Preschool children receiving government food aid are reaching healthier body mass indexes, a U.S. study found, signaling a steady decline in obesity rates.

The latest data shows obesity rates dropped to about 14% in 2016, the Centers for Disease Control and Prevention reported, down from 16% in 2010.

Health experts welcomed the results published Tuesday in the Journal of the American Medical Association, following an upward trend of obesity in young children between 2000 and 2010. All racial and ethnic groups recorded a statistically significant decline in obesity, the study's authors wrote.

“It gives us more hope that this is a real change,” said Heidi Blanck, who heads obesity prevention at the CDC.

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The results cover children ages 2 through 4 on food vouchers and other services in the federal Women, Infants and Children nutrition program. About 20% of U.S. children that age received benefits in 2016.

Adding more fruits, vegetables and whole grains to the nutrition program may have contributed to the decline, researchers said.

Dr. William Dietz, a former CDC obesity expert, called the change substantial, although too many U.S. children are still overweight, he said. About 15% of children ages 2 to 5 nationwide were obese in 2015-2016, according to the American Academy of Pediatrics, putting them at risk of developing diabetes, high blood pressure and heart disease.

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Heavy children often grow up to become heavy teens and adults, so preventing childhood obesity is a priority, researchers say.

Dietz credited the assistance program's switch from high-fat to low-fat milk and the reduction of juice allowed for the reported obesity decline. That amounted to 9,000 fewer monthly calories per child, he said.

Contributing: Kim Painter, USA TODAY; The Associated Press