Objective: To examine the relationship between body composition-specifically fat mass (FM) and fat-free mass (FFM)-in early infancy, and mental health outcomes in early childhood.

Study design: In the Infant Anthropometry and Body Composition birth cohort study from Ethiopia, body composition was measured at birth and 1.5, 2.5, 3.5, 4.5, and 6 months of age. Mental health was assessed at 5 years of age using the approved Amharic version of the Strengths and Difficulties Questionnaire (SDQ), a parent report scale covering 4 different domains providing a total difficulties score. The associations of FM or FFM at birth as well as during early infancy, with SDQ score at 5 years of age were examined using multiple linear regression analyses.

Results: At 5 years of age, the mean ± SD for SDQ score was 10.4 ± 5.8. FM at birth was positively and FFM negatively associated with SDQ score. For each kg increase in FM at birth, the SDQ score at 5 years was 5.7 points higher (β = 5.7; 95% CI, 1.4-10.0). In contrast, for each kilogram increase in FFM at birth, the SDQ score was 3.9 points lower (β = -3.9; 95% CI, -7.0 to -0.8). Neither FM nor FFM accretion rate during early infancy were associated with SDQ score at 5 years of age.

Conclusions Fetal rather than infant body composition was associated with SDQ score at 5 years of age. Greater FFM accretion during fetal life may have contributed to more optimal neurobehavioral development during early life. However, the potential mechanisms underlying the observed associations need further investigation.