Adolescence is the period of transition between childhood and adulthood. This reflects not only the physical and emotional changes experienced by the adolescent, but the development of dietary behaviors. Whereas younger children are characterized by their resistance to new experiences, the adolescent may use food to assert their independence, not always in a beneficial way. This section will cover development in adolescence and highlight nutrients that are important during this time. Information on adolescent energy and nutrient intakes from a broad range of countries will be presented. The findings will be put in context with dietary recommendations.
Physical Changes During Adolescence Adolescence is generally assumed to be the period of human development from 10 to 18 years of age, a time during which rapid growth and physical maturity take place.
It is not fully known when growth ceases. Certainly, height gains of up to 2 cm can still occur between 17 and 28 years. Important nutrients for growth include protein, iron, calcium, vitamin C, vitamin D, and zinc. Calcium, in particular, has a key role in bone development, and huge increments in bone density are seen during adolescence under the influence of sex hormones. Bone density peaks in the early twenties and a low bone density at this time is related to increased osteoporosis risk in later life, especially for women. Studies have suggested that body mass index in adolescence is the best predictor of adult bone density, explaining why children who experience anorexia nervosa are likely to have a higher risk of osteoporosis.
Adipose stores There are few differences in body fat between boys and girls in the prepubertal stage. However, during puberty, girls develop adipose tissue at a greater rate than boys, laying down stores in the breast and hip regions. The pattern for boys is rather different and tends towards a more central deposition. Methods for estimating fatness in adolescents include weight for height, body mass index (weight in kilograms/height in meters2), skinfold thickness measures, bioelectrical impedance analysis, densitometry, magnetic resonance imaging, dual energy X-ray absorptiometry, and computer tomography. Waist circumference is gaining popularity as a useful proxy of fatness in the field. Many researchers argue that it is a better predictor than body mass index (BMI) of the central adipose stores, which place the individual most at risk from later obesity, diabetes, and coronary heart disease.
Sexual Development In girls, the onset of menarche at around 13 years is triggered by the attainment of a specific level of body fat, with taller, heavier girls more likely to experience an early menarche. Vigorous exercise, e.g., gymnastics and endurance running, can delay the menarche, due both to the physiological effects of regular training and the depletion of body fat. Iron becomes more important for girls as menstrual periods become regular and heavier, and there is evidence that the iron status of many girls may be inadequate. Low iron status in this age group is, in part, due to higher requirements, but it is also linked to nutritional practices such as missing breakfast, avoiding red meat, and dieting.