School gardening projects have a modest positive impact on children’s nutrition and body measurements This systematic literature review and meta-analysis performed by an Italian team examined the impact of school gardening activities on both nutrition and body outcomes. By including body outcomes, such as Body Mass Index (BMI) and waist circumference, the review addressed a gap in the scientific literature. The main goal was to provide clinicians and policy makers with sound scientific evidence regarding the role that school gardening programs might play in preventing or reducing obesity in children.
The review portion of the study used strict protocols to search four databases for relevant studies and include or exclude them based on their study populations, methodologies, and measured outcomes. They restricted this review to studies of school-based gardening programs that served children 6-12 years old and measured nutritional behaviors and/or anthropometric outcomes. Approved study designs included true experiments, quasi-experiments, and observational studies. Next, the Italian research team analyzed the risk of bias for each study, using a protocol to label studies for high, low, or unclear risk for bias. This selection process yielded 33 studies for review and 5 studies for the meta-analysis. For the meta-analysis, the researchers extracted data from 5 studies that reported anthropometric data and ran several statistical tests to compare combined body and obesity measures for groups of children who participated in school garden programs with groups who did not.
The reviewed studies linked school gardening activities to three categories of outcomes: fruit/vegetable consumption and dietary habits, anthropometric measures (i.e. BMI, waist circumference), and other measures (i.e. physical activity, academic performance, blood tests, etc.). For fruit and vegetable related outcomes, several studies reported positive effects on children’s fruit/vegetable intake, fruit/vegetable knowledge, and fruit-vegetable attitudes and behaviors. Only 6 studies included anthropometric outcomes; generally, they reported significant reductions in anthropometric measures as a result of the school gardening activities. One found a significant reduction in BMI for the overweight/obese group only. Another study found no significant BMI reduction at the end of year 1 but did document a significant reduction a year later; this study also found a significant reduction in BMI metrics for children in the low-income subgroup. For other outcomes, some studies linked school gardening activities to increased physical activity, science achievement scores, and math scores (low-income children only). Two studies reported lower blood pressure but no significant effects on health markers from blood and urine samples. Finally, findings from separate meta-analyses (conducted on subgroups of studies based on similarity of their outcome measures) were mixed: a meta-analysis of 2 studies showed non-significant increases in BMI measures; combined statistics from 4 studies showed non-significant decreases in one type of BMI measure but significant decreases in another; another combination of 3 studies showed a significant decrease in waist circumference coupled with statistically insignificant increases in blood pressure.
The authors call for more high-quality studies to draw stronger conclusions about the impact of school gardening activities on children’s body metrics and general health. However, this combined review and meta-analysis generally confirms that school gardening activities are associated with improved fruit and vegetable intake and nutritional knowledge. In addition, some evidence suggests that school programs which combined gardening + nutritional education were more effective than nutritional education only. Other outcomes showed insignificant or inconsistent results. The meta-analysis showed a mix of non-significant relationships and some evidence that some school gardening programs were linked to healthier body measures. Based on these mixed findings and the small number of studies that examined anthropometric outcomes, it’s still not clear if school gardening programs have a strong impact on children’s health. Overall, this study suggests there’s moderate descriptive evidence that school gardening projects improve children’s consumption of healthier foods and may reduce their waist circumference and BMI%.
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