Miami (AFP) - More than 57 percent of children in the United States will be obese by age 35 if current trends in weight gain and poor eating habits continue, researchers warned Wednesday.

The risk of obesity is high even among children whose present weight is normal, said the report in the New England Journal of Medicine.

"Only those children with a current healthy weight have less than a 50 percent chance of becoming obese by the age of 35 years," said the study, led by researchers at Harvard University.

Some 36.5 percent of the US adult population is now considered obese, a condition federal health officials define as having a body mass index of 30 or higher.

The annual medical costs of obesity in the United States are more than $147 billion per year, according to the US Centers for Disease Control and Prevention.

"Adult obesity is linked with increased risk of diseases such as diabetes, heart disease, and cancer," said lead author Zachary Ward, an analyst at Harvard University's T.H. Chan School of Public Health.

"Our findings highlight the importance of prevention efforts for all children as they grow up, and of providing early interventions for children with obesity to minimize their risk of serious illness in the future."

The study was based on a simulation model that predicted future trends based on height and weight data from five nationally representative studies of more than 41,000 children and adults.

"Obesity will be a significant problem for most children in the US as they grow older," it said.

"Of the children predicted to have obesity as adults, half will develop it as children."

Weight gain in a child's early years is particularly hard to reverse in adulthood.

Researchers found that among obese toddlers aged two, three out of four will also be obese as adults.

Children with severe obesity -- which affects 4.5 million children in the United States -- face only a one in five chance of being normal weight adults.

Racial and ethnic disparities in weight are already apparent by age two, with black and Hispanics more likely to have obesity than whites -- yet another trend that persists into adulthood.

"It is critically important to implement policies and programs to prevent excess weight gain, starting at an early age," said senior author Steven Gortmaker, professor of the practice of health sociology at Harvard.

"Plenty of cost-effective strategies have been identified that promote healthy foods, beverages, and physical activity within school and community settings."