The committee faced a significant challenge in deciding what types of evidence to use in formulating recommendations for obesity prevention in children and youth. A review of randomized controlled interventions for obesity prevention and treatment among children and adolescents identified only 35 such studies (Campbell et al., 2002). Due to the limited number of RCTs in obesity prevention efforts and methodological issues, including small sample sizes and high attrition rates of study participants, there is a paucity of RCT data from which to generalize results to broader populations (NHS Centre for Reviews and Dissemination, 2002).
The committee, therefore, developed guidelines for an integrated use of the available evidence to inform population-based obesity prevention interventions and on which to base its recommendations. This was deemed necessary to enhance the biological, psychosocial, and environmental plausibility of its inferences and identify consistency and congruency of information due to the paucity of causal research. Such an integrated-evidence approach has been used successfully to apply science-based principles to other public health efforts (Appendix D), such as in establishing a framework for evaluating the safety of dietary-supplement ingredients (IOM and NRC, 2004).
As childhood obesity is a serious public health problem calling for immediate reductions in obesity prevalence and in its health and social consequences, the committee strongly believed that actions should be based on the best available evidence—as opposed to waiting for the best possible evidence.
The different types of evidence that the committee used in developing the report’s recommendations are illustrated in Table 3-5, and the following principles guided the committee’s process:
Evidence is needed to inform and guide policy and programmatic decisions, justify a course of action, and evaluate the effectiveness of interventions that support obesity prevention.
Although the strength of the evidence is a basis for policy development, other considerations—including the fiscal and sociopolitical climate within which governments, institutions, and communities operate—must also be taken into account (Tang et al., 2003).
Absence of experimental evidence does not indicate a lack of causation or the ineffectiveness of an obesity prevention intervention. Given the methodological challenges, as well as the complexities in linkages between different elements and in their environments, certain interventions may prove effective even though their mechanisms for success are not known.