Atypical BMI Trajectory Detectable in Children as Early as Age 3.5 Years

THURSDAY, June 5, 2025 (HealthDay News) — Children on the path to obesity can be detected as early as age 3.5 years, according to a study published online May 22 in JAMA Network Open.

Chang Liu, Ph.D., from Washington State University in Pullman, and colleagues examined how early-life factors are associated with body mass index (BMI) trajectories in children. The analysis included participants in the Environmental influences on Child Health Outcomes cohort, which included children aged 1 to 9 years (January 1997 to June 2024).

The researchers identified two distinct two-phase BMI patterns. The typical group (89.4 percent) showed linear decreases in BMI, with the lowest BMI at age 6 years, followed by linear increases from 6 to 9 years (mean BMI at 9 years: 17.33 kg/m²). The atypical group (10.6 percent) showed a stable BMI from ages 1 to 3.5 years, followed by rapid linear increases from ages 3.5 to 9 years and a mean BMI at age 9 years of 26.2 kg/m², which exceeded the 99th percentile. Risk factors associated with the atypical trajectory included prenatal smoking, high prepregnancy BMI, high gestational weight gain, and high birth weight.

“The fact that we can identify unusual BMI patterns as early as age 3.5 shows how critical early childhood is for preventing obesity,” Liu said in a statement. “Our findings suggest there are important opportunities to reduce childhood obesity, such as helping pregnant women quit smoking and manage healthy weight gain, as well as closely monitoring children who show early signs of rapid weight gain.”

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