WASHINGTON (Reuters) - U.S. children eat an average three snacks a day on top of three regular meals, a finding that could explain why the childhood obesity rate has risen to more than 16 percent, researchers said on Tuesday.

Pedestrians wait to walk across a street near Times Square in New York August 28, 2007. REUTERS/Lucas Jackson

Children snack so often that they are “moving toward constant eating,” Carmen Piernas and Barry Popkin of the University of North Carolina reported.

More than 27 percent of calories that American kids take in come from snacks, Piernas and Popkin reported in the journal Health Affairs. The researchers defined snacks as food eaten outside regular meals.

The studies will help fuel President Barack Obama’s initiative to fight obesity in childhood, something Obama’s wife, first lady Michelle Obama, notes could drive up already soaring U.S. healthcare costs.

Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, wrote a commentary calling for taxes on sugary drinks and junk food, zoning restrictions on fast-food outlets around schools and bans on advertising unhealthy food to children.

“Government at national, state, and local levels, spearheaded by public health agencies, must take action,” he wrote.

Piernas and Popkin looked at data on 31,337 children aged 2 to 18 from four different federal surveys on food and eating.

“Childhood snacking trends are moving toward three snacks per day, and more than 27 percent of children’s daily calories are coming from snacks. The largest increases have been in salty snacks and candy. Desserts and sweetened beverages remain the major sources of calories from snacks,” they wrote.

“Children increased their caloric intake by 113 calories per day from 1977 to 2006,” they added.

CONSTANT EATING

“This raises the question of whether the physiological basis for eating is becoming deregulated, as our children are moving toward constant eating.”

In a second study in the journal, Christina Bethell of the Oregon Health and Science University in Portland and colleagues analyzed data from the 2007 National Survey of Children’s Health to find the rate of obesity for children 10 to 17 rose from 14.8 percent in 2003 to 16.4 percent in 2007.

The percentage of children who are overweight stayed at around 15 percent, they found.

“While combined overweight and obesity rates appear to be leveling off, our findings suggest a possible increase in the severity of the national childhood obesity epidemic,” Bethell said in a statement.

Parents, educators and policymakers all hold responsibility for this, Michelle Obama told the School Nutrition Association conference in Washington on Monday.

“Our kids didn’t do this to themselves,” Obama said.

“From fast food, to vending machines packed with chips and candy, to a la carte lines, we tempt our kids with all kinds of unhealthy choices every day.”

Other studies have shown that obese children are more likely to stay obese as adults, and they develop chronic conditions at younger ages, burdening the healthcare system.

“You see kids who are at higher risk of conditions like diabetes, and cancer, and heart disease -- conditions that cost billions of dollars a year to treat,” Michelle Obama said.

The administration has launched an initiative to tackle the issue by improving nutritional standards, getting food companies to voluntarily improve nutrition standards, help kids exercise more and educating parents.

The effects extend beyond health. Bethell’s study found that overweight or obese children were 32 percent more likely to have to repeat a grade in school and 59 percent more likely than normal weight kids to have missed more than two weeks of school.