Slowing BMI in Youth Could Prevent Obesity

Laird Harrison

December 20, 2017

Slowing body mass index (BMI) growth in adolescence and early adulthood could prevent obesity in many adults, researchers say.

"[M]aintaining normal BMI rates in youth is crucial to preventing later overweight and obesity," write Marie-Jeanne Buscot, MSc, from the Menzies Institute for Medical Research, University of Tasmania, Australia, and colleagues in an article published online December 19 in Pediatrics.

Interventions should start in early childhood, but adolescence offers a "critical window for secondary prevention," the authors found.

Several previous studies have shown that people who are overweight in their childhoods are at a high risk for cardiovascular disease and type 2 diabetes in adulthood. And as obesity is so hard to reverse, researchers have emphasized the importance of preventing it.

But few studies have tracked the development of BMI all the way from early childhood to midadulthood.

To fill that gap, the researchers analyzed BMI data from the Cardiovascular Risk in Young Finns Study and included BMI measurements taken up to eight times over the course of 31 years, starting in 1980.

They included 2717 participants, 1252 boys and 1465 girls, who were ages 3 to 18 years in 1980. The researchers defined overweight as a BMI at least 25 kg/m2 and obese as a BMI at least 30 kg/m2.

By this definition, 8.4% of the participants (9.1% of the boys and 6.7% of the girls) were obese or overweight at baseline. At their latest assessment, 19.8% were obese.

The researchers divided the participants into four groups:

  • Group I, the reference group, had normal BMI in youth and were not obese in adulthood.

  • Group II, the high-BMI resolving group, were overweight or obese as youth but not obese as adults.

  • Group III, the high-BMI persisting group, were overweight or obese as youth and obese in adulthood.

  • Group IV, the incident obese group, had normal BMI in youth but became obese as adults.

Compared with the reference group, boys in the incident obese group had a 0.8 higher BMI at age 6 years (standard deviation [SD], 0.4 for girls and 0.3 for boys).

Compared with the high-BMI persisting groups, the high-BMI resolving group had average initial BMI levels that were 2.0 lower for boys (SD, 0.6) and 3.4 lower for girls (SD, 0.8).

The high BMI resolving group began to reach a plateau in BMI growth at an earlier age than the reference group. In the high BMI resolving group, girls began to reach a plateau at 16.1 years (SD, 1.4) and boys at age 21.4 years (SD, 1.7). In the reference group, girls began to reach a plateau at age 17.2 years (SD, 0.3) and boys at age 24.1 years (SD, 0.4). But the high-BMI resolving participants remained overweight on average into adulthood.

In contrast, the incident obese began to reach their plateaus at about age 30 years, and the high-BMI persisting group at about 25 years.

Compared with the reference group, the BMI rate of change among the incident obese group was 17% in boys and 14% in girls; they remained on this trajectory until about age 30 years. The women in this group, however, had higher BMI levels by midadulthood.

"Secondary interventions targeting the control of obesity progression in overweight older youth (ie, slowing down the increase in BMI yearly rates to stabilize weight) may contribute to reducing the incidence of adult obesity," the authors conclude.

The study makes an important contribution to the understanding of obesity trajectories from early childhood to midadulthood, write Cynthia L. Ogden, PhD, from the Centers for Disease Control and Prevention in Hyattsville, Maryland, and colleagues in an accompanying commentary.

Although it largely confirms previous findings about the correlation of obesity in childhood and adulthood, "The unique contribution of the Buscot study is that the rate of BMI change in both childhood and early adulthood and the estimated age at which BMI begins to plateau (or the increases in BMI begin to slow) were associated with the final, adult BMI."

However, they note some limitations: About two thirds of adults with obesity did not have obesity as a child or adolescent, they say, suggesting that weight gain in adulthood is also an important factor in the prevalence of obesity.

Also, the way the researchers categorized their participants is problematic, write the commentators. They combined overweight and obese children on one hand and overweight and normal-weight adults on the other. Thus, an overweight child who became an overweight adult was categorized as "high-BMI resolving." Meanwhile, a normal-weight child who became an overweight adult was categorized as "reference."

Finally, the findings might not apply to the United States because children are heavier on average there, Dr Ogden and colleagues point out.

The study was funded by the Academy of Finland; the Social Insurance Institution of Finland; Competitive State Research Financing of the Expert Responsibility area of Kuopio, Tampere, and Turku University Hospitals; the Juho Vainio Foundation; the Paavo Nurmi Foundation; the Finnish Foundation for Cardiovascular Research; the Finnish Cultural Foundation; the Tampere Tuberculosis Foundation; the Emil Aaltonen Foundation; the Yrjö Jahnsson Foundation; the Signe and Ane Gyllenberg Foundation; the Diabetes Research Foundation of the Finnish Diabetes Association; the Sigrid Juselius Foundation; the Maud Kuistila Foundation; the Finnish Medical Foundation; the Orion-Farmos Research Foundation; and the National Health and Medical Research Council. The authors and the commentators have disclosed no relevant financial relationships.

Pediatrics. Published online December 19, 2017. Article abstract, Commentary extract

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