Body composition during the first 2 years of life: An updated reference

Normative body composition during the first 2 y of life was derived from a prospective study of 76 children. We present I) fat free mass (FFM) and its components, and fat mass (FM), 2) incremental growth rates partitioned int o chemical components, and 3) age-specific and gender-specific constants fo r converting chemical and physical components into FFM for children during the first 2 y of life. A multicomponent model based on measurements of tota l body water (TBW), total body potassium (TBK) and bone mineral content (BM C) was used to estimate FFM and FM at 0.5, 3, 6, 9, 12, 18, and 24 mo of ag e, TBW was determined by deuterium dilution, TBK by whole body counting, an d BMC by dual energy x-ray absorptiometry. FFM was higher in boys than girl s between 0.5-18 mo of age (p less than or equal to 0.05). Percent FM incre ased on average from 13 to 31% between 0.5 and 3-6 mo, and then gradually d eclined. Percent FM was significantly higher in girls than in boys at 6 and 9 mo of age (p less than or equal to 0.02). The components of FFM on a per centage basis changed with age (p = 0.001), but not gender. The protein con tent of FFM increased gradually with age, while TBW declined (p = 0.001). A s a percentage of FFM, osseous mineral increased from 2.0 to 3.4% in boys a nd from 2.1 to 3.3% in girls between 0.5 and 24 mo (p = 0.001). Density and potassium content of FFM increased gradually with age (p = 0.001). These n ormative body composition data provide an updated reference upon which to a ssess normal growth and nutritional status of pediatric populations represe ntative of mixed feeding groups during the first 2 y of life.