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-specific and gender-specific constants for converting chemical and physical 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 between 0.5-18 mo of age (p < or = 0.05). Percent FM increased on average from 13 to 31% between 0.5 and 3-6 mo, and then gradually declined. Percent FM was significantly higher in girls than in boys at 6 and 9 mo of age (p < or = 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% 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 normative body composition data provide an updated reference upon which to assess normal growth and nutritional status of pediatric populations representative of mixed feeding groups during the first 2 y of life.

Infant feeding mode is associated with differences in body composition in early infancy which do not persist into the second year of life.

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Background: Metabolic adjustments occur during pregnancy and lactation to support fetal growth and milk synthesis; however, the effect of body composition and hormonal milieu on these changes is poorly understood. Objective: We hypothesized that energy metabolism changes during pregnancy and lactation to support fetal growth and milk synthesis, and that body composition and hormonal milieu influence these alterations. Design: We measured energy expenditure, body composition, and hormone, metabolite, and catecholamine concentrations in 76 women (40 lactating, 36 nonlactating) at 37 wk gestation and 3 and 6 mo postpartum. Total energy expenditure (TEE), basal metabolic rate (BMR), sleeping metabolic rate (SMR), and minimal SMR (MSMR) were measured with room calorimetry. Fatfree mass (FFM) and fat mass were estimated with a 4-component model. Results: TEE, BMR, SMR, and MSMR were 15-26% higher during pregnancy than postpartum after being adjusted for FFM, fat mass, and energy balance. TEE, SMR, and MSMR were higher in lactating than in nonlactating women. Fasting serum insulin, insulin-like growth factor I, fatty acids, and leptin, and 24-h urinary free norepinephrine, epinephrine, and dopamine correlated positively with TEE, BMR, SMR, and MSMR. In nonlactating women, the respiratory quotient decreased over time, carbohydrate oxidation decreased, and fat oxidation increased. Substrate utilization was not influenced by body composition, fasting serum hormones, or 24-h urinary catecholamines. Conclusions: These results indicate increased energy expenditure and preferential use of carbohydrates during pregnancy and lactation. Elevated respiratory quotient and carbohydrate utilization during pregnancy continue during lactation, consistent with preferential use of glucose by the fetus and mammary gland. Am J Clin Nutr 1999;69:299-307.