Laws restricting the sale of food not a part of a school's lunch and breakfast items for students could help fight childhood obesity, according to a new study published in Pediatrics.

The large national study looked at the effectiveness of junk food laws over time. The regulations, usually known as competitive food laws, limit unhealthy options found in vending machines and al a carte stations found in school cafeterias.

Researchers found that children gained less weight from fifth through eighth grade if they lived in states with strong snack laws.

"Competitive food laws in schools reduce weight gain if they are strong and consistent," study author and post-doctoral research associate Dr. Daniel Taber said.

The study also revealed children who were already obese in fifth grade were more likely to reach a healthy weight by eighth grade in states with the laws.

Researchers analyzed data from 40 states, 11 with strong competitive food laws.

In 2008, 20 percent of children aged 6 to 11 were obese, according to the Centers for Disease Control and Prevention. Childhood obesity has also tripled overall in the past 30 years.