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.
AuldG.WRomanielloC.HeimendingerJ.HambidgeC.HambidgeM.1999Outcomes from a school-based nutrition education program alternating special resource teachers and classroom teachersJ. School Health69403408
BaranowskiT.DavisM.ResnicowK.BaranowskiJ.DoyleC.LinL.S.SmithM.WangD.T.2000Gimme 5 fruit, juice, and vegetables for fun and health: Outcome evaluationHealth Educ. Behav.2796111
BirchL.L.McPheeL.ShobaB.C.PirokE.SteinbergL.1987What kind of exposure reduces children's food neophobia? Looking vs. tastingAppetite9171178
DavisJ.N.VenturaE.E.CookL.T.GyllenhammerL.E.GattoN.M.2011LA Sprouts: A gardening, nutrition, and cooking intervention for Latino youth improves diet and reduces obesityJ. Amer. Dietetic Assn.11112231230
Delgado-NogueraM.TortS.Martínez-ZapataM.J.BonfillX.2011Primary school interventions to promote fruit and vegetable consumption: A systematic review and meta-analysisPrev. Med.5339
FrenchS.A.StablesG.2003Environmental interventions to promote vegetable and fruit consumption among youth in school settingsPrev. Med.37593610
GortmakerS.L.PetersonK.WiechaJ.SobolA.M.DixitS.FoxM.K.LairdN.1999Reducing obesity via a school-based interdisciplinary intervention among youth: Planet HealthArch. Pediatr. Adolesc. Med.153409418
GrahamH.Zidenberg-CherrS.2005California teachers perceive school gardens as an effective nutritional tool to promote healthful eating habitsJ. Amer. Dietetic Assn.10517971800
GurevitchJ.HedgesL.V.1993Meta-analysis: Combining the results of independent experiments p. 378–398. In: S.M. Scheiner and J. Gurevitch (eds.). Design and analysis of ecological experiments. Chapman Hall New York
HedgesL.V.OlkinI.1985Statistical methods for meta-analysis. Academic Press San Diego CA
HeimS.StangJ.IrelandM.2009A garden pilot project enhances fruit and vegetable consumption among childrenJ. Amer. Dietetic Assn.10912201226
HermannJ.R.ParkerS.P.BrownB.J.SieweY.J.DenneyB.A.WalkerS.J.2006After-school gardening improves children’s reported vegetable intake and physical activityJ. Nutr. Educ. Behav.38201202
KochS.WaliczekT.M.ZajicekJ.M.2006The effect of a summer garden program on the nutritional knowledge, attitudes, and behaviors of childrenHortTechnology16620625
LinebergerS.E.ZajicekJ.M.2000Can a hands-on teaching tool affect student’s attitudes and behaviors regarding fruit and vegetables?HortTechnology10593597
McAleeseJ.D.RankinL.L.2007Garden-based nutrition education affects fruit and vegetable consumption in sixth-grade adolescentsJ. Amer. Dietetic Assn.107662665
MorganP.J.WarrenJ.M.LubansD.R.SaundersK.QuickG.CollinsC.E.2010The impact of nutrition education with and without a school garden on knowledge, vegetable intake and preferences and quality of school life among primary school studentsPublic Health Nutr.1319311940
MorrisJ.L.BriggsM.Zidenberg-CherrS.2002Development and evaluation of a garden-enhanced nutrition education curriculum for elementary school children. J. Child Nutr. Mgt. Issue 2. 22 Mar. 2012. <http://docs.schoolnutrition.org/newsroom/jcnm/02fall/morris/>
O’BrienS.A.ShoemakerC.A.2006An after-school gardening club to promote fruit and vegetable consumption among fourth grade students: The assessment of social cognitive theory constructsHortTechnology162429
OgdenC.CarrollM.2010National Center for Health Statistics. Prevalence of obesity among children and adolescents: United States trends 1963-1965 through 2007-2008. 12 June 2012. <http://www.cdc.gov/nchs/data/hestat/obesity_child_07_08/obesity_child_07_08.htm>
ParmerS.M.Salisbury-GlennonJ.ShannonD.StruemplerB.2009School gardens: An experiential learning approach for a nutrition education program to increase fruit and vegetable knowledge, preference, and consumption among second-grade studentsJ. Nutr. Educ. Behav.41212217
PerryC.L.BishopD.B.TaylorG.MurrayD.M.Warren MaysR.DudovitzB.S.SmythM.StoryM.1998Changing fruit and vegetable consumption among children: The 5-a-Day Power Plus Program in St. Paul, MinnesotaAmer. J. Public Health88603609
PerryC.L.BishopD.B.TaylorG.L.DavisM.StoryM.GrayC.BishopS.C.Warren MaysR.A.LytleL.A.HarnackL.2004A randomized school trial of environmental strategies to encourage fruit and vegetable consumption among childrenHealth Educ. Behav.316576
PollanM.2008Farmer in Chief. New York Times Mag. 7 Dec. 2011. <http://www.nytimes.com/2008/10/12/magazine/12policy-t.html>
PostonS.A.ShoemakerC.A.DzewaltowskiD.A.2005A comparison of a gardening and nutrition program with a standard nutrition program in an out-of-school settingHortTechnology15463467
RatcliffeM.M.MerriganK.A.RogersB.L.GoldbergJ.P.2011The effects of school garden experiences on middle school-aged students’ knowledge, attitudes, and behaviors associated with vegetable consumptionHealth Promot. Pract.123643
ReynoldsK.D.FranklinF.A.BinkleyD.RaczynskiJ.M.HarringtonK.F.KirkK.A.PersonS.2000Increasing the fruit and vegetable consumption of fourth-graders: Results from the High 5 ProjectPrev. Med.30309319
RosenbergM.S.AdamsD.C.GurevitchJ.2000MetaWin: Statistical software for meta-analysis with resampling tests ver. 2.0. Sinauer Assoc. Sunderland MA
Siega-Riz A.M. L.E. Ghormil C. Mobley B. Gillis D. Stadler J. Hartstein S.L. Volpe A. Virus and J. Bridgman and the HEALTHY Study Group. 2011. The effects of the HEALTHY study intervention on middle school student dietary intakes. Intl. J. Behavioral Nutr. Phys. Activity 8:7. 22 Mar. 2012. <http://www.ijbnpa.org/content/8/1/7>
SticeE.ShawH.MartiC.N.2006A meta-analytic review of obesity prevention programs for children and adolescents: The skinny on interventions that workEcol. Bull.132667691
U.S. Department of Agriculture2011Supplemental Nutrition Assistance Program education: SNAP-Ed plan guidance Fiscal Year 2012. 22 Mar. 2012. <www.nal.usda.gov/fsn/Guidance/FY2012SNAP-EdGuidance.pdf>
U.S. Department of Agriculture2012Supplemental Nutrition Assistance Program education: SNAP-Ed plan guidance Fiscal Year 2013. 2 May 2012. <www.nal.usda.gov/fsn/Guidance/FY2013SNAP-EdPlanGuidance.pdf>
WrightW.RowellL.2010Examining the effect of gardening on vegetable consumption among youth in kindergarten through fifth gradeWis. Med. J.109125129