P ART I Nutritional Concerns of Athletes
CHAPTER 4 CHAPTER 4 Nutritional Concerns of Adolescent Athletes
B. Micronutrient Intake and Status
Inadequate energy intakes are generally accompanied by marginal macro- and micronutrient intakes. Indeed, in studies in which athletes reported consuming adequate energy, macro- and
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micronutrient intakes generally met or exceeded recommended levels.1,23 Conversely, in those studies in which athletes were consuming inadequate energy, macro- and micronutrient intakes typically failed to meet recommendations.1,8,15,24,30,33,35 For example, Berning et al.23 examined the energy and nutrient intakes of 22 male (15–18 years) and 21 female (12–17 years) swimmers and found that reported energy intakes of the athletes (5222 kcal/d and 3573 kcal/d for males and females, respectively) far exceeded those reported for the average teenager. In addition, the athletes’
average daily intakes of vitamins A and C, thiamin, riboflavin, niacin, calcium, and iron met or exceeded the respective RDA.23 Similarly, Rankinen et al.1 compared the dietary intake and nutri- tional status of 49 adolescent male (12–13 years) hockey players and 43 young adolescent female (11–12 years) gymnasts, figure skaters, and runners to that of 88 male and female, adolescent, non- athletic controls. On average, the male athletes consumed more energy, protein, thiamin, riboflavin,
Table 4.1 Self-Reported Energy Intakes of Adolescent Athletes
Reference Sport
No. of Subjects
Age Range
(yr.)
Mean Weight
(kg)
Mean Energy
Intake (kcal/d)
Mean Energy
Intake (kcal/kg/d) FEMALES:
Benson et al.1985 (30) Dance 92 12–17 46.8 1,890 40.8
Rucinski 1989 (33) Figure Skating 23 13–22 — 1,174 —
Zeigler 1998 (35) Figure Skating 21 11–16 50.3 1,781 35.4
Benson et al. 1990 (31) Gymnastics 11–13 12 1,544 39.4
Benardot 1989 (41) Gymnastics 22 11–14 — 1,706 —
Fogelhom et al. 1995 (167) Gymnastics 12 16–18 51.7 1,776 —
Figure Skating Loosli and Benson 1986
(168)
Gymnastics 97 11–17 43.2 1,838 42.5
Sundgot–Borgen 1996 (169) Rhythmic Gymnastics
12 14–20 42 1,703 41
Baer and Tapper 1992* (24) Running 12 15–17 51.1 1,778 41.5
Benson et al. 1990 (31) Swimming 11–13 18 1,892 39.5
Berning et al. 1991 (23) Swimming 10 15–18 58.2 3,573 61.4
Peron and Endres 1985 (15) Volleyball 26 13–17 — 1,799 —
Beals et. al.1999 (170) Volleyball 26 14–17 65.2 2,248 34.4
MALES:
Rucinski 1989 (33) Figure Skating 17 16–26 — 2,897 —
Hickson et al. 1987 (29) Football 46 11–14 60.9 2,523 41.4
Hickson et al. 1987 (29) Football 88 15–18 75.9 3,365 44.3
Rankinen et al. 1995 (1) Ice Hockey 48 12–13 44.1 2,448 56.7
Schemmel et al. 1988 (34) Running 14 11–14 — 2,541 66.0
Schemmel et al. 1988 (34) Running 4 15–18 — 2,736 50.0
Rico–Sanz 1998 (28) Soccer 119 14–18 67.2 3,785 —
Berning et al. 1991 (23) Swimming 22 15–18 77.2 5,222 67.6
Hawley and Williams 1991 (43)
Swimming 9 11–14 56.4 3,072 55.0
Van Erp Baart et al. 1989 (171)
Swimming 20 15–18 72.9 3,720 52.6
Horswill et al. 1990 (172) Wrestling 18 14–17 63.7 — 26.6*
Schemmel et al. 1988 (34) Wrestling 50 11–14 — 2,459 53.0
Schemmel et al. 1988 (34) Wrestling 20 15–18 — 2,703 44.0
Roemmich and Sinning 1997 (32)
Wrestiling 9 15.4** 58.0 — 24.7*
* values represent “during season”
** mean age; age range not reported
— value not reported
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niacin, vitamins C and E, calcium, iron, zinc, copper, and selenium than controls. The female athletes, on the other hand, had similar energy and nutrient intakes to the controls, and in most cases, intakes failed to meet the RDAs. Loosli and Benson8 found similar inadequate energy and nutrient intakes in 97 competitive female gymnasts 11–17 years of age. Self-reported mean energy intake was only 1838 kcal/d, and 22 gymnasts reported consuming ≤1500 kcal/d, which is consid- erably less than the RDA for sedentary adolescents.8 These low energy intakes were accompanied by inadequate micronutrient intakes, with between 41% and 80% of the gymnasts consuming <2/3 of the RDA for calcium, iron, zinc, folate and vitamin B6.8
Figure skating, like gymnastics, is a sport in which a low body weight is considered advanta- geous, and, thus, athletes participating in this sport frequently demonstrate restrictive eating behav- iors and subsequent inadequate micronutrient intakes.33,35,38 For example, Ziegler et al.35 examined the energy and nutrient intakes of 21 competitive adolescent female figure skaters (11–16 years).
Self-reported mean energy intake was only 1781 kcal/d (range 869 kcal/d-2401 kcal/d) and mean calcium and iron intakes were both <2/3 of the RDA. In a similar study of 23 young female figure skaters (13–22 years), Rucinski33 found mean self-reported energy intake to be only 1174 kcal/d (range 373 kcal/d–2554 kcal/d) and mean micronutrient intakes were consistently ≤50% of the RDA.33
Adolescent female runners also frequently report inadequate energy and nutrient intakes. Baer and Taper24 examined dietary intakes and training status of six amenorrheic and six eumenorrheic adolescent runners. There were no significant differences between the groups in terms of energy or micronutrient intakes and both groups had inadequate intakes of energy, calcium, magnesium, iron, and zinc.
It is interesting to note that, despite the low nutrient intakes frequently reported for adolescent athletes, nutritional status, as measured by blood levels of micronutrients, does not seem to be negatively affected. In the Rankinen et al.1 study, for example, zinc, copper, and iron status parameters were within normal ranges for the female athletes despite the self-reported inadequate intakes. Similarly, none of the female figure skaters in the Ziegler et al.35 study presented with iron deficiency anemia even though more than half of the athletes were consuming <2/3 of the RDA for iron. It should be noted, however, that serum ferritin was not measured in the Ziegler et al35 study; thus, some of the athletes may have been iron depleted.
The lack of an association between micronutrient intakes and status measures could be viewed as further evidence for under-reporting among female adolescent athletes. However, it should be noted that very few of the aforementioned studies monitored weight changes (to ascertain weight stability) and none provided an indication of the length of time that the athletes had been following their particular eating patterns. Adolescents are notorious for inconsistent and erratic eating patterns such that what they consume (or fail to consume) might vary greatly from week to week. Thus, the intakes reported in the aforementioned studies may very well be accurate. It also should be emphasized that clinical nutrient deficiencies can take several months or even years to develop, which may further explain why the inadequate nutrient intakes seen in these short-term studies did not correspond to clinical nutritional deficiencies. More studies assessing nutritional status as well as longitudinal studies to assess changes in nutritional status with training are desperately needed.
Failure to meet energy and nutrient requirements will impair athletic performance and negatively impact health. Some health consequences of inadequate energy and nutrient intakes include short stature and delayed puberty,39,40 electrolyte imbalances and dehydration,41-43 increased susceptibility to athletic injuries,44 menstrual dysfunction,24,45,46 decreased bone mineral density, and increased risk of stress fractures and premature osteoporosis.47–49 Thus, it is crucial that adolescents (and their parents) make every effort to meet the energy and nutrient requirements that accompany partici- pation in sport. The following sections will outline what is currently known with respect to the energy and nutrient needs of adolescent athletes.
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IV. ENERGY AND MACRONUTRIENT REQUIREMENTS A. Energy Requirements
Because there are so few well-designed studies on energy balance in adolescent athletes, it is difficult to state with confidence the energy requirements of this group.50 Nonetheless, it is generally accepted that regular exercise, particularly of an intense nature, will increase an adolescent’s energy requirements.50 It is well recognized that adult athletes have greater energy needs than their sedentary counterparts.50 It has been recommended that adult athletes consume 40–50 kcal/kg–1 or (1.8–2.2 times basal metabolic rate (BMR))50 Extrapolating from studies done on adult athletes, one can theorize that energy and macronutrient needs increase with exercise training in the ado- lescent athlete. Adolescent athletes not only need to meet demands of daily living and support growth and development, but they also need energy to support physical training, speed recovery from intense training, prevent injury, and maintain normal menstrual function.50
Only two studies have examined the effects of exercise training on energy balance in previously sedentary boys and girls and both used doubly labeled water to measure total daily energy expen- diture. Blaak et al.51 reported a 12% increase in total daily energy expenditure in obese boys cycling 5 days/wk for 45 min. at 55–67% Vo2max. Similarly, Eliekim et al.52 reported that total daily energy expenditure of formally sedentary girls was 15% higher than a sedentary control group (34.5 kcal/kg–1 vs. 32.2 kcal/kg–1, respectively) after 5 weeks of endurance-type training performed 5 days/wk. These training studies indicate that just 1 hour of moderate-intensity, endurance-type exercise performed 5 days/wk can significantly increase energy expenditure and, thus, energy requirements. Because most adolescent athletes easily exceed the duration, intensity, and frequency of the exercise bouts described in the above training studies, it is safe to assume that energy needs of adolescent athletes are substantially greater; exactly how much greater remains unknown. What is known is that energy requirements will be influenced by the energy demands of the specific sport, the athlete’s age and gender, and potential changes in energy intake and spontaneous physical activity associated with exercise training.50
It has been estimated that energy needs of moderately active adolescents may be 1.5–2.0 times greater than that for sedentary or “normally” active adolescents.8 However, this estimate was not based on actual measures of energy balance in active adolescents. The RDAs for “normally” active adolescent males and females are listed in Table 4.2. A recently published method for estimating increased energy needs in competitive sports uses the RDAs for energy with additional calories to reflect increased energy demands of athletes in training.53 For example, using this method, a weight- stable 11–14-year-old female athlete training rigorously would require an additional 5 kcal per lb (2.3 kcal/kg), while a 15–18-year-old female athlete would require an additional 4 kcal per lb (1.8 kcal/kg).
Table 4.2 The Recommended Dietary Allowances for Energy and Protein for Adolescents Gender Age (yr)
Energy Intake (kcal/kg/d)
Protein Intake (kcal/kg/d)
Males 11–14 55 1.0
15–18 45 0.9
Females 11–14 47 1.0
15–18 40 0.8
* Adapted from Reference 21 8199/C04/frame Page 64 Thursday, August 10, 2000 3:41 AM
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