WASHINGTON: Far too many kids are fat by preschool, and Hispanic youngsters are most at risk, says new research that is among the first to focus on children growing up in poverty.

The study couldn't explain the disparity: White, black and Hispanic youngsters alike watched a lot of TV, and researchers spotted no other huge differences between the families.

But one important predictor of a pudgy preschooler was whether the child was still using a bottle at the stunning age of 3, concluded the study being published online on Thursday by the American Journal of Public Health.

"These children are already disadvantaged because their families are poor, and by age 3 they are on track for a lifetime of health problems related to obesity," said lead researcher Rachel Kimbro of the University of Wisconsin, Madison.

Some 17% of US youngsters are obese, and millions more are overweight. Obesity can lead to diabetes, high blood pressure and cholesterol, sleep problems and other disorders — and the problem starts early.

Overweight preschoolers have a five times higher risk of being fat at age 12 than do lean preschoolers, scientists reported last fall.

Kimbro focused on the poor, culling data on more than 2,000 3-year-olds from a study that tracks from birth children born to low-income families in 20 large US cities.

Thirty-two per cent of the white and black tots were either overweight or obese, vs 44% of the Hispanics.

Children were particularly at risk if their mothers were obese. So were those who still took a bottle to bed at age 3, as did 14% of the Hispanic youngsters, 6%of the whites and 4% of the blacks. It supports other research that one of the most common causes of overweight in children is overfeeding.