In my previous post, I discussed findings from a new study that concluded that obesity rates in the U.S. in the last ten years have leveled off, particularly for women and possibly for men. While a similar trend seems also to apply to children and adolescents, there is one notable exception: obesity rates among heavy boys ages 6-19 seem to be increasing.

These findings were reported in another study published online this week in the Journal of the American Medical Association. The study measured heights and weights for a sample of 719 infants and toddlers (birth to 2 years of age) and for 3281 children and adolescents (2 through 19 years of age). For infants and toddlers, prevalence of high weight was determined as being more than the 95th percentile of the Centers for Disease Control and Prevention growth charts. For children and adolescents, prevalence of high BMI (Body Mass Index, a measure of body fat based on height and weight) was defined at 3 levels: BMI for age at or above the 97th percentile, at or above the 95th percentile, and at or above the 85th percentile, based on specific growth charts.

The main findings were that, in 2008, “approximately 10% of infants and toddlers younger than 2 years were at or above the 95th percentile of weight-for-recumbent length growth charts. Almost 12% of 2- through 19-year-old children and adolescents were at or above the 97th percentile of the BMI-for-age growth charts while almost 17% were at or above the 95th percentile and almost 32% were at or above the 85th percentile.”

These numbers suggest that the obesity problem for children and adolescents is still significant. However trend analysis show that, with one exception, the problem did not increase between 1999 and 2008. Among all girls and most boys, there was no increase in weight for length or high BMI over the time periods 1999-2000, 2001-2002, 2003-2004, 2005-2006, and 2007-2008. This is probably related to the fact (reported in my previous post) that women seem to be adopting healthier behaviors over the last 10 years. Children’s diets are directly related to their mothers’ choices, as women are generally the ones that buy the food, prepare it and serve it. Moreover, many schools are not serving as much junk foods and high-calorie beverages as they used to, as school districts across the country have replaced vending machines with healthier lunches snacks, and drinks.

The one exception to the rule seems to be for boys (6-19 years old) that are already heavy: a significant increase in BMI for those that are in the high cut-point (BMI > 97%) was observed between 1999 and 2008. The specific behavioral, biological and environmental factors that are responsible for this increase are still not well understood at this point.