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By altering dietary behaviors, nutrition interventions during adolescence have the potential of affecting children at that time and later in life. The majority of interventions implemented in the teen years have occurred in schools, but other intervention sites have included after-school programs, summer camps, community centers, libraries, and grocery stores. Programs with successful outcomes have tended to be behaviorally based, using theories for the developmental framework; included an environmental component; delivered an adequate number of lessons; and emphasized developmentally appropriate strategies. One planning method that can be used in the development of nutrition interventions is Intervention Mapping. The steps of Intervention Mapping include conducting a needs assessment, developing proximal program objectives, mapping appropriate strategies and methods to address the objectives, planning the program design, planning program adoption and implementation, and evaluation. The use of intervention-pl anning techniques, coordination of nutrition and physical education interventions, using technological advances such as CD-ROMs, incorporation of policy changes into intervention efforts, and dissemination of effective programs are all trends that will influence the future development of effective nutrition programs for adolescents.
Adolescence is one of the greatest periods of change throughout the lifetime (1-3). During this time, body shapes are changing (1,2) and independent and abstract cognitive processes begin (4,5), and the adolescent transitions to the social values and roles of adulthood (5). Although adolescence can be marked with new discoveries and opportunities, it can also produce anxiety and turmoil. Biological and hormonal changes, as well as the complex social issues that adolescents face, often overshadow development of protective health behaviors in nutrition and physical activity- behaviors that are viewed as less important and less relevant compared with high-risk behaviors such as experimentation with alcohol and drugs, risky vehicle use, violence, and early sexual activity (6-10).
Recent surveys have shown that the dietary intakes of adolescents are often inadequate when compared with national guidelines. In particular, adolescents consume excessive amounts of fat (particularly saturated fat), sugar, and salt, and inadequate amounts of fruits and vegetables, whole grains, calcium-containing foods, and iron (11-19). In addition, these dietary patterns are often coupled with inadequate physical activity (20). These energy imbalances are linked to development of chronic diseases, such as obesity, cardiovascular disease, type 2 diabetes, and cancer (21,22). Although these diseases have been thought to occur in middle age, recent research has confirmed that nutrition-related chronic disease is now increasing in the adolescent population. The increases in obesity (23), type 2 diabetes (24), and development of cardiovascular disease in children and adolescents (25,26) indicate that nutrition-related problems are becoming a significant cause of morbidity and mortality in youth, and future medi cal expenditures for children with these premature morbidities will eventually tax the economic base of the United States.
Nutrition interventions, especially those that are behaviorally based, have been effective in producing dietary behavior change among adolescents (27); in addition, these behavioral changes can be maintained over time (28). Dietary behaviors have been found to track in individuals over time (29,30), so intervening in youth is cost effective and can influence the development of chronic disease later in life. Public health interventions in particular have the potential to affect youth, especially when disseminated through channels that reach a majority of adolescents, such as schools. Designing a successful nutrition education program for adolescents requires a systematic approach that combines knowledge of determinants of behavior with efficacious strategies and an evaluation plan.
The objective of this manuscript is to identify nutrition intervention programs for adolescents published between 1994 and 2000, list specific elements that contribute to the effectiveness of these programs, provide general guidelines for development of interventions for this population, and discuss upcoming trends in the development of adolescent nutrition education interventions.
REVIEW OF ADOLESCENT NUTRITION INTERVENTIONS
In a 1995 monograph, Lytle (27) reviewed nutrition interventions directed at the general school-aged population. The review included 43 studies: 17 studies conducted since 1990 and 26 studies conducted before 1990 and described in 2 previously published reviews of nutrition education programs (31,32). Although most reported studies were conducted in school settings, some were conducted in other settings such as grocery stores (n=1), libraries (n=1), summer youth nutrition education camp (n=1), and after-school day care (n=1) (33-36). Based on the review of the 43 studies, Lytle concluded that the following elements contributed to the effectiveness of nutrition interventions for adolescents: a behavioral focus, incorporation of instructional strategies that are based on appropriate theory, adequate dose (ie, amount of education required to stimulate positive behavioral change), peer involvement; self-assessment and feedback, environmental interventions to complement behavioral lessons, and community involvemen t (27).
Since 1994, additional nutrition education programs for adolescents have been reported (Figure 1). These programs target a variety of outcomes and have been shown to influence knowledge, attitudes, and behaviors. For this paper, we reviewed all studies that targeted adolescents aged 11 to 18 years (students enrolled in grades 5 through 12); were population-based and conducted in schools, clinics, or communities; were published between 1994 and 2000; and included a student outcome evaluation. Studies were located through literature searches, review of recent nutrition-related journals, and personal communication with those known to be conducting this type of research. Studies that were clinically oriented (37,38) or that included specific subpopulations--for example, pregnant teenagers (39) or high school wrestlers (40)--were excluded. Although many of the studies examined several components of an intervention program, only nutrition-related measurements were reported in Figure 1. The studies reviewed for this paper were all population-based and used strategies appropriate for this purpose; Sigman-Grant (41) discusses individual nutrition counseling as found in clinical interventions.
Using the above criteria, 17 studies were included in the review (Figure 1). These studies were conducted in a variety of settings, although the majority occurred in a school setting. Specifically, 10 studies were conducted in elementary schools, 3 in middle schools, and 2 in high schools; 2 studies were conducted in a community center. The studies were designed to promote cardiovascular health (42-48), decrease obesity (49-51), increase fruit and vegetable consumption (52,53), prevent eating disorders (54), promote generally healthful eating habits for prevention of chronic disease (55,56), reduce cancer risk (57), or to encourage consumption of low-fat meals at school (58).
The studies varied widely in almost all characteristics, including sample size, study design, theoretical framework, and measured outcomes. For example, the number of participants in the interventions ranged from 23 to 2,213. Outcome measures included a wide range of psychosocial and knowledge factors related to dietary behaviors as well as general or specific dietary behaviors. The range of dietary assessments included 24-hour recalls, food records, and brief or traditional food frequency questionnaires. The more successful studies, however, tended to include similar elements that were mentioned in Lytle's earlier review: a behavioral focus (instead of a knowledge-based focus), the application of an appropriate theoretical framework, a focus on individual behaviors as well as the environment (coordinated school health programs), an appropriate dose, a focus on both dietary and physical activity behaviors, and the use of developmentally appropriate and theoretical strategy. Each is described more fully below.
ATTRIBUTES OF SUCCESSFUL PROGRAMS
Although the Knowledge, Attitudes, Behavior model has been used for many school-based interventions, it has not been shown to be particularly effective for school-aged children (27). The goal of knowledge-based nutrition programs is to enhance the knowledge, skills, and attitudes of the target population regarding broad nutritional issues. As a result, this model has been successful in increasing knowledge among children but has not been particularly effective for changing nutrition-related behaviors. Although Lytle et at (27) found quite a few studies that employed the Knowledge, Attitudes, Behavior model, in our review we found no study that explicitly mentioned using this model.
Compared with knowledge-based programs, interventions that have a behavioral focus tend to be more successful in producing behavior change (27,59-61). The goal of behaviorally focused health promotion programs is to enhance health through reduction of risk factors. Theory-driven interventions emphasize specific, desired behaviors as well as the motivators and behavioral skills necessary to engage in these behaviors. Using this approach, the educational outcomes of nutrition programs include changes in specific behaviors such as increasing fruit and vegetables or reducing the amount of fat in the diet, as well as changes in specific behavioral skills necessary to engage in these behaviors. Behavior-oriented nutrition interventions may be offered as part of a coordinated school health program that targets other behaviors as well (eg, physical activity). In our review, the more successful programs were behaviorally focused and targeted other behaviors in addition to the dietary ones.
The most dominant theory used in the development of programs for adolescents has been Social Cognitive Theory (SCT) (62). Social marketing, although not a behavior theory per se, was also cited by 1 study (55). Two studies used specific planning models (ie, the PRECEDE Model and the "Process of Nutrition Education" Model) to develop the programs (52,56). All studies that were theory-based resulted in significant behavior changes.
SCT provides a reciprocal model in which behavior, personal factors, and environmental influences interact continuously. SCT has been particularly effective for developing nutrition programs for children and adolescents. Because children often are not completely in control of their behavior (eg, if they intend to eat more fruit but fruit is not available, they cannot act on their intention), their environment needs to be taken into account as well. Using SCT, both individual behaviors and the environment are proposed to influence behavior.
Social marketing includes the systematic application of commercial marketing principles and practices to the analysis, planning, execution, and evaluation of programs designed to influence behavior change (63,64). It provides a framework for selecting and segmenting target populations and for promotion services and products. Behavior analysis supplies tools for investigating current behaviors, defining and teaching new behaviors, and motivating change. It is usually applied as part of an overall approach in an interdisciplinary combination along with more traditional health-behavior theories.
Most of the effective interventions reviewed in this paper contained an environmental component, which included changes in the physical environment or specific educational efforts devoted to parents or guardians. Several of the interventions reviewed (45,49,52,53,58) included school foodservice components, in which food selections available to children at school were altered to include more healthful …