Competitive foods and beverages include those sold in vending machines that are not a part of reimbursable meals for students.
The improvements observed in the study, published in JAMA Pediatrics, were more noticeable among students whose schools were situated in socioeconomically advantaged neighborhoods, however.
Policies to regulate competitive food and beverages have been adopted by many school districts in response to high rates of childhood obesity in the US. According to the Centers for Disease Control and Prevention (CDC), childhood obesity has more than doubled in children and quadrupled in adolescents over the past 30 years.
The policies adopted by California are identified by the authors of the study as being some of the most comprehensive in the US and have led to significant changes in the food available to students in public schools. California's Department of Education defines competitive foods and beverages as the following:
"Competitive foods and beverages are those that are sold at school outside of and in competition with the federally reimbursable meal programs. Examples of competitive foods and beverages include those sold during the school day in vending machines (that are not reimbursable meals), student stores, á la carte items sold by the school food service department, or as fundraisers."
According to the study authors, the influence of competitive food and beverage policies on the prevalence of student overweight and obesity has not been fully researched. In particular, no study has yet been conducted to investigate potential disparities in the influence of these policies in neighborhoods with differing socioeconomic resources.
For the study, Emma V. Sanchez-Vaznaugh of San Francisco State University and coauthors decided to compare trends in the prevalence of student overweight and obesity before and after the implementation of competitive food and beverage policies in California public elementary schools.
The data analyzed by the researchers covered 2,700,880 fifth-grade students studying at 5,362 public schools between 2001-10. In particular, the researchers investigated whether rates of overweight and obesity differed by education levels and school neighborhood income.
Prevalence of overweight and obesity was found to increase steadily among fifth-grade students in the years preceding the introduction of competitive food and beverage policies, rising from 43.5% in 2001 to 46.6% in 2005.
From 2006 to 2010, the prevalence of overweight and obesity then stabilized, remaining between 46.2% and 45.8% for the remaining years of the study.
'Interventions must address relevant contextual factors' in school neighborhoods
Throughout the study period, overweight and obesity were most prevalent among students whose schools were situated in the least socioeconomically advantaged neighborhoods, and least prevalent among students attending schools in the most socioeconomically advantaged neighborhoods.
Specifically, the researchers found that in 2010, the prevalence of overweight and obesity in the lowest-income neighborhood was 52.8%. In comparison, in the same year the prevalence of overweight and obesity in the highest-income neighborhood was 36.2%.
While the levels of overweight and obesity leveled off among students attending schools in the least socioeconomically advantaged neighborhoods following the introduction of the policies, prevalence was found to decline among those attending schools in the neighborhoods that were home to the highest levels of income and education.
"These findings suggest that [competitive food and beverage] policies may be crucial interventions to prevent child obesity, but the degree of their effectiveness is also likely to depend on influences of socioeconomic resources and other contextual factors within school neighborhoods," the authors state.
Although the study identifies a disparity in the influence of competitive food and beverage policies on students from different socioeconomic areas, it is unable to measure precisely what the cause of this disparity is and whether it lies in the schools or elsewhere.
The authors believe that this gap should be addressed. "To reduce disparities and prevent childhood obesity among all children, school policies and environmental interventions must address relevant contextual factors in neighborhoods surrounding schools," they conclude.
Recently, Medical News Today ran a Spotlight feature investigating how race and ethnicity influence childhood obesity.