dehydration altogether.
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Rivera-Brown et al.118 examined the effect of tropical climate (wet bulb globe temperature 30°C
± 1.0°C) on voluntary drinking, drink composition, and fluid balance. Twelve heat-acclimatized male athletes aged 11 to 14 years (mean age 13.4 ± 0.4 years) participated in two 3-hour exercise sessions. Each session consisted of four 20-minute cycling bouts at 60% ·
VO2max alternating with 25-minute rest periods. One of two beverages [unflavored water (UFW) or flavored water plus 6%
CHO and 18 mmol/L NaCL (FWNaCl)] was offered ad libitum during each session. Flavor preferences were predetermined in each athlete. Beverages were then assigned in a random fashion, with each athlete receiving both beverages.
Fluid intake and losses along with serum osmolality, NaCL, hemoglobin, and hematocrit were collected initially and at the end of the study. BW was measured at the beginning and end of each exercise session. Analysis of data demonstrates a 32% higher (p<0.05) total intake of FWNaCl beverage than UFW. A pattern of hypohydration (0.94% of initial BW) was observed with UFW whereas euhydration (+0.18% of initial BW) was observed with FWNaCl (p<0.5). Despite a 5.5%
higher fluid intake than fluid losses with FWNaCl and a negative fluid balance with UFW, no differences were observed in serum volume, osmolality, or electrolyte concentration. These authors concluded that consumption of FWNaCl beverage prevents voluntary dehydration in heat-acclima- tized male athletes exercising in a tropical climate.