BODY-COMPOSITION DURING ADOLESCENCE - METHODS, LIMITATIONS AND DETERMINANTS

To some extent body composition reflects nutritional status. It is als o influenced by age, sex, race, physical activity and disease. The met hod used to measure body composition depends on the variable to be qua ntified. It may also depend on the practical conditions of the study. Detailed methods, such as densitometry, isotope dilution and electrica l impedance give more accurate information, but they are commonly base d on hypotheses established in adults. Anthropometric measurements can be used directly or as ratio or regression equations. At adolescence, the weight/height2 or body mass index (BMI) is preferred to weight fo r height as age is taken into account. In addition, the BMI pattern re flects real changes in body shape, and early in life it is an indicato r of later development. In addition to measuring weight and height ski nfold (SF) measurements should be carried out. The triceps SF is usual ly recommended and widely used as it is better than the subscapular SF to predict percent body fat. Trunk SFs, such as the subscapular, are better than extremity SF for their association with internal fat and t heir good correlations with risk factors and response to nutritional i nterventions. Chemical changes in the body are observed during growth. Chemical maturity does not occur until after puberty, but most change s occur early in life. Tracking is the maintenance of an individual in the same percentile range across age and varies according to the grow th parameter and to the period of growth. Low tracking of fatness (up to the age of 8 years) corresponds to the period of rapid chemical cha nges. Low tracking of stature is observed at adolescence when height v elocity is high. Nutrition affects fatness and stature, but the conseq uences of under- and over-nutrition differ between early childhood and adolescence. BMI curves show that most changes have their origin duri ng the first years of life.