weight gain among those treated for obesity to prevent progression from a moderate to more severe levels? Does the success of prevention efforts depend upon the effect on comorbid medical disabilities (e.g., diabetes or hypertension)? Is what should be stopped or kept from happening an underlying risk condition or predisposition factor for obesity development?

A recent Institute of Medicine (IOM) report recommends an approach to clarifying definitions of prevention that, although developed in relation to mental disorders, apply to obesity (IOM, 1994). This IOM report reviews existing classification systems for preventive interventions for physical illness. The familiar public health classification system designates three types of prevention: primary, secondary, and tertiary. The goal of primary prevention is to decrease the number of new cases (incidence) of a disorder. In secondary prevention, the goal is to lower the rate of established cases of the disorder in the population (prevalence). Tertiary prevention seeks to stabilize or decrease the amount of disability associated with an existing disorder. For obesity, tertiary prevention could refer to decreasing the progression to more severe obesity or decreasing the likelihood of associated musculoskeletal, metabolic, or vascular disorders (e.g., osteoarthritis, diabetes, or cardiovascular disease).

When this prevention classification system was introduced more than 25 years ago, the implicit disease model was one of an acute condition with a specific and unifactorial cause. It was assumed that mechanisms linking the cause of a specific disease to its subsequent occurrence could be identified. In the intervening years, many chronic diseases prevalent in this country have been recognized as having multifactorial etiologies. Research on these diseases has advanced our knowledge about the complicated relations that exist between risk factors and protective factors for disease and the outcomes of preventive interventions. But this knowledge can breed the pessimistic view that prevention efforts will be futile until the etiologies of diseases are better understood (IOM, 1994).

According to this analysis, the concept of risk reduction is critical to prevention programs and research. Addressing the degrees of risk for a condition supplants the more simplistic concept of prevention in which a disease is simply present or absent. Risk factors refer to those characteristics that, if present for a particular individual, make it more likely that this person (compared to someone selected from the general population) will develop a disorder (Werner and Smith, 1992). Both risk and protective factors are included here. Research also shows that many at-risk individuals have factors in their background or environment that protect against the development of a disorder (Garmezy, 1983).

In furthering the establishment of successful preventive intervention programs, the IOM report recommends instituting a "preventive intervention

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