Submitted to: Pediatric Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/14/2000
Publication Date: N/A
Citation: Interpretive Summary: During the first 2 years of life, human beings experience significant growth-related changes in body size and composition. It is important for doctors to have a body composition standard by which to judge whether a baby is growing properly, being fed appropriately, or responding well to medicine. Body composition methods used in adults are not applicable to children. The classic Fomon article on children's body composition, published in 1982, has been widely used as a reference, but it has major limitations, including the lack of data pertaining to certain chemical components. We performed the first longitudinal study on body composition during the first 2 years of life. We recruited 76 children, 72 of whom completed the study. We present data on fat-free mass and its components, and fat mass; growth rates partitioned into chemical components; and age- and gender-specific constants for converting chemical components into fat-free mass during the first 2 years of life. Our data differ from those of the Fomon reference in presenting total body water, total body potassium and bone mineral content. Our new body composition data provide a contemporary reference that can be used to assess a baby's normal growth and nutritional status from birth to age 2. We believe the use of our conversion figures in determining fat-free mass will improve the accuracy of pediatric body composition methods.
Technical Abstract: Normative body composition during the first 2 y of life was derived from a prospective study of 76 children. We present 1) fat free mass (FFM) and its components, and fat mass (FM); 2) incremental growth rates partitioned into chemical components; and 3) age- and gender-specific constants for converting chemical components into FFM for children during the first 2 y of life. A multicomponent model based on measurements of total body water (TBW), total body potassium (TBK) and bone mineral content (BMC) was used to estimate FFM and FM at 0.5, 3, 6, 9, 12, 18 and 24 mo of age. TBW was determined by deuterium dilution, TBK by whole body counting, and BMC by dual energy x-ray absorptiometry. FFM was higher in boys than girls at 0.5 mo (P=0.056) and between 3-18 mo of age (P lesser than or equal to 0.03). Percent FM increased abruptly from 11 to 31% between 0.5 and 3-6 mo, and then gradually declined. Percent FM was significantly higher in girls than boys at 6, 9 and 18 mo of age (P lesser than or equal to 0.02). The components of FFM on a percentage basis changed with age (P=0.001), but not gender. The protein content of FFM increased gradually with age, while TBW declined (P=0.001). As a percentage of FFM, osseous mineral increased from 2.0% to 3.4% in boys and from 2.1% to 3.3% between 0.5 mo to 24 mo (P=0.001). Density and potassium content of FFM increased gradually with age (P=0.001). These normative body composition data provide a reference upon which to assess normal growth and nutritional status during the first 2 y of life.