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Developmental pathways leading to obesity in childhood

Publication: Health Reports 2009:20(3)

Authors: Samar Hejazi, V. Susan Dahinten, Sheila K. Marshall and Pamela A. Ratner

Data: National Longitudinal Survey of Children and Youth cycles 2 through 5 (1996/1997 to 2002/2003)

This study identifies age-related patterns of overweight and obesity from toddlerhood to childhood in a representative sample of Canadian children.

Trajectories of body mass index (BMI) over six years, starting at ages 24 to 35 months, identified four groups of girls:  stable normal BMI, early declining BMI, late declining BMI, and an accelerating rise to obesity, and three groups of boys: stable normal BMI, transient high BMI, and a J-curve rise to obesity.

Girls’ trajectory groups

The majority of the girls (64%) were in the “stable normal BMI” group.  Throughout the six years, their average BMI was normal for their age and sex.

Another 8% of the girls, the early-declining BMI” group, were in the obese category at the first two measurements (1996/1997 and 1998/1999), but by the third measurement (2000/2001) were within normal range and remained there at the fourth (2002/2003) when they were around eight years old.

Fourteen percent of the girls were in the “late declining BMI” group.  Their average BMI was above the overweight cut-off at the first two measurements, obese at the third, and within normal range at the fourth.

“Accelerating rise to obesity” was the label given to the remaining 14% of the girls. From normal at the first measurement, their average BMI rose to overweight at the second, and at the third, to obesity, which was sustained at the fourth.

Boys’ trajectory groups

The majority of the boys (70%) were in the “stable normal BMI” group.  Their average BMI was within the normal range throughout the six years.

Another 19% of the boys were in the “transient high BMI” group—their average BMI changed continuously across the four measurements.  Their BMI was within the normal range at the first measurement, overweight at the second, obese at the third, but within the normal range at the fourth.

Finally, 11% of the boys were in the “J-curve rise to obesity” group.  They were overweight at the first measurement, in the normal BMI range at the second, overweight at the third, and by the fourth, obese.