Improving Obesogenic Dietary Behaviors among Adolescents: A Systematic Review of Randomized Controlled Trials

The overweight and obesity epidemic persists, and over 340 million children and adolescents aged 5–19 were classified as overweight or obese worldwide in 2020. Obesity intervention becomes crucial during the adolescent years due to the increased autonomy and adolescent motivation to oversee one’s own behaviors and lifestyle-related decisions. The objective of the current study was to conduct a systematic review of randomized controlled trials aimed at improving dietary intake and behaviors among adolescents. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were utilized. The key terms used in the searches referred to the study population and the topic of interest and included words and phrases such as “obesity or overweight and adolescents”, “dietary behaviors and adolescents”, “dietary intake and adolescents”, and “dietary habits and adolescents.” A tertiary screening process was employed, and the National Heart, Lung, and Blood Institute Quality Assessment of Controlled Intervention Studies quality scoring tool was utilized to assess the quality of research articles independently by n = 2 researchers. A total of 7441 articles were identified through the database search, and 36 were included in the current systematic review. The most common outcomes explored included dietary behaviors, anthropometric or biometric outcomes, and physical activity. Approximately half of the studies demonstrated significant improvements in the primary outcomes investigated. The majority of the high-impact studies where significant improvements in primary outcomes were demonstrated were conducted in school settings or were multicomponent or multilevel in nature. Thus, interventions targeting dietary behaviors in adolescents that are delivered in the school setting and are multicomponent or multilevel in nature are the most effective in terms of impact on dietary intake, anthropometric or biometric outcomes, and physical activity.


Introduction
Overweight and obesity continue to plague the globe, with rates having tripled since 1975 [1]. In 2020, the World Health Organization reported that 39 million children under the age of 5 and 340 million children and adolescents aged 5-19 were classified as overweight or obese [1]. While developed countries have the highest prevalence rates of childhood obesity, it is important to acknowledge obesity trends in developing countries, as the pervasiveness of childhood and adult obesity alike is increasing, creating a dual burden of malnutrition. While overweight and obesity are often primarily driven by obesogenic behaviors such as dietary overconsumption and physical inactivity, these behaviors are typically a result of socioeconomic and environmental circumstances that create unfavorable conditions to support healthy behaviors.

Data Extraction
The National Heart, Lung, and Blood Institute (NHLBI) Quality Assessment of Controlled Intervention Studies quality scoring tool was utilized to assess the quality of research articles [8]. Two independent researchers assessed the quality of each article. The Controlled Intervention Studies scoring tool is a 14-item, yes-or-no instrument. Through the provision of affirmative (Yes) or negative (No) responses to each item, scorers rate the quality of the article as 'poor', 'fair', or 'good.' In situations where scoring discrepancies occurred, the senior researcher (LH) discussed the article's score with the two independent researchers and came to a consensus regarding inclusion or exclusion. Articles that received a rating of 'good' were included in the current systematic review. Data were extracted and organized in tabular format (see Table 1).
As stated above, eight studies demonstrated significant impacts on dietary behaviors, specifically fruit and vegetable intake, diet quality, and snacking habits. Bogart et al. [18] implemented a school-based obesity-prevention intervention combining school-wide environmental changes, multimedia encouragement to eat healthy school cafeteria foods, and peer-led education. As a result, the intervention group showed significant increases in the proportion of students consuming fruit and lunch and a significant decrease in the proportion of students buying snacks at school. Bessems et al. [41] implemented an eight-lesson educational intervention and observed significantly improved short-and longterm changes in fruit consumption among the intervention participants compared to the control participants. While no intervention effect was observed for BMI, Cunha et al. [37] observed significant improvements in fruit consumption, as well as significant reductions in sugar-sweetened beverage and cookie consumption. Hidayanty et al. [27] observed decreased unfavorable snacking habits in the experimental group of overweight adolescents. Horton et al. [22] and Arredondo et al. [23] explored the impact of a 'promatora'-delivered family-meals intervention in the home. Intervention group participants demonstrated a reduced weekly consumption of fast food, as well as a greater variety of consumed vegetables at 10 months post-intervention. The study of Keshani et al. [26] aimed to assess the impact of educational intervention, based on the health belief model (HBM) and collaborative learning techniques, on diet quality in adolescents, and diet quality improved in the experimental group compared to the control group. Shomaker et al. [5] observed lower food reward and a reduction in stress eating among intervention participants compared to control participants. The study by Ochoa-Avilés [38] aimed at improving the dietary intake and physical activity of Ecuadorian adolescents. As a result, participants from the intervention group consumed lower quantities of unhealthy snacks and less added sugar at the end of the trial. Daily fruit and vegetable intake decreased in both the intervention and control groups compared to baseline.
Several studies have demonstrated the effects of interventions through the observation of significant improvements in anthropometric outcomes. While significant between-group differences were not observed, Bagherniya et al. [29] found significant mean BMI and waist circumference reductions in the intervention group. Bogart et al. [17,18] demonstrated significant reductions in BMI over time among all participants, with significant intervention effects observed for students who were obese at baseline. Ochoa-Avilés et al. [38] observed a reduction in waist circumference in the intervention group at the end of the program. The study by Daly et al. [12] examined the effects of a satiety-focused mindful eating intervention (MEI) on BMI, weight, and mindful awareness, and observed a decrease in BMI in MEI participants compared to the control group participants. Hidayanty et al. [27] aimed to employ social cognitive theory to reduce snacking habits and sedentary activity among overweight adolescents and observed a higher reduction in BMI z-scores and waist circumference among intervention participants.
In their HBM intervention, Keshani et al. [26] observed improvements in not only diet quality but also all HBM factors and knowledge in the experimental group compared to the control group. Bagherniya et al. [29] observed that intervention participants had significantly improved self-efficacy, social support, intention, and situation compared to control participants. In their 'promatora' intervention, Arrendando et al. [23] observed that parent-reported behavioral strategies mediated the effects of the intervention on child dietary outcomes.
Significant improvements in the respective measures of BMI were observed by Anderson et al. [33], Barnes et al. [34], DeBar et al. [24], Friera et al. [43], Vidmar et al. [10], and Viggiano et al. [39]. Additional anthropometric and biometric measures were explored across the studies. Barnes et al. [34], Friera et al. [43], and Viggiano et al. [39] additionally observed significant improvements in waist circumference. Friera et al. [43] additionally observed significant decreases in percent fat mass and systolic and diastolic blood pressure and increases in percent muscle mass at both 3 and 6 months. Contrary to the expected outcomes, Sgambto et al. [36] observed significant increases in BMI among the intervention participants compared to the control participants. Additionally, participants who received both in-school and at-home intervention components showed significantly increased percent body fat compared to the control participants. However, male intervention participants demonstrated a significantly greater decrease in percent body fat.
A multitude of dietary outcomes were assessed across the included research studies, and significant findings were observed in eight of the studies [13,14,19,20,32,34,35,39]. Collins et al. [32] observed greater water intake and a greater proportion of female intervention participants consuming less than one sugar-sweetened beverage at 12 months. Cullen et al. [19] observed a significant increase in vegetable intake among intervention participants. Pberts et al. [13,14] observed significant dietary outcomes at 2, 6, and 8 months. At 2 months, compared to control participants, intervention participants ate breakfast on significantly more days per week, had a lower intake of total sugar, and had a lower intake of added sugar [13]. At 6 months, compared to control participants, intervention participants were more likely to drink soda less than or equal to once per day and eat at a fast-food restaurant less than or equal to once per week [13]. Finally, at 8 months, intervention participants reported eating breakfast on more days per week [14]. Sutherland et al. observed that intervention participants' mean lunchbox energy from recommended foods increased significantly. Viggiano et al. [39] observed significant dietary improvements with regard to the Adolescent Food Habit Checklist at 6 months and 18 months, as well as improved nutrition knowledge and healthy and unhealthy diet food habits as recorded by the dietary questionnaire utilized. Whittemore et al. [20] observed significant improvements in self-efficacy, healthy eating behavior, fruit and vegetable intake, sugar-sweetened drink intake, and junk-food intake among participants.
Similar to dietary outcomes, a variety of outcomes related to physical activity were measured across the studies. Significant improvements were observed for screen time, resistance-training skill competency, self-reported physical activity, and moderate and vigorous exercise. However, Cullen et al. [19] noted that the control participants reported greater physical activity enjoyment. Intervention participants showed significant positive short-and long-term changes in fruit consumption (p = 0.048 and p = 0.033) compared to control participants. Compared to control schools, intervention schools served more fruit (p = 0.006), more lunches (p < 0.001), and fewer snacks (p < 0.001). Compared to control-school students, intervention-school students reported more positive attitudes towards cafeteria food (p = 0.02) and tap water (p = 0.03), greater obesity-prevention knowledge (p = 0.006), increased intentions to drink water from the tap (p = 0.04) or a refillable bottle (p = 0.02), and greater tap-water consumption (p = 0.04).

Bogart 2016 [17]
Two-year follow-up of Bogart 2014 Baseline survey and anthropometric data and 2-year follow-up anthropometric data (n = 1368) Intervention (n = 829) Control (n = 539) Students overall, overweight students, and obese students across groups demonstrated significant decreases in BMI overtime; no significant intervention effect was observed for intervention vs. control students overall. Among students who were obese, a significant intervention effect for improved BMI was observed (p = 0.005).

BMI Percent body fat
Intervention effects on BMI were not observed (p = 0.75). Intervention participants demonstrated significant reductions in sugar-sweetened beverage (p = 0.02) and cookie (p < 0.001) consumption and a significant increase in fruit consumption (p = 0.04).

BMI
At 1 year, there were significant between-group differences for changes in BMI (p = 0.045). Change in mean BMI at 2 years did not differ significantly between the two groups (p = 0.46). Changes in diet quality (Diet Quality Index International (DQI-I) and high-calorie, low-nutrient (HCLN)) Changes in BMI z-score (age and sex standardized body mass index) Intake of macronutrients (energy, carbohydrates, fat, and protein) Self-efficacy DQI-I score also increased with respect to sodium (p < 0.001). NG self-efficacy increased (p < 0.01). At 24 weeks, BMI z-scores decreased in the NG (p < 0.05); no between-group difference was found. Compared to control participants, intervention participants consumed lower quantities of unhealthy snacks (p = 0.04) and less added sugar (p = 0.006) at the end of the intervention. Compared to control participants, intervention participant waist circumference was lower at the end of the intervention (p = 0.005). In three of the four warning-label groups, participants chose sweetened beverages significantly less frequently than in the no-label group. Participants in the nutrition group had healthier BMIs (p = 0.02), while those in the physical activity group reported a lower waist circumference (p = 0.03). Neither the nutrition or physical activity intervention had a significant effect on child BMI scores or child quality of life. No significant synergistic effects were observed for the two interventions combined. NEAT girls' physical activity and nutrition handbook: 10 weeks of health information and home challenges designed to promote healthy eating and physical activity.
Dietary intake was assessed using the Australian Child and Adolescent Eating Survey (ACAES) FFQ There were no statistically significant grouped-by-time effects for dietary intake or food-related behaviors. 12-month trends suggested more intervention group girls had improved water intake (p = 0.052) and consumed < one sweetened beverage per day (p = 0.057). Intervention and control groups both received: (i) Three 30 min lifestyle counseling sessions, 3 months apart; (ii) Individualized nutrition counseling; (iii) Physical activity exercise plan. Intervention (motivational interviewing group (MIG)) focus was collaboration, evocation, and autonomy. Control (conventional intervention group (CIG)) received conventional counseling style with provision of information, instruction, and advice.
BMI z-score Waist circumference Percent of fat mass Percent muscle mass Blood pressure MIG participants demonstrated significant decreases in BMI z-score at both 3 and 6 months (p < 0.001); CIG participant BMI z-scores decreased non-significantly. MIG participants demonstrated a significant decrease in waist circumference, percent fat mass, and systolic and diastolic blood pressure and an increase in percent muscle mass at both 3 and 6 months (ps < 0.01); CIG participants demonstrated a significant increase in abdominal waist circumference, percent fat mass, and systolic and diastolic blood pressure and a decrease in percent muscle mass at both 3 and 6 months (ps < 0.001).  Intervention effects on screentime (p = 0.03), resistance-training skill competency (p < 0.01), and motivational regulations (intrinsic regulation (p = 0.03); identified regulation (p = 0.028); introjected regulation (p = 0.06)) for school sport were observed. Compared to control participants, intervention participants ate breakfast on significantly more days/week, had a lower intake of total sugar, and had a lower intake of added sugar at 2 months. Compared to control participants, intervention participants were more likely to drink soda ≤ one time/day and eat at fast-food restaurants ≤ one time/week at 6 months. No significant differences between groups were observed for BMI, physical activity, or caloric intake.

Discussion
Overweight and obesity persist as medical and public health issues of concern across the globe [1]. Of particular concern are the high rates of overweight and obesity among children and adolescents, due to their detrimental impacts on physical, mental, and social health; academic success; and overall health and wellness. The adolescent developmental period is a particularly unique time for intervention, given the budding autonomy experienced at these ages. The objective of the current study was to systematically review the current peer-reviewed scientific literature to understand what approaches are effective at impacting adolescent obesogenic dietary behaviors, as tested through rigorous RCT designs.
The setting of the interventions varied across the studies included in the current systematic review-school, home, clinical, or online. Of the studies wherein significant improvements were observed for dietary, anthropometric/biometric, or physical activity outcomes, twenty-one included a school intervention setting [12][13][14]17,18,20,[25][26][27][28][29]31,32,34,35,[37][38][39][41][42][43]. Moreover, all but one [24] of the studies that demonstrated significant improvements in more than one category of outcomes (i.e., dietary, anthropometric/biometric, or physical activity outcomes) were conducted in the school setting [13,14,20,27,29,34,35,38,39]. It is known that schools are an opportune setting for interventions with school-aged children, due to the captive-audience nature of the setting as well as the amount of time spent in the setting. Schools can provide access to healthy foods and snacks, spaces for safe and structured play, education, role-modeling, and peer support [47]. With regards to food and snack options, schools often provide meals and snacks as components of national child meal programs, which have nutritional standards (e.g., the United States Department of Agriculture National School Lunch Program). Schooldays also provide structure and routine, as posited by the Structured Days Hypothesis [48], which counter negative obesogenic behaviors. Schools may be a particularly advantageous setting for interventions targeted toward adolescents, given the growing impact of peer influence at this development stage.
Leading professional, governmental, and international organizations have repeatedly recommended approaches to childhood overweight and obesity prevention that include multiple components, social and environmental levels, and systems approaches [49][50][51]. More than half of the high-impact studies were either multicomponent (addressing more than one behavior (e.g., diet and physical activity) or health outcome (e.g., stress and wellbeing)) or multilevel (intervening at more than one level of the socio-ecological model) in nature [13,14,17,18,20,[22][23][24]27,29,31,34,35,38,39]. All of the studies that demonstrated significant improvements in more than one category of outcomes (i.e., dietary, anthropometric/biometric, or physical activity outcomes) were either multicomponent or multilevel in nature [20,24,27,29,38,39]. Despite the recommendations and apparent successes evidenced by this review, the implementation of multicomponent and multilevel interventions remains challenging with regard to resources, capacity, and sustainability.
The present study has some limitations. First, as with any review of scientific literature, publication bias, the selective representation of the findings based on the research hypothesis, could have impacted the summary of the literature and the conclusions drawn across the studies included in the current systematic review. Specifically, the published literature may have been biased towards studies where only significant findings were demonstrated. The authors were limited to rigorously evaluating only studies that had been published in peer-reviewed research journals. Second, given the broad scope of the studies included, i.e., not restricted to a particular country, income group, setting, or type of intervention activity, there was great heterogeneity across the included studies, which may have limited our conclusions. Finally, process outcomes and exposure time were rarely and inconsistently reported, which posed a challenge for comparison across studies.

Conclusions
Adolescence is a unique developmental period, in that the potential for health risks is high, but the emergence of autonomy and peer influence provides a unique opportunity to intervene to curb these health risks. Interventions targeting dietary behaviors in adolescents that are delivered in the school setting and are multicomponent or multilevel in nature are the most effective in terms of impact on dietary intake, anthropometric or biometric outcomes, and physical activity. Professionals in the field should continue to engage in the school setting despite the challenges that exist, e.g., additional approval processes and adapting intervention approaches to already-limited school hours and structures. The scientific community still needs to improve on the transparency of intervention approaches with regards to process outcomes, such as exposure time, the feasibility of intervention component delivery, and the acceptability of intervention components, in order to most effectively replicate and scale-up successful approaches to adolescent overweight and obesity prevention.  Institutional Review Board Statement: Ethical review and approval were waived for this study because the study did not involve primary human subjects research.