Dietary Intake, Anthropometric Characteristics, and Iron and Vitamin D Status of Female Adolescent Ballet Dancers Living in New Zealand.

Ballet dancing is a multifaceted activity requiring muscular power, strength, endurance, flexibility, and agility; necessitating demanding training schedules. Furthermore dancers may be under aesthetic pressure to maintain a lean physique, and adolescent dancers require extra nutrients for growth and development. This cross-sectional study investigated the nutritional status of 47 female adolescent ballet dancers (13-18 years) living in Auckland, New Zealand. Participants who danced at least 1 hr per day 5 days per week completed a 4-day estimated food record, anthropometric measurements (Dual-energy X-ray Absorptiometry) and hematological analysis (iron and vitamin D). Mean BMI was 19.7 ± 2.4 kg/m2 and percentage body fat, 23.5 ± 4.1%. The majority (89.4%) of dancers had a healthy weight (5th-85th percentile) using BMI-for-age growth charts. Food records showed a mean energy intake of 8097.3 ± 2155.6 kJ/day (48.9% carbohydrate, 16.9% protein, 33.8% fat, 14.0% saturated fat). Mean carbohydrate and protein intakes were 4.8 ± 1.4 and 1.6 ± 0.5 g/kg/day respectively. Over half (54.8%) of dancers consumed less than 5 g carbohydrate/kg/day, and 10 (23.8%) less than 1.2 g protein/kg/day. Over 60% consumed less than the estimated average requirement for calcium, folate, magnesium and selenium. Thirteen (28.3%) dancers had suboptimal iron status (serum ferritin (SF) < 20 µg/L). Of these, four had iron deficiency (SF < 12 µg/L, hemoglobin (Hb) ≥ 120 g/L) and one iron deficiency anemia (SF < 12 µg/L, Hb < 120 g/L). Mean serum 25-hydroxy vitamin D was 75.1 ± 18.6 nmol/L, 41 (91.1%) had concentrations above 50 nmol/L. Female adolescent ballet dancers are at risk for iron deficiency, and possibly inadequate nutrient intakes.

Carbohydrate availability and muscle energy metabolism during intermittent running.

PURPOSE: To examine the influence of ingesting a carbohydrate-electrolyte (CHO-E) solution on muscle glycogen use and intermittent running capacity after consumption of a carbohydrate (CHO)-rich diet. METHODS: Six male volunteers (mean +/- SD: age 22.7 +/- 3.4 yr; body mass (BM) 75.0 +/- 4.3 kg; V O2 max 60.2 +/- 1.6 mL x kg(-1) x min(-1)) performed two trials separated by 14 d in a randomized, crossover design. Subjects consumed either a 6.4% CHO-E solution or a placebo (PLA) in a double-blind fashion immediately before each trial (8 mL x kg(-1) BM) and at 15-min intervals (3 mL x kg(-1) BM) during intermittent high-intensity running to fatigue performed after CHO loading for 2 d. Muscle biopsy samples were obtained before exercise, after 90 min of exercise, and at fatigue. RESULTS: Subjects ran longer in the CHO-E trial (158.0 +/- 28.4 min) compared with the PLA trial (131.0 +/- 19.7 min; P < 0.05). There were no differences in muscle glycogen use for the first 90 min of exercise (approximately 2 mmol of glucosyl units per kilogram of dry matter (DM) per minute). However, there was a trend for a greater use in the PLA trial after 90 min (4.2 +/- 2.8 mmol x kg(-1) DM x min(-1)) compared with the CHO-E trial (2.5 +/- 0.7 mmol x kg(-1) DM x min(-1); P = 0.10). Plasma glucose concentrations were higher at fatigue in the CHO-E than in the PLA trial (P < 0.001). CONCLUSIONS: These results suggest that CHO-E ingestion improves endurance capacity during intermittent high-intensity running in subjects with high preexercise muscle glycogen concentrations. The greater endurance capacity cannot be explained solely by differences in muscle glycogen, and it may actually be a consequence of the higher plasma glucose concentration towards the end of exercise that provided a sustained source of CHO for muscle metabolism and for the central nervous system.