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Snack food consumption behavior: a systematic review of theory-based intervention strategies for changing eating behavior

Health interventions have been shown to be associated with an increase in effectiveness of changing people’s behaviors. However, interventions to change snack food consumption are perceived as complex intervention strategies. This systematic review aimed to identify interventions targeted at changing snack food eating behaviors and theory used in interventions. A comprehensive search strategy was performed using databases including Medline, Scopus, Web of Science, and Google Scholar. Articles published between 2010-2019, intervention studies were included and coded to determine whether and how theory was used. More than half of eligible studies on snack food consumption behavior (56.6%) used theory in interventions. 30 articles were identified for inclusion (n = 444). The most-often-used theories were Social Cognitive Theory, Theory of Planned Behavior/Theory of Reasoned Action, and Transtheoretical Model. Intervention strategies targeting the individual level included tailored health communication and goal setting. Commonly used strategies at the interpersonal and organizational level include social support programs and ecological models, respectively. Community-based participatory strategy was used at the community level. These strategies most construct from theories providing information that needs to be changed to promote healthy behavior. Application of theories in interventions enhanced the effectiveness to promote nutrition behavior change. Striving to use theory more thoroughly by applying and testing theories would be crucial to recommend.


Introduction
Snack food consumption may be one of the causes of nutritional problems worldwide among pre-school children, students, and adolescence [1]. Nutrition problems can affect appetite, leading to underweight, overweight and obesity [2,3]. It affects long-term health, for example, obesity is a factor of many chronic diseases such as diabetes, high blood pressure, cardiovascular disease. Diets high in calorie can contribute to increased obesity, high-sodium diets can contribute to increased blood pressure. A high-sugar diet has been linked with an increased incidence of type 2 diabetes due to the links between high sugar intake and obesity and people with diabetes are at risk for high blood pressure [4,5].
There are several interventions that have been used in studies that can change people's behavior of unhealthy snack consumption by testing strategies for behavior change at individuals, interpersonal, organization and community level [6,7,8]. Some strategies developed theoretical foundations and combined theories or concepts that affect outcomes. Theories can be used to explain the structural and determinants of behavior and may provide a helpful basis for designing interventions to change behavior [9,10].
Although large studies systematically reviewed the effectiveness of program intervention for dietary modification measures that affect health, little has been performed to review the theory-based health behavior change programs and assessed the extent to which theory is used in empirical research and the approaches.

Purpose
The purpose of this study was to systematically review food consumption behavior studies on strategies use and theoretical foundations, and to describe the contribution of theory-based intervention and methods in modification of snacking behaviors.
The common steps of conducting systematic review included research background, research criteria, inclusion criteria, selection procedures, checklists for process quality, procedures, data extraction strategies and methods, and synthesis of the extracted data.
There were three research questions for this review:  What are all the relevant researches?  Strategy interventions and foundation theories used?  What are the key findings from intervention studies?

Study selection process
Two researchers selected the relevant research that was based on the above strategy. Both researchers independently chose research studies by title and abstract, then selected from the full text. The selection process has been implemented in four steps.

Data extraction
After the selection process, the researchers collected papers from a database using a program called Endnote. The collected paper from each of the selected researches, were divided into 2 parts. Part 1 extracted basic information about the research paper and Part 2 extracted the content to analyze the outcome of the measures from each paper.

Quality assessment
The quality of each study was assessed by two authors independently, using the quality assessment tool for quantitative studies developed by the Effective Public Health Practice Project (EPHPP) as a discrete step within the systematic review process [11].

Statistical analysis
The descriptive analyses were frequency and percentage and synthesis use qualitative approach; whether the effect of paper has the same direction or conflict, find the conclusion between the results and discuss issues of dispute.

Results
As shown in Table 1, 56.6% of eligible studies used at least one theory in interventions. Of these 30 theory-based intervention studies, the Social Cognitive Theory was mentioned in 12 articles (40.0%). The planning models (TPB/TRA) were mentioned in 12 articles (40.0%). The Transtheoretical Model (stages of change) was mentioned in 4 articles (13.3%), and the other theory was mentioned 2 times (6.7%). A same proportion of these studies examined individual and group interventions.  [12]- [23] [24]- [35] [36]- [39] [40]- [41] Level of intervention in the included studies: -Individual interventions -Group interventions (interpersonal/organization/community) 15 15 Of 30 included studies (Table 2), 12 studies (40.0%) examined individual level of intervention, 10 studies (33.3%) addressed organizational change, 5 studies (16.7%) examined interpersonal change and a few addressed community interventions. Intervention strategies targeting the individual level included goal setting and tailoring. These strategies draw on Social Cognitive Theory and the stages of change construct from the Transtheoretical Model. Commonly used strategies at the interpersonal level include social support programs. Underlying theoretical constructs include social support and social networks. Intervention strategies at the organizational level include ecological model, provider reminders and feedback. At community level of intervention, the mentioned theory was Diffusion of Innovation Theory.  Table 3 reports on theory use in sample cases and the effects of using theories for intervention design. Reviews examined which theories were used in health behavior intervention study and whether theory-based strategies are associated with outcomes.  Based on Diffusion of Innovation Theory, a target group was trained as advocates for optimal population diffusion of information.
-A different group of peer leaders was recruited each week; each leader was asked to recruit a partner for lunchtime activities. Across schools, peer leaders and partners participated.
Multilevel school-based interventions may promote healthy adolescent dietary behaviors. Intervention schools showed significant increases in the proportion of students served fruit and lunch and a significant decrease in the proportion of students buying snacks at school. SCT

Discussion
This review study showed that theories used to explain dietary intake related to snack food consumption were the social cognitive and the planned behavior. More than half of the studies in the reviews used theory to inform an intervention study and some of theories were applied. The findings highlight the importance of application of health behavior theories to move the field forward. Several reviews explored the use of theoretical foundation led to desirable outcomes and the effects of using theories as the basis for interventions. The use of theories that fit well with the problems and context in the studies might explain the success of theory-based interventions.
The most-often used theories in the reviewed studies were Social Cognitive Theory (SCT). Other widely mentioned theoretical models and planning frameworks were Theory of Planned Behavior (TPB) and Theory of Reasoned Action (TRA) as well as Social support and Social networks. Most of these studies examined individual and organizational interventions and few addressed interpersonal change, and community interventions. The Ecological Model and Diffusion of Innovation Theory were mentioned as theoretical model that has informed an organization and community intervention. These promising models need to be fully applied in research. The Ecological Model has been considered as an acceptable framework to link individual and social behaviors with environmental determinants, to reduce serious and prevalent health problems [42].
As a theory-based intervention, the dietary intake programme applied all of the constructs of SCT as strategies for behavioral change [43]. The Social Cognitive Theory (SCT) is a widely used theory for nutrition education programming [44]. Social cognitive theory addresses motivation and also practical behavioral capability, including skill development, self-control or volitional choice, self-direction of behavior, and impediments and facilitators of behavior change [45].
The Theory of Planned Behaviour (TPB) is an extension of the Theory of Reasoned Action (TRA). Both models are based on the premise that individuals make logical, reasoned decisions to engage in specific behaviours by evaluating the information available to them. The Theory of Reasoned Action (TRA) used in nutrition interventions guided the GTLW framework. In both GTLW and F2C, activities and messages at school were expected to influence children through changes in attitudes and perceived social norms. The Transtheoretical Model of Behavior Change (TTM) provides a framework for understanding a person's intention to make a healthful behavior change and how he or she acts upon that intention [46]. Applying Diffusion of Innovations theory in school-based intervention to promote healthy dietary behaviors spreads through a community may identify several factors that influence behavior change.
These health behavioral theories are useful to guide and develop intervention strategies. Therefore, studies based on theories are more effective in relation to behavioral changes compared to non-theoretical approaches [47]. There is evidence that theories are influenced by social and psychological determinants and that the approach is based on the self-regulation process and on how different social cognitive aspects are associated with eating behaviors [48]. Thus, application of theory should improve the effectiveness of interventions. However, most of the theories that are applied in behavior nutrition interventions provide information on what needs to be changed to promote healthy behavior but not on how change can be induced. Furthermore, some of these theories lack a strong empirical foundation and do better in explaining behavior intentions or motivation than actual behavior or behavior change.

Conclusion
Reviewed studies on snack food eating behavior have shown intervention strategies that most construct from theories. Most of the theories of behavior change applied in interventions provide information that needs to be changed to promote healthy behavior. Application of theories in interventions enhanced the effectiveness to promote nutrition behavior change. Striving to use theory more thoroughly by applying and testing theories would be crucial to recommend. Health behavior changes programs that address significant public health problems should strive to complement individually-oriented intervention models with strategies and models to develop healthier policies, systems and environments. For more effective interventions, behavior change theory needs to be further developed with stronger research designs and further development of behavior change theory should incorporate environmental change strategies.