Age trends in fat in normal and obese children

Body density was determined in 151 normal boys and girls 9–17 years old by hydrostatic weighing and simultaneous determination of residual lung volume by the nitrogen dilution method. Also, 56 obese children 9–15 years old were studied. Body composition changed characteristically in the groups of normal children. In boys, density at 9 years was 1.062 (S.E. = 0.003) and fell to 1.048 (S.E. = 0.004) at 11–13 years; it rose to 1.073 (S.E. = 0.002) at 16, indicating a relative decrease in fat content and increased development of lean body mass. In girls, values were more stable-1.041–1.042 (S.E. = 0.003–0.004) on the average, except in the year 13–14 when body density increased to 1.051 (S.E. = 0.004). After the start of clinical puberty, body density again fell to 1.038 (S.E. = 0.003) indicating increased fat content. There was significant sexual difference in body density before the beginning of prepuberal acceleration of growth and later with the start of clinical puberty. Body density for obese boys 9–12 years old was 1.010 (S.E. = 0.002) and for obese girls of the same age 1.009 (S.E. = 0.002). In 13–15-year-old obese boys, density was 1.016 (S.E. = 0.003) and for girls was 1.012 (S.E. = 0.0039); i.e. in obese children no sex or age differences in body density were found. Submitted on May 9, 1960