Method: The review followed PRISMA guidelines to ensure methodological quality and systematic reporting. Inclusion and exclusion criteria were defined to include randomized controlled trials of nutrition intervention programs with an educational and psychosocial component to improve fruit and vegetable (FV) intake in young adults (18-34 years old). There were no restrictions on year of publication. A wide-net search strategy across Medline (PubMed and Ovid), CINAHL, PsychInfo, Embase, and Web of Science was conducted. A search syntax was created by combining a comprehensive list of keywords synonymous to “nutrition interventions” and “young adults.” Each syntax was developed upon consultation with a librarian and narrowed using an iterative approach. Backward and forward searches were also conducted using published systematic reviews on young adult nutrition interventions. Each study was assessed for risk of bias. Data from included studies were extracted and synthesized.
Results: A total of 2,770 records were identified. After full-text review, 21 studies were included. Most studies had high or some risk of bias, primarily due to sampling and measurement bias. Low-income, people of color, not in higher education were underrepresented. Some studies also found unintended outcomes (boomerang effects). Furthermore, a typology of interventions emerged as an organizing framework from the intervention content and method of delivery. Interventions were 1.) anticipatory, 2.) socially-engaged, 3.) exposure-based or a hybrid. Most interventions finding positive changes in FV intake were anticipatory and or socially-engaged. Such programs provided planning tasks and or addressed social norms catering to developmental needs unique to early adulthood, such as adjusting to social expectations and facing new barriers. Intervention arms with minimal or no change in FV intake 1.) lacked planning or goal-setting components, 2.) only provided information or delivered messages on non-interactive platforms, and 3.) had individuals without “healthy” intentions or identities, or differed in progress with other participants.
Conclusions and Implications: Future studies should investigate methodological strategies to address sampling bias, measurement error, and high attrition to reduce bias. Synthesizing unintended outcomes indicates a possible ceiling effect for fruit intake and inadvertent effects of the intervention including avoidance and discouragement. Further research is needed to understand boomerang effects to prevent any harm. Additionally, more studies focusing on low-income young adults of color are imperative as socioeconomic inequalities contribute to dietary disparities. Research also suggests that food behaviors are multigenerational and cultural (Brombach, 2017; Douglas, 2012). Hence, establishing positive dietary behaviors in young adults has implications beyond the individual, to future families and communities.