Normative Data for Lean Mass and Fat Mass in Healthy Predominantly Breast-Fed Term Infants From 1 Month to 1 Year of Age

Background: A leaner body phenotype in infancy plays an important role in the early life prevention of obesity. However, there is a dearth of reference data for body composition in infancy. This study aimed to create a normative reference dataset for lean (LM) and fat (FM) mass and accretion rates in healthy infants. Methods: Healthy term-born infants (35 boys; 35 girls) were studied at ≤ 1, 3, 6, 9, and 12 mo of age for growth and compared to World Health Organization standards. LM (g) and FM (g) were measured using DXA (APEX version 13.3:3, Hologic 4500A) in infant whole-body mode. Sex specific reference curves were generated using the LMS method (LMSchartmaker, Medical Research Council, UK). Results: Infants were predominantly white (82.9%), breastfed (98.4% ≥ 3 mo), and grew in length and weight within World Health Organization Z-score ranges for normal growth across infancy. LM accretion was 327.4 ± 12.5 g/mo representing 95% increment in LM. Boys had more LM compared to girls at 12 mo (7807.4 ± 1114.0 vs 6817.4 ± 1016.1 g; p = 0.008). FM accretion was 114.3 ± 12.0 g/mo representing 114% increment in FM with no difference between the sexes. Conclusions: This data, which is based on a healthy sample of infants, characterizes LM and FM accretion during the first year of life and will aid in the interpretation of body composition.