When you think of a 3-year-old, the words "obese" and "overweight" probably do not come to mind.
But this may be the age when many children's problems with weight begin, according to a new study published in the American Journal of Public Health.
The study by Rachel Kimbro and her colleagues at the University of Wisconsin in Madison looked at nearly 2,300 urban low-income families.
They found that 35 percent of the 3-year-olds studied were overweight or obese. In addition, Hispanic children were twice as likely as either black or white children to be overweight or obese, suggesting ethnic differences play a big part in childhood obesity.
"There are very few studies of obesity in children this young," said Gary Foster, director of the obesity research center at Temple University School of Medicine. "This study is very important."
Foster said the study addresses some of the factors that put children at risk for obesity at such a young age.
"We have known for a long time that obesity is disproportionately related to income," he said. "The poorer you are, the more likely that you are obese."
Among the other child obesity risk factors suggested by the study are high birth weight, taking a bottle to bed and whether or not a child's mother is obese.
But researchers were not able to fully explain all of the differences. For example, the differences in childhood obesity rates between racial groups could not be entirely blamed on economic status, overall health or parenting habits, the study said.
Other experts argue that the study results are not new and just confirm previous data.
"The finding that we can identify different prevalence rate of obesity in different ethnic groups is not particularly surprising," said Dr. Darwin Deen, professor of family and social medicine at the Albert Einstein College of Medicine in New York. "It correlates well with other data that have shown the same thing.
"The bigger question is whether 3-year-olds in certain ethnic groups are more likely to remain obese as they get older."
While the idea of overweight and obese 3-year-olds is a concern, experts said a majority of children who are overweight at this age outgrow it.
"The 3 to 5 age group is not predictive of being obese as an adult," said Deen. "It's more the older group such as adolescents [that predicts adult obesity]."
But while parents should not necessarily be alarmed if their child is on the heavy side, they should realize the need to change the way they are feeding their child.
"The bottom line is that you can't become overweight without an energy imbalance," said Foster. "And the easiest way is by an imbalance on the intake side.
"It's much easier to increase intake by 500 calories than it is to increase your activity by that much."
Foster said the study findings suggest parents should pay more attention to both the quantity and the quality of food they feed their kids.
And at the earliest ages, breast-feeding seems to be of utmost importance.
"Breast-feeding is extraordinarily important," Deen said. "It's one of the things that plays an important role in preventing obesity.
"This does not mean that most formula-fed babies will become obese or that formula shouldn't be used, but breast-feeding is sort of tailor-made for the child."