does not apply to many of the decisions that must be made to prevent obesity. The current research literature lacks the power to set a clear direction for obesity prevention interventions across a range of target populations. Thus, although the concept of evidence-based obesity prevention is likely to resonate with many health professionals, policy makers, and stakeholders, challenges are associated with the identification of data that can be used to address the different types of questions decision makers might need to answer. A range of evidence-based intervention approaches have been developed for such public health issues as tobacco control and immunization. However, there is often a mismatch between the types of evidence that are available to answer public health questions and the types of evidence being generated and published.

With respect to obesity prevention, research into the causal factors driving dietary or energy intake and physical activity levels includes a broad range of designs and evidence, including randomized controlled (experimental) trials and quasi-experimental studies at the individual, organizational, and community levels. Although a similarly broad array of research approaches is potentially applicable to environmental and policy strategies to reduce obesity risk through improved diet and reduced caloric intake and/or increased physical activity, the basic methodologies require different conceptualizations, implementation, and emphases for obesity prevention research—particularly to inform interventions designed to change policies or environmental contexts for eating and physical activity. Although the literature reports some positive findings with respect to strategies that work for obesity prevention, there are many gaps in the evidence. This chapter describes those gaps and reviews concepts from evidence-based public health and public policy that can provide the fundamentals for the use of evidence to address complex population health problems such as obesity prevention. The focus is on the evidence needs most likely to impede progress in obesity prevention and those considered most important to address in the development of an evidence framework to inform decisions about obesity prevention interventions.

STATUS OF THE EVIDENCE BASE

The contrast between the high prevalence and consequent importance of addressing obesity and the paucity of the knowledge base with which to inform prevention efforts is striking. This evidence gap creates tension between the sense of urgency to take action and the lack of specificity about what actions to undertake. This is especially true in circumstances when decision makers cannot wait for a body of literature to be created and critically reviewed.

The evidence for obesity prevention is ideally accumulated from a variety of sources to provide insight into a particular topic, often combining quantitative and qualitative data. To this end, systematic reviews of the intervention literature are undertaken that apply strategies designed to limit bias in the assembly, critical appraisal, and synthesis of all relevant studies on a specific topic (Cook et al., 1995). As noted in Chapter 1, the challenges in evaluating and assembling evidence related



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