Objective: The objective of this study was to identify subgroups with distinct fat and fat-free growth patterns in the first 6 months of life and describe predictors of these different patterns.

Methods: A total of 510 apparently healthy Ethiopian infants were followed from birth to 6 months of age. Each infant had at least three and up to six repeated measurements of fat and fat-free mass using air-displacement plethysmography. Latent class trajectory analyses were used to categorize infants in groups with distinct body composition patterns.

Results: Four distinct fat mass and two fat-free mass growth patterns were identified. Of the infants measured, 5% presented a delayed fat growth pattern and 3% presented a catch-up fat growth pattern involving low birth weight but a significant fat growth velocity from 2.5 to 6 months. A large class had a high fat level at birth and an accelerated fat growth pattern in early infancy. Fat-free growth was represented by two distinct classes with less variability. Catch-up growth was primarily seen in fat mass.

Conclusions: We identified distinct patterns of delayed, catch-up, and accelerated fat growth in early infancy. This variability is not detected in regular anthropometric assessment and could be a mechanism linking early growth with later obesity and cardiometabolic risk.