Newswise — MAYWOOD, Ill. – In the fight against childhood obesity, summer is one of the most challenging times of the year.

During the school year, many students walk to school, go to gym class, play outside at recess and participate in after-school sports. They are allowed to eat only during designated times, and typically find little or no junk food in modern-day school cafeterias and vending machines.

“In school, you can’t keep snacking while you’re learning history,” said Lara Dugas, PhD, MPH, a physical activity epidemiologist who has studied childhood obesity. Dr. Dugas is an assistant professor in the Department of Public Health Sciences at Loyola University Chicago Stritch School of Medicine.

But during the summer months, many children have relatively little structure or supervision. This is especially true in low-income households that can’t afford summer camps. Consequently, kids get less exercise and may have unlimited access to junk food all day long.

“Many children finish the school year in June fitter and leaner than when they go back to school in August,” Dr. Dugas said.

In the past 30 years, childhood obesity has more than doubled in children and quadrupled in adolescents, according to the U.S. Centers for Disease Control and Prevention. In 2012, more than one-third of children and adolescents were overweight or obese, the CDC said.

To help fight the summer obesity spike, Dr. Dugas recommends getting children involved in summer camps, sports teams and park district activities. “Such structured activities provide opportunities to benefit both their physical and cognitive development,” Dr. Dugas said.

Dr. Dugas also recommends parents try to limit the amount of junk food kids can eat. For example, she said, buy more fruits and vegetables and less salty snacks, and avoid sugar-sweetened beverages. “Water is good enough,” she said.