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International recommendations advise increasing intakes of fruit and vegetables to help reduce the burden of chronic diseases worldwide. This project systematically reviewed evidence on the effectiveness of interventions and programs promoting fruit and/or vegetable intake in adults. In April 2004, we contacted experts in the field and searched 14 publication databases. We considered all papers published in English, French, Spanish, Portuguese, Russian, Danish, Norwegian, and Swedish, and reporting on interventions and promotion programs encouraging higher intakes of fruit and/or vegetables in free-living not acutely ill adults, with follow-up periods > or = 3 mo, that measured change in intake and had a control group. Forty-four studies (mainly from developed countries) were included in the review and stratified by study setting. Larger effects were generally observed in individuals with preexisting health disorders. In primary prevention interventions in healthy adults, fruit and vegetable intake was increased by approximately 0.1-1.4 serving/d. Consistent positive effects were seen in studies involving face-to-face education or counseling, but interventions using telephone contacts or computer-tailored information appeared to be a reasonable alternative. Community-based multicomponent interventions also had positive findings. This literature review suggests that small increases in fruit and vegetable intake are possible in population subgroups, and that these can be achieved by a variety of approaches. More research is required to examine the effectiveness of specific components of interventions in different populations, particularly less developed countries. There is also a need for a better assessment of the effectiveness and cost-effectiveness of large community-based interventions.

There is growing interest in the potential for complex systems perspectives in evaluation. This reflects a move away from interest in linear chains of cause-and-effect, towards considering health as an outcome of interlinked elements within a connected whole. Although systems-based approaches have a long history, their concrete implications for health decisions are still being assessed. Similarly, the implications of systems perspectives for the conduct of systematic reviews require further consideration. Such reviews underpin decisions about the implementation of effective interventions, and are a crucial part of the development of guidelines. Although they are tried and tested as a means of synthesising evidence on the effectiveness of interventions, their applicability to the synthesis of evidence about complex interventions and complex systems requires further investigation. This paper, one of a series of papers commissioned by the WHO, sets out the concrete methodological implications of a complexity perspective for the conduct of systematic reviews. It focuses on how review questions can be framed within a complexity perspective, and on the implications for the evidence that is reviewed. It proposes criteria which can be used to determine whether or not a complexity perspective will add value to a review or an evidence-based guideline, and describes how to operationalise key aspects of complexity as concrete research questions. Finally, it shows how these questions map onto specific types of evidence, with a focus on the role of qualitative and quantitative evidence, and other types of information.