Exploring Patterns of the Body Mass Index Trajectory in Japanese Children

Background: Childhood overweight and obesity are health problems worldwide. Understanding the variations in growth patterns, while considering body size in children, is essential to determine the optimal time for initiating interventions to control body size. Here, we aimed to conduct an explorative analysis for identifying the variations in the developmental patterns of body size in Japanese children.

Methods: The data comprised details of 1,536 children (749 boys, 787 girls) born between 2004 and 2010 in Japan. We used a discrete mixture model to explore the patterns of body mass index (BMI) trajectories. The BMI was calculated as weight (kg)/height (m ²) and standardized by using the z-score; it was measured at birth and then annually between the ages of 6 and 14 years.

Results: Five patterns of BMI trajectory were identified among boys and 6 patterns were identified among girls. For example, overweight boys were found to be divided into 3 types—i.e., those maintaining severe overweight (3.3%), maintaining slight overweight (7.9%), or gradually becoming overweight at 8-year-old(18.5%). Conversely, overweight girls were found to be divided only into 2 types, which were similar to 2 patterns (maintaining severe overweight or slight overweight) observed in boys.

Conclusion: As many overweight children were already overweight at their preschool age, intervention programs should target overweight preschoolers. Children who are not overweight but who show a gradual increase in their BMI during preschool should also be targeted by early intervention programs, as they could become overweight after reaching school age.