WASHINGTON (AFP) - While many Americans struggle with extra weight, the obesity rate among United States (US) pre-schoolers has dropped by nearly half in recent years, according to figures out on Tuesday.

Just 8 per cent of children aged two to five were obese in 2011-2012, down from 14 per cent in 2003-2004, according to findings from the US Centers for Disease Control (CDC) and Prevention, published in the Journal of the American Medical Association.

"We continue to see signs that, for some children in this country, the scales are tipping," said the CDC's Tom Frieden.

He highlighted that the study comes on the heels of previously-released CDC data showing a "significant decline" in obesity among low-income children aged two to four participating in federal nutrition programmes.

"This confirms that, at least for kids, we can turn the tide and begin to reverse the obesity epidemic," he added.

The exact reasons for the drop are unclear. However, many childcare centres have recently started boosting their nutritional and physical activity standards, the CDC said in a statement.

Other possible reasons, it added, could be higher breastfeeding rates and a decline in the consumption of sugary drinks.

First Lady Michelle Obama - whose "Let's Move" campaign is aimed at tackling childhood obesity - welcomed the new numbers.

"I am thrilled at the progress we've made over the last few years in obesity rates among our youngest Americans," she said. "With the participation of kids, parents, and communities in Let's Move! these last four years, healthier habits are beginning to become the new norm."

Overall, however, the prevalence of obesity remains high in the US and, for the first time in two decades, the White House is expected to unveil updated nutrition labelling on Thursday.

The CDC study also found that about a third of adults and 17 per cent of children and teenagers were obese in 2011-2012, representing no significant changes.