Metabolism: clinical and experimental
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Body fat, fat cell size, and fat cell number were determined in a longitudinal study on 16 normal-weight infants during the age period 1-18 mo. The methods used included whole-body counting of 40K for determination of body fat and adipose tissue biopsies. A new method of calculation of body fat in infants is presented. ⋯ From 1 to 12 mo of age the expansion of body fat was explained by and increase in fat cell size, while in the age period 12-18 mo it was mainly due to an increase in fat cell number. At 18 mo lthe fat cell size was the same as in 8-yr-old girls and 22-yr-old women (normal-weight females previously studied). The fat cell number at 18 mo, however, was far below the number at 8 yr of age, as well as the still higher number of the 22-yr-old women.