New study may have parents asking how they can help their children maintain a healthy weight all year long.

The fall semester is well underway and most kids are getting into a routine that includes healthy school lunches and regular physical activity.

That routine could be part of what’s helping them to shed some of the weight that some of them gained during the summer.

A new study says those lazy days of summer are actually when young children put on the pounds.

The research from The University of Texas at Austin was published today in the journal Obesity.

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Paul von Hippel, Ph.D., an associate professor at the university, looked at body mass index (BMI) and obesity prevalence in 18,170 children between the time they began kindergarten in 2010, through the end of second grade in 2013.

During that time, all of the increases in the number of overweight and obese children happened during summer vacations — not during the school year, researchers reported.

Between the start of kindergarten and the end of second grade, the prevalence of obesity went up from almost 9 percent to more than 11 percent. The prevalence of overweight children increased from 23 percent to 28 percent.

During the school year, overweight prevalence did not change, and obesity prevalence went down slightly.

In 2007, von Hippel published a study that found young children gain weight faster during summer vacation than during kindergarten and first grade.

Some children may be more active during the school year or have access to more regulated meals at school. Then during the summer, they can probably access food any time they want and may not be as active, Amy Gorin, a New Jersey-based nutritionist, told Healthline.

Amy Morin, a Maine-based psychotherapist, said children may gain weight during summer because they don’t get enough exercise, and they have more opportunities to snack.

“Children may be more likely to reach for a snack when they walk past the kitchen, and many of them are eating while using their electronics,” Morin told Healthline. “Mindless snacking may prevent them from feeling satisfied.”

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Ensuring healthy eating for the entire year isn’t necessarily an easy goal to accomplish.

“I wish I could say that changes schools have made over the last decade are helping to reduce obesity, but they’re not,” von Hippel said in a statement.

He says the trend of gaining weight over the summer won’t stop if health and school professionals focus only on school food and physical education during the school year. Programs should target children’s behaviors throughout the entire year.

It’s important to encourage children to be active and to limit screen time, Gorin said.

In addition, she added, it is vital to teach children to eat healthy snacks both at home and while at school.

“As the parent, you control the grocery shopping,” she noted.

Parents who are concerned about a child’s weight shouldn’t put the focus on losing weight. Instead, the focus should be on getting healthy, Morin said.

“Make it a family affair to eat healthy and to get exercise together. Creating a healthy lifestyle for everyone will ensure your child doesn’t feel like he’s being singled out or that there’s something wrong with him [or her],” Morin said.

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