The critical window for preventing obesity is earlier than you think

We've long known that weight in childhood sets the stage for adult weight, but now researchers have figured out a "critical window" for weight. And that age by which weight is determined comes earlier than you might expect.

A recent study published in the journal Pediatrics found that children who developed obesity in adulthood had higher average BMIs (Body Mass Index) at age six compared to those who did not have obesity in adulthood. The study, which was led by Marie-Jeanne Buscot, a researcher at the University of Tasmania Menzies Institute for Medical Research, emphasizes the importance of working to prevent obesity even before kids reach six years old—well before many parents likely start thinking seriously about kids' BMIs.

While previous studies have suggested that overweight and obese children have an increased risk for adult heart disease and diabetes, even if their BMI normalizes, few have studied the growth patterns of BMI from childhood to adult obesity. It's important stuff, because previous data from researchers at Harvard suggests that, according to the current levels of childhood obesity, more than half of today's kids will be obese by the time they are 35.

Buscot says there is "substantial evidence from many population-based studies that childhood obesity tracks (or persists) into adulthood, and that once obesity is established, it is difficult to reverse." Unfortunately, most existing programs that aim to prevent childhood obesity focus on older kids, despite the fact that more than half of children who are overweight or have obesity developed higher BMIs before they even turned two.

The Pediatrics study also identified a second critical window: the period around puberty. Girls who had elevated BMIs who were able to plateau their weight by age 16, and boys who were able to stop gaining weight by 21, were more likely to avoid obesity. So interventions that target the adolescent population can potentially help forestall obesity and its related problems. 

To evaluate your child's BMI and ensure they're on track for a healthy adult weight, you can refer to the Centers for Disease Control and Prevention's online charts for boys and girls aged two to 20 years. The CDC also has a page to help you use BMI as a screening tool to assess your child's risk for becoming overweight.

Read more:
One way parents can fight childhood obesity
Are bigger babies better?