As children get ready to head back to school, a new study shows that state laws about foods sold at schools may affect kids' weight.

The study, published in Pediatrics, shows that children are less likely to become or remain overweight if they live in states that have laws limiting the availability of unhealthy foods at school.

The study focuses on foods and drinks sold to students at school snack bars and vending machines.

The researchers say the results should have major implications for federal and state lawmakers as they implement policies targeting childhood obesity.

In the study, researchers followed more than 6,300 fifth- and eighth-grade students in 40 states from 2004 to 2007. They analyzed height and weight information on the children to measure how their BMI changed during the study period, and how strict state laws were on foods sold in schools (apart from federally funded meal programs).

The results showed that children in states with strong and consistent laws at the start of the study had smaller increases in BMI as they got older.