Between 1971 and 1997, excessive weight tripled as a percentage of all children and teens in Brazil, from 4.1 percent to 13.9 percent, and almost doubled in the U.S., from 15.4 percent to 25.6 percent, Wang said. It increased by a fifth in China from 6.4 percent to 7.7 percent between 1991 and 1997. In contrast, in Russia, it fell from 15.6 percent to 9 percent between 1992 and 1998 during tremendous economic stress and a large reduction in the energy density of the diet.
Overweight prevalence was considerably higher in older children than in adolescents in Brazil, China and Russia but not in the U.S., he said. Also, during the survey periods, the underweight prevalence decreased in Brazil from 14.8 percent to 8.6 percent, in China from 14.5 percent to 13.1 percent and in the U.S. from 5.1 percent to 3.3 percent. The percentage of poorly nourished Russian children climbed from 6.9 percent to 8.1 percent.
Better economic conditions, except in Russia, appear to have spurred the weight gains, Wang said. Other factors were increasingly secure food supplies with more nutrients and higher energy densities, easier access to transportation, more leisure time and growing physical inactivity.
Previous studies documented the increases in excessive weight among adults, and recently, two comprehensive investigations examined obesity in preschool children from developing countries, he said. None, however, has addressed the issue among older children and adolescents internationally, and that's why researchers did the study.
"People have noted the large increase in child and adolescent obesity in the United States and Europe or tiny samples in a few other countries, but no one has had large representative samples in other parts of the world," Popkin said. "Also, most studies have used outmoded standards that were inconsistent between each survey.