Discussion

This systematic literature review qualitatively investigated the effects of experiential nutrition programmes on primary school-aged children in relation to cognitive and behavioural outcomes. It further identified key characteristics of successful programmes that achieved significant changes in the outcomes of interest and also provided a robust evaluation thereof. Such information is useful to guide future public health interventions in this setting. Characteristics of successful experiential nutrition interventions included: (1) frequent exposure that include multiple experiences, accompanied by relevant and comprehensive classroom nutrition education; (2) incorporation of parental involvement and take-home activities; (3) presentation in a context that was relevant and appropriate; (4) multicomponent interventions that are conducted on school grounds and (3) involvement of external personnel, such as expert educators, teacher training and volunteers. Involvement of food service providers to increase exposure, availability and accessibility of healthy food options was also beneficial, whilst adequate provision of funding and resources for implementation of the programmes is paramount. Successful interventions guided by a behavioural change theory tended to be the most impactful in terms of creating changes in both the school environment and children’s behaviours.

It has been established that experiential learning accompanied with cross-curricula interventions is most beneficial and effective at producing knowledge and behaviour change in young children^{(Reference Dudley, Cotton and Peralta84)}. In relation to the behavioural changes investigated in this review, garden-based learning strategies appeared to be the most influential strategies that related to dietary outcomes, particularly increased vegetable consumption^{(Reference Duncan, Eyre and Bryant42–Reference Ratcliffe, Rogers and Goldberg48)}, which has proven difficult to achieve with other interventions^{(Reference Evans, Cleghorn and Greenwood4,Reference Tak, te Velde and Brug52)} . Gardening, unlike other experiential nutrition learning styles, has been intensively investigated in recent years^{(Reference Schneider, Pharr and Bungum85)}. Food gardens have gained recognition as not only do they teach children about growing their own foods, but evidence also suggests that when children are involved in the process of growing fruits and vegetables, they are more likely to taste and consume them^{(Reference Carlsson, Williams and Hayes-Conroy39,Reference Langellotto86)} . Potential reasons for the success of the garden-based programmes may include: (1) increased accessibility to healthful foods; (2) increased exposure of children to the practice of growing foods, as these interventions are typically more time intense than others and (3) the broad range of experiences offered including planting, gardening and harvesting through to cooking and tasting opportunities. Garden-based interventions have also been shown to increase children’s willingness to try new foods and their ability to cook and prepare foods^{(Reference Block, Staiger and Gold87)}. The studies also significantly improved the ability of children to identify different FV, as well as other nutritional-related knowledge^{(Reference Davis, Martinez and Spruijt-Metz41–Reference Hutchinson, Christian and Evans49)}. Our findings are supportive of the recommendations of the Community Preventive Services Task Force, Centers for Disease Control and Prevention^{(Reference Savoie-Roskos, Wengreen and Durward88)}, that indicate that food garden interventions, in combination with nutrition education, are effective in increasing vegetable intake in youth.

Interestingly, of the cognitive-based outcomes investigated in this review, cooking-based activities tended to have the most significant changes on student self-efficacy through food preparation skills^{(Reference Zahr and Sibeko64,Reference Jarpe-Ratner, Folkens and Sharma66,Reference Caraher, Wu and Lloyd68,Reference Cunningham-Sabo and Lohse69)} as well as improvements in their food knowledge and preferences^{(Reference Bisset, Daniel and Paquette63,Reference Chen, Goto and Wolff65–Reference Liquori, Contento and Castle67,Reference Cunningham-Sabo and Lohse69–Reference Cunningham-Sabo and Lohse71)} . Cooking programmes offer children a unique hands-on experience that can provide lifelong skills^{(Reference Fordyce-Voorham89)}. These benefits are coherent with similar research on culinary interventions in other settings^{(Reference Hasan, Thompson and Almasri90,Reference Prescott, Lohse and Mitchell91)} .

Food provision programmes have been associated with increasing the consumption of healthy foods and generating positive attitudes towards eating breakfast^{(Reference Bartfeld92)}. The studies included in this review found significant improvements in dietary intakes of healthy foods^{(Reference Murphy, Tapper and Lynch53)} including FV^{(Reference Sharma, Markham and Chow50,Reference He, Sangster Bouck and St Onge51,Reference Kastorini, Lykou and Yannakoulia54)} , wholegrains^{(Reference Sharma, Markham and Chow50,Reference Kastorini, Lykou and Yannakoulia54)} , fibre^{(Reference Sharma, Markham and Chow50)} and dairy foods^{(Reference Kastorini, Lykou and Yannakoulia54)}. All nutrition interventions that included tasting of FV increased overall short-term FV intakes, in addition to food knowledge and preferences. However, as with food provision interventions, results were difficult to demonstrate over the longer term because most studies did not include follow-up post-intervention. Studies which incorporated tasting activities impacted food knowledge through increasing students’ ability to correctly identify certain FV. Interestingly, successful studies identified that increased exposure may lead to more significant results, as reported by one study where it took eight to ten encounters before scholars reported that they ‘liked’ the particular food item^{(Reference Lakkakula, Zanovec and Pierce58)}. Food-related attitudes, choice and intake in children are largely driven by taste preferences. A review by Barends et al. ^{(Reference Barends, Weenen and Warren93)} reported that repeated exposure to vegetables in the first 3 years of life increased acceptance of the target vegetable, whereas exposure to variety was found to be particularly effective in increasing acceptance of a new vegetable. Studies included in the current review support this strategy in older children attending primary school.

Nutrition interventions aimed at improving healthy behaviours need to focus on changing the environment and societal norms^{(Reference Dobbs, Sawers and Thompson94)}. When developing nutrition programmes within primary school settings, interventions need to target the multiple facets of the environment. This requires consideration in providing as many experiences as possible in relation to skills development of growing, cooking and tasting foods. Through increasing exposure and accessibility to healthy foods, the more likely it will be to meaningfully impact health knowledge and behaviour. Some successful interventions, particularly food provision and tasting programmes, achieved this through incorporating a cafeteria component and involved food service providers^{(Reference Sharma, Markham and Chow50,Reference Morrill, Madden and Wengreen60–Reference Perry, Bishop and Taylor62,Reference Liquori, Contento and Castle67,Reference Evans, Rutledge and Medina73,Reference Prelip, Thai and Erausquin74)} which assisted in increasing the exposure, availability and accessibility of healthier options.

Another frequently employed strategy used within experiential interventions was the inclusion of parental involvement and education. Parental involvement in school-based programmes can strengthen the home food environment and reiterate the healthy eating messages and habits being demonstrated at school. Involvement of parents, carers and family members has been identified as an important strategy in changing food-related behaviours in primary school-aged children^{(Reference Nixon, Moore and Douthwaite95)}, but there is limited information on how best to engage parents^{(Reference Hingle, O’Connor and Dave96)}. Studies in the current review which incorporated parental involvement included activities such as take-home produce and recipes to cook and share^{(Reference Duncan, Eyre and Bryant42,Reference Kararo, Kathryn and Neil43,Reference Leuven, Annerie and Leuven45,Reference Sharma, Markham and Chow50,Reference Lachausse61,Reference Perry, Bishop and Taylor62,Reference Zahr and Sibeko64–Reference Jarpe-Ratner, Folkens and Sharma66)} , additional homework activities or challenges^{(Reference Gold, Larson and Tucker59)}, parent education sessions^{(Reference Sharma, Markham and Chow50,Reference Perry, Bishop and Taylor62,Reference Liquori, Contento and Castle67,Reference Quinn and Castle70,Reference Prelip, Thai and Erausquin74)} or parental volunteering in programme supervision^{(Reference Murphy, Tapper and Lynch53,Reference Bisset, Daniel and Paquette63,Reference Liquori, Contento and Castle67)} .

A common implementation strategy used by many of the studies included in this review was the use of external educators^{(Reference Davis, Martinez and Spruijt-Metz41,Reference Hutchinson, Christian and Evans49,Reference Murphy, Tapper and Lynch53,Reference Kastorini, Lykou and Yannakoulia54,Reference Gold, Larson and Tucker59,Reference Lachausse61,Reference Bisset, Daniel and Paquette63–Reference Chen, Goto and Wolff65,Reference Liquori, Contento and Castle67–Reference Cunningham-Sabo and Lohse71,Reference Evans, Rutledge and Medina73)} (including nutritionists/dietitians, chefs, horticulturalists and university researchers/students) or in-depth teacher training^{(Reference Kararo, Kathryn and Neil43,Reference Lineberger and Zajicek44,Reference Ratcliffe, Rogers and Goldberg48,Reference Battjes-Fries, Haveman-Nies and Renes55,Reference Day, Strange and McKay56,Reference Liquori, Contento and Castle67,Reference Quinn and Castle70,Reference Prelip, Thai and Erausquin74)} to assist in the effective delivery of the programmes. It has previously been demonstrated that intervention success is dependent upon a number of factors, with high levels of teacher self-efficacy and prior knowledge related to the intervention being among the most important^{(Reference Kien, Grillich and Nussbaumer-Streit97)}. While the use of external educators and experts is important for ensuring information accuracy and student engagement, this may not be feasible due to funding requirements. Similarly, longer-term interventions with a high degree of implementation are more effective at achieving knowledge and behaviour change of schoolchildren, but upscaling of programmes may not be practical^{(Reference Lehto, Määttä and Lehto98)}.

This review did not include programmes that were totally conducted off school grounds, such as farm visits^{(Reference Moss, Smith and Null99,Reference Bevan, Vitale and Wengreen100)} because it was the aim of the review to identify successful programmes that could be run by all primary schools, regardless of proximity to food production sites, or urban/rural location. In the USA, farm visits are a primary mode of experiential school-based nutrition learning provided through the federally funded USDA Farm to School grant programme⁽¹⁰¹⁾. There is high uptake of this programme⁽¹⁰²⁾, with participation rates of 42 % in some school districts and extensive evaluation thereof^{(Reference Yoder, Liebhart and McCarty76,Reference Joshi, Azuma and Feenstra103–Reference Kropp, Abarca-Orozco and Israel107)} . The definition of USDA Farm to School programmes includes garden education, local procurement for school foods and experiential learning activities in agriculture, food, health or nutrition. Our search criteria did identify some programmes that included Harvest of the Month activities and farm visits, but only if they were included as a component of a larger programme, some of which was held on school grounds^{(Reference Hyland, Stacy and Adamson108–Reference Smith and Kalina114)}. Likewise, the review did not include programmes conducted out of school hours, many of which have been evaluated as being effective for behaviour change^{(Reference Cradock, Barrett and Giles115,Reference Annesi, Smith and Walsh116)} .

The US nationwide Coordinated Approach to Child Health (CATCH) programme⁽¹¹⁷⁾, first developed in the late 1980s and funded by the National Heart Lung and Blood Institute, was not included in the current review because it is paired with a physical activity component, and thus did not meet the eligibility criteria. CATCH has been proven to prevent childhood obesity and is supported by 25 years of operation, with 120 academic papers indicating as much as 11 % decrease in overweight and obesity^{(Reference Luepker, Perry and McKinlay118–Reference Hoelscher, Springer and Ranjit122)}. CATCH creates behaviour change by enabling children to identify healthy foods and by increasing the amount of moderate to vigorous physical activity children engage in each day. Today, CATCH serves children in 10 000 schools and communities across the USA, from pre-K to Grade 8, as well as in after-school settings.

The main limitation that needs to be considered in the interpretation of the findings of this review is the generally low quality of the cited studies. The studies varied extensively in quality; with only eleven of the forty-two cited studies analysed in the review receiving a high-quality GRADE rating, all of which were RCT. School-based programmes are often very challenging to randomise, and it is often not ethically appropriate to do so^{(Reference Eccles, Grimshaw and Campbell123)}.

The short study duration of many included programmes is an additional limitation. Battjes-Fries^{(Reference Battjes-Fries, Haveman-Nies and van Dongen124)} suggests that interventions should last at least 1 year in order to result in meaningful behaviour change. The food provision programmes and food tasting studies all had large sample sizes; however, most of the gardening and cooking studies had smaller sample sizes due to the intensive nature of the interventions. The interventions also lacked continued follow-up to evaluate longer-term results.

Another limitation is the variety of different instruments used to measure outcomes, making comparison between the cited studies difficult. Food provision intervention groups were commonly measured using the validated eighteen-item food security scale^{(Reference Gulliford, Nunes and Rocke125)}, while dietary behaviour change was generally assessed using 24-h-recalls or FFQ. Food tasting programmes largely used non-validated research instruments, which were most often designed by those running the intervention, possibly resulting in misclassification or other biases. A lack of studies from low- and middle-income countries limits generalisability to these settings. Lastly, identification of key characterstics of the interventions deemed to be successful was subjective in nature; therefore, observer bias cannot be ruled out.

Despite these limitations, this review highlights the benefits of experiential interventions and provides direction for future programmes. Vegetable intake was found to be the most difficult of dietary behaviours to change but, collectively, the cited articles suggested that experiential hands-on activities such as gardening, cooking sessions and nutrition education combined with increased exposure to tasting vegetables were the most effective strategies.

A number of key recommendations have resulted from the findings of this review:

• Use behavioural change theory to guide interventions, as these are most impactful in terms of creating changes in both the environment and children’s behaviours;

• Link experiential learning opportunities to specific curriculum topics and integrate with classroom-based learning, rather being provided in isolation;

• Include a focus on influencing the home and community food environment as well as providing exposure to experiential learning opportunities during school hours;

• Incorporate family involvement and take-home activities to encourage healthy eating at home and provide role modelling of good nutrition practices;

• Involve food service providers at schools to increase exposure, availability and accessibility of healthy food options;

• When developing a school garden programme, ensure long-term commitment of at least 3 years, to allow sufficient time to impart skills, mentor across multiple growing seasons and to adequately integrate the garden into the culture of the school;

• Ensure adequate resources are available for maintenance of food gardens, including weeding, watering and harvesting, particularly during school holidays;

• Provide repeated opportunities to taste foods to encourage acceptability by children, especially for vegetables;

• Where possible, include cooking-based activities as these are the most effective interventions that impact student self-efficacy, as well as improve their food knowledge and preferences;

• Engage specialist staff, trained in horticulture and cooking to deliver interventions rather than expect classroom teachers to add gardening or food preparation to their skillset.