U.S. Latino youngsters are more likely to become obese by age 3 than black or white children, for reasons that can not be explained by factors such as income and maternal education, a study said on Monday.

The report from Mathematica Policy Research Inc., of Princeton, New Jersey, was based on a review of 2,452 children born in 75 U.S. hospitals and who had reached the age of 3 from 2001 to 2003.

It found that about 18 percent of all of the children were obese by that age but the rate among Hispanics was more than 25 percent compared to 16 percent of black children and more than 14 percent among whites.

The disparity remained even after researchers accounted for socioeconomic factors such as household income, the mother’s education level and whether the children had regular access to food, according to the study.

The obesity levels were determined by measuring body mass index (BMI) during in-home visits, said the report, published in the current issue of Archives of Pediatric and Adolescent Medicine.

BMI is calculated by dividing weight by the square of height. Children who had figures at the 95th percentile or higher for their age and sex were considered obese.

“This disparity in obesity between Hispanic and non-Hispanic children seems to develop early in life, so future research ... should focus on the period from conception to school entry,” the report concluded.

The prevalence of obesity has doubled in the past 25 years in the United States, according to the U.S. Centers for Disease Control and Prevention. About 60 percent of the U.S. population is overweight or obese, with one in three obese.

In an editorial in the same journal commenting on the study, Elena Fuentes-Afflick, a physician at San Francisco General Hospital, said cultural differences could be a factor.

“For Latino immigrants, who may have experienced hunger as children or witnessed the adverse effects of malnutrition, the ideal image of a healthy baby or child may be an ‘overweight’ image by current body mass standards,” she wrote.

A U.S. government study released in 2004 found among adults the highest level of obesity was among non-Hispanic black women followed by Mexican-American women and non-Hispanic white women, with little difference in obesity levels among men based on race or ethnicity.