energy imbalance that over time results in excess weight gain. As a result, quantifying the results of prevention is difficult because the results are less apparent—no change in weight or health outcomes, as opposed to the weight loss and decrease in risk factors associated with treatment (Kumanyika et al., 2008). It is also difficult to measure or, from the individual’s perspective, to be reassured that people are making the small changes in caloric intake and physical activity that may facilitate the prevention of excess weight gain. For this reason, it is important to emphasize universal prevention strategies intended to foster aggregate behaviors along lines that will decrease the likelihood of chronic excess caloric consumption in relation to expenditure. Such approaches focus primarily on modifying social norms and social structures through changes in policies or the implementation of broad interventions that reduce exposure to obesity-promoting environments in the population at large. The same is true for targeted prevention approaches that direct universal strategies at subpopulations (e.g., children and youth, or ethnic or socioeconomic status groups with higher-than-average obesity prevalence). A focus on specific populations may be needed to ensure that interventions address disparities in social and environmental conditions related to eating or physical activity (e.g., in food availability or affordability or in options for physical activity). Universal prevention may address individuals, although not on a one-to-one basis. Examples are mass education or social marketing strategies to improve individual knowledge and skills related to weight change or to promote favorable responses to changes at the environmental or policy level.
Complementary to concepts of obesity prevention that are based on the population segment targeted, public health strategies may also be characterized as affecting macro versus micro environments: macro environments might be at the national, state, or community level, involving variables that affect individuals indirectly, while micro environments might be school, worksite, clinical, or home environments to which