Body Fat and Bone Mineral Content of Infants Fed Breast Milk, Cow's Milk Formula, or Soy Formula During the First Year of Life

Objective: To characterize growth, fat mass (FM), fat-free mass (FFM), and bone mineral content (BMC) longitudinally in healthy infants fed breast milk (BM), cow's milk formula (CMF), or soy formula (SF) during the first year of life.

Study Design: Infants were assessed at age 3, 6, 9, and 12 months. Growth was evaluated using standard anthropometric techniques, and body composition was assessed by dual-energy X-ray absorptiometry. Mixed-effects models with repeated measures were used, adjusting for race, socioeconomic status, gestational age, birth weight, birth length, sex, age, and diet history.

Results: Compared with infants fed formulas, infants fed BM had higher FM at age 3 months, and lower FFM at age 6-12 months (P < .001). Infants fed SF had greater FFM at age 6 months and 9 months compared with infants fed CMF (P < .001). BMC was higher in infants fed BM and lower in infants fed SF at age 3 months (P < .001), but by age 12 months, BMC was significantly higher in infants fed SF.

Conclusion: Infants fed CMF and SF had significantly different fat and bone accretion trajectories, and all infants fed formula were significantly different from infants fed BM. Infants fed SF had a leaner body phenotype throughout the first year of life, lower bone mineralization by age 3 months, and greater bone mineral accretion during the first year of life compared with infants fed BM or CMF. Although the body composition profiles are strikingly different in these 3 diet groups, the implications for long-term health outcomes and bone health remain unclear.