New York City school children slimmed down during the past five years, according to research results published Thursday.

The number of obese children has tripled in the past 30 years, alarming to health experts, but the number of schoolchildren defined as obese citywide decreased 5 percent since 2006, according to a survey published Thursday in Morbidity and Mortality Weekly Report.

Researchers defined obesity from the body to mass index ratio that uses both weight and height to calculate a child's proportions. Children within the top 5 percent BMI score got defined as obese.

Despite the decrease in the prevalence of obesity among New York City public school children, prevalence remains high and warrants continued public health interventions, the authors of the Centers for Disease Control and Prevention concluded.

The obesity survey showed discrepancies in terms of race and poverty. The majority of children impacted by obesity were black or Hispanic, according to the analysis. Despite this, most decreases in obese children stemmed from white children. At the high end, the number of white children aged 5 to 6 decreased nearly a quarter; on the other end, only 0.9 percent of black children aged 11 to 14 stopped being classified as obese.

Over a five year period, researchers took approximately two million BMI measurements of 947,765 students from Kindergarten to eighth grade.

Children in low poverty brackets fared better than their poorer classmates, except for black and white students, where the opposite trend occurred.

CDC offers a BMI calculator for parents and children here.