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close this bookActivity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)
close this folderAssessment and significance of body composition in infants and children
View the document(introductory text...)
View the documentAbstract
View the document1. Techniques for estimating body composition
View the document2. Changes in body composition during growth
View the document3. The companionship of lean body mass and fat
View the document4. Maintenance energy need is related to body size and composition
View the document5. The energy cost of weight gain
View the documentAcknowledgements
View the documentReferences
View the documentDiscussion (summarized by A. Ferro-Luzzi)

2. Changes in body composition during growth

While girls are only slightly fatter than boys at birth and throughout infancy and childhood, the sex difference in body composition becomes significant during adolescence. The adolescent spurt in weight and stature is accompanied by increases in lean body mass (LBM) and body fat; the boy acquires considerably more LBM than the girl, while she accumulates a larger percent body fat. Between the age of 10 and 20 years, the average boy puts on 33 kg LBM, the average girl only 16 kg. This sex difference remains when LBM is referred to stature: adolescent boys have a higher LBM:height ratio than girls. Not only is the adolescent spurt in LBM more intense in the male, but it also lasts longer; maximum LBM is achieved by the girl at about 18 years, but in the boy not until about age 20 (Figure 2).

Figure 2. Upper section: Mean body weight and lean body mass (LBM) during late childhood and adolescence. Lower section: Estimated LBM velocity; note the more intense and prolonged LBM spurt in boys. Author's data by potassium-40 counting.

This sex difference in LBM growth has obvious nutritional implications. Based on available data, the average boy will accumulate during the second decade of life 770 g Ca, 2.08 g Fe, 0.98 g Zn, and 7300 g protein. For the average girl these values are much less, namely 400 g Ca, 0.84 g Fe, 0.66 g Zn, and 3650 g protein. The sex difference is similarly striking for the estimated daily increments in body content at the peak of the adolescent growth spurt: 400 mg Ca for the boy versus 240 mg for the girl, 3.8 g protein for the boy, 2.25 g for the girl.