Longitudinal fat mass and visceral fat during the first 6 months after birth in healthy infants: support for a critical window for adiposity in early life.

INTRODUCTION: Body composition in early life influences the development of obesity during childhood and beyond. It is, therefore, important to adequately determine longitudinal body composition during the first months of life. PATIENTS AND METHODS: In 203 healthy term infants, we investigated longitudinal body composition, including fat mass percentage (FM%) and fat-free mass (FFM), by air-displacement plethysmography, at 1, 3 and 6 months of age and abdominal visceral fat and abdominal subcutaneous fat, by ultrasound, at 3 and 6 months. RESULTS: We found a significant increase in FM% between 1 and 3 months but not between 3 and 6 months (p < 0.001, p = 0.098, respectively). Girls had higher FM% than boys at 1 and 6 months (p = 0.05, p < 0.001 respectively) and less FFM than boys at 1, 3 and 6 months (p = 0.02, p = 0.02, p < 0.001, respectively). There was a large variation in FM% at all ages even between infants with similar weight standard deviation scores. Visceral fat and abdominal subcutaneous fat did not change between 3 and 6 months. FM% was highly correlated with abdominal subcutaneous fat but not with visceral fat. CONCLUSION: Changes in FM% occur mainly in the first 3 months of life, and FM%, visceral and abdominal subcutaneous fat do not change between 3 and 6 months, supporting the concept of a critical window for adiposity development in the first three months of life. In addition, our study provides longitudinal reference data of FM%, FFM, visceral fat and abdominal subcutaneous fat during the first 6 months of life.