Behavioral and dietary lifestyles responsible for weight gain and obesity are often learned at an early age (Cooke, 2007). Children (particularly adolescents) who are overweight are more likely to be overweight or obese during adulthood (Dietz, 1998) and are at risk for a variety of physical and psychosocial complications during their lifetime (Ebbeling et al., 2002). Thus, it is troubling that the prevalence of obesity among children and adolescents in the United States has more than doubled between 1963–65 and 2007–08 (Ogden and Carroll, 2010).
Although genetics are known to influence an individual’s body mass index (BMI), environmental factors are thought to be largely responsible for rising obesity rates (Ebbeling et al., 2002; French and Stables, 2003). Creating environments where children are encouraged to be physically active and to choose nutrient-dense foods (such as fruit and vegetables) is thus often the focus of interventions that aim to promote healthy BMI and reduce the risk of childhood obesity (Stice et al., 2006).
Gardens and other sites of participatory food production are prime sites for such interventions. Gardens, in particular, can be used at a variety of educational sites as “learning laboratories” that may positively influence eating habits and increase physical activity in children. Specifically, children’s willingness to taste vegetables (Morris et al., 2001), knowledge of nutrition (Morris et al., 2002), and preference for fruit and vegetables (Hermann et al., 2006; Lineberger and Zajicek, 2000) have been shown to be positively affected by garden-based educational activities. These results highlight the potential importance of garden-based activities to support a comprehensive nutrition education program.
Recently, there has been resurgent interest in educational gardens, prompted in part by high-profile calls for a garden in every school (Pollan, 2008) to foster an “edible education.” Although educators may support the use of school gardens to promote healthy eating (Graham and Zidenberg-Cherr, 2005), lack of resources impedes the broader integration of gardens into school activities (Graham et al., 2005).
To effectively promote healthy eating habits via the use of school gardens, it is important to develop a thorough understanding of the efficacy of garden-based nutrition education programs. Although a handful of individual studies suggest that garden-based, experiential education activities are effective vehicles for increasing fruit and vegetable consumption and promoting healthy food choices in young children, many studies suffer from low statistical power because of small sample sizes and lack of long-term data (Robinson-O'Brien et al., 2009). In addition, because there is a practical limit to the number of servings of fruit and vegetables a child can consume per day, researchers studying the impact of school gardens on changes in fruit and vegetable consumption must be able to detect behavioral outcomes that are small in magnitude. Detecting such small changes requires a high degree of statistical power, which is often beyond the capability of a single study.
Meta-analysis offers a solution to the dilemma of low statistical power in individual studies by synthesizing the results of multiple independent studies that test the same hypothesis (Gurevitch and Hedges, 1993). Specifically, meta-analysis increases statistical power and reduces type II errors and is thus especially useful for summarizing experiments with low sample sizes and/or weak treatment effects (Arnqvist and Wooster, 1995). An additional benefit of meta-analytical techniques is that they can quantify the magnitude of a treatment effect for individual studies included in the analysis, as well as calculate the overall magnitude and significance of the cumulative effect across all studies examined (Rosenberg et al., 2000).
We used meta-analytical techniques to test the hypotheses that, over time, participation in an educational garden program would increase students’ knowledge of nutrition, increase students’ preference for fruit and vegetables, and increase students’ consumption of fruit and vegetables. Specifically, we tested the hypothesis that garden-based nutrition education programs have greater impact on measured outcomes (e.g., nutrition knowledge, fruit and vegetable preference, fruit and vegetable consumption) than traditional nutrition education programs.
To illustrate the importance of repeated studies and statistical power to answer these questions, we also present the results of a vote counting analysis. Vote counting synthesizes the results of multiple studies by counting the number of nonsignificant and significant outcomes for a particular question (i.e., do garden-based nutrition education programs increase vegetable consumption in children?). Together, these methods allowed us to address the relative efficacy of garden-based vs. more traditional nutrition education programs for changing knowledge, attitudes, and behaviors that support healthy weight management.
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