Original Investigation August 17, 2020 JAMA Pediatr. 2020;174(12):1141-1148. doi:10.1001/jamapediatrics.2020.2673 Key Points Question Is a rapid increase in fat mass percentage in early life associated with higher trajectories of body fat mass during the first 2 years of life? Findings In a cohort study of 401 infants, only the change in fat mass percentage during the first 6 months of life was associated with fat mass percentage and abdominal subcutaneous fat mass at age 2 years.