A large population-based study suggests that body mass index (BMI) at age six is a stronger predictor of overweight and obesity in early adulthood than BMI measurements taken at ages two, ten, or fourteen. Researchers also found that children with elevated BMI at age two who experienced slower BMI growth between ages two and six had a risk profile similar to that of children with average BMI.

The study was conducted as part of the Generation R project, a long-term cohort study that has followed participants from fetal development into adulthood. Investigators analyzed data from 3,528 children born in the Netherlands between 2002 and 2006. Participants had information available on birth weight, gestational age, childhood BMI measurements, and BMI assessments at approximately 18 years of age.

Children were grouped according to age- and sex-adjusted BMI scores and categorized into low, middle, and high BMI tertiles. Researchers also examined growth patterns during four developmental periods: birth to age two, ages two to six, six to ten, and ten to fourteen years.

The findings showed that overweight or obesity persisted into young adulthood for 32.6% of children who were overweight at age two, 54.0% at age six, 57.4% at age ten, and 70.3% at age fourteen. More than two-thirds of these individuals had a recurring history of excess weight during childhood.

Each one-unit increase in BMI standard deviation score at age six was linked to more than double the likelihood of being overweight or obese at age 18. Birth weight was also associated with future weight status, although the relationship was considerably weaker.

Children with average or high birth weight who experienced rapid BMI growth during the first two years of life were more likely to develop overweight later on. Accelerated BMI growth between ages two and six, as well as between six and ten years, independently increased the risk of overweight and obesity regardless of a child's BMI category. The highest risk was observed among children in the highest BMI group at age ten who also experienced accelerated growth.

Importantly, children who had a high BMI at age two but showed slower BMI growth between ages two and six demonstrated a risk of overweight and obesity comparable to that of peers with average BMI.

The researchers concluded that identifying and improving unhealthy BMI trajectories early in childhood may provide an important opportunity to prevent overweight and obesity in adulthood.

The study was led by Jasmin M. de Groot and colleagues from the Generation R Study Group at Erasmus MC University Medical Center Rotterdam and was published online in the European Journal of Pediatrics on May 21, 2026.