The childhood obesity epidemic has become a major public health issue internationally [1]. According to the World Health Organization, more than 340 million children and adolescents in the world had overweight or obesity in 2016, and the global prevalence of childhood obesity has sharply increased in recent years [2]. The childhood obesity epidemic is of major concern not only to Western countries but also to Asian countries [3]. Research has shown that the prevalence of childhood obesity was highest in Asia among developing countries [4]. Among Asian countries, the prevalence of childhood obesity in South Korea (hereafter ‘Korea’) is high [5], and a sharp rise in the obesity prevalence among Korean children and adolescents (hereafter ‘children’) was noted over the last 3 decades [6]. Nationally representative data from the Korean National School Health Examination survey using self-reported height and weight of survey participants showed that the prevalence of childhood obesity in Korea increased from 8.7% in 2007 to 15.0% in 2017 [7].

Previous studies found that childhood obesity in Korea is associated with body dissatisfaction [6], lower self-esteem, depression [8], asthma [9], lower health-related quality of life [10], insulin resistance, and hypertension [6]. In addition to the childhood obesity-related health problems, children with overweight or obesity may be at a greater risk of excess weight during adulthood [11]. This could lead to an increased risk of cardiovascular disease [12] and several malignancies such as colorectal cancer [13] over an extended period of time.

Although various interventions have been performed to prevent or treat childhood obesity in Korea, the overall effect of those interventions remains unclear [14]. Pediatricians in Korean generally recommend multidisciplinary behavioral interventions for the treatment of childhood obesity [14], but evidence for such a recommendation is based on studies [15-18] conducted outside of Korea. In Western countries, many meta-analyses have been performed to investigate the effect of obesity interventions among adults [19-24] and children [15-18,25-27]. Very few meta-analyses [19,28] have been conducted in Korea. Furthermore, these studies included both children and adults in the meta-analyses. None of the meta-analyses solely focused on obesity interventions for Korean children. Although a recent meta-analysis [29] was performed to analyze effects of obesity interventions conducted between 2000 and 2010, many of the studies included in this meta-analysis were outdated and did not directly measure individuals’ adiposity. Moreover, the meta-analysis had an insufficient number of studies on adolescents (i.e., only 3 studies included middle and high-school students), was missing quality assessment of included studies, and was missing subgroup analyses by age and sex.

Given the lack of recent studies, the purpose of this meta-analysis was to address this gap in the literature by quantitatively investigating the effect of obesity interventions for Korean children and adolescents. We also explored possible sources of heterogeneity among interventions, by documenting how individual (e.g., sex, age group, and baseline weight category) and intervention characteristics (e.g., intervention duration, number of intervention components, and type of intervention components) affect interventions’ effectiveness. Surgical and pharmacological treatments are beyond the scope of this meta-analysis, as we have focused on interventions geared toward lifestyle and behavioral modification.

Many interventions have been conducted to address childhood obesity in Korea. However, no reviews have been published that have compiled the scientific evidence about the effectiveness of childhood obesity interventions in Korea. To best of our knowledge, this is one of the first meta-analyses to examine the combined effect of obesity interventions in Korean children and adolescents. We also conducted subgroup analyses to explore possible source of heterogeneity. This review is important to help inform research, policy, and practice pertaining to childhood obesity interventions in Korea.

We found that, overall, intervention group children showed more favorable changes than control group children, as the 2 groups differed by 1.61 standard deviations. Our findings had the direction of effect that was consistent with earlier meta-analyses [25,29], but the magnitude of effect was notably greater than the one found in U.S. minority children (median effect size=0.16) [25]. Such difference may be attributed to the limitations of studies included in our analysis. We found evidence of publication bias, suggesting that obesity interventions in Korean children may have been unpublished if they showed small or negligible effect sizes, which in turn exaggerated the effect found in our analysis. This is consistent with findings of an earlier meta-analysis, which had relaxed inclusion criteria (therefore included data from interventions not published in scientific journals), showed no sign of publication bias, and had relatively smaller effect sizes [29].

Despite the number of moderators we explored in our subgroup analysis, most of those moderators were not statistically significant. We found that, in Korean children, obesity interventions had equal effect regardless of participants’ sex, age, and baseline obesity status, while an earlier meta-analysis among U.S. minority children suggested that interventions limited to children who already had overweight or obesity produced greater effect sizes [25]. We also found that intervention durations and the number of intervention components do not necessarily correspond with intervention effects in Korean children, while the meta-analysis among U.S. minority children found that interventions with 3–4 components were more effective than those with only 1–2 components [25]. While further studies are needed to understand why and how the effect of Korean interventions differs from that of U.S. interventions, clinicians must take additional precaution when making recommendations based on studies conducted outside Korea. Also, it should be noted that most of the interventions included in our analyses were intended for completion in less than a year, sometimes intended for just a couple of weeks. Considering how weight regain is common in years following obesity interventions [41], interventions lasting longer than 1 year may show reduced effectiveness compared to interventions included in this meta-analysis.

We found that selection of intervention components may be of greatest importance when designing obesity interventions for Korean children. We found evidence that a physical activity component should be included whenever possible, such that it helps intervention children escape sedentary lifestyle. However, the inclusion of a counseling component (e.g., professional guidance) and a family support component (e.g., parent’s involvement) must be done carefully, as they did not show the desired or intended effect. It is possible that interventions including counseling components were sometimes improperly implemented or failed to consider the factors that affect participants’ adherence (e.g., time needed to build rapport between children and counselor). Like this study, several U.S. childhood obesity studies [42-45] reported that counseling did not play an important role in pediatric obesity. However, unlike this study, a recent meta-analysis [46] that analyzed randomized controlled trials published in English from 2008 to 2018 showed that childhood obesity interventions with parental involvement produced larger effects than those without parental involvement. According to the World Health Ogarnization [47], parents play a vital role in encouraging their children to adhere to healthy eating and physical activity which in turn is related to favorable results in obesity prevention. It is important for health educators in Korea to provide parents with health education programs that help them understand the health risks of childhood obesity. Future strategies to curb childhood obesity among Korean children should consider the vital role of parents in the prevention and treatment of childhood obesity, and rigorous evaluation of parental involvement is needed using experimental studies that focus on this topic.

Limitations of this study should be acknowledged. First, this meta-analysis compared intervention and control groups using BMI changes as the study outcome, but the 2 groups were not compared using other measures (e.g., blood pressure, fat distribution, and presence of comorbidities like diabetes) that help the clinical diagnosis of obesity. While BMI is a commonly used measure of adiposity, it does not guarantee that individuals above a certain BMI threshold for obesity are truly unhealthy and have a diagnosable form of obesity. Similarly, we do not know if interventions that effectively reduced study participants’ BMI necessarily improve the health of those participants. Second, results of this meta-analysis were not corrected for age, and our subgroup analysis only compared 2 large age groups (children vs. adolescents). As intervention effectiveness may vary by intervention target’s precise age, our age-related inference may be limited. Third, inference related to “other” intervention component may be limited, as it includes methods that are not formally recognized as clinical intervention of pediatric obesity (e.g., acupressure). Regardless, these studies cannot be omitted, as they fit our initial inclusion criteria, and sensitivity analysis found that their omission does not significantly alter our results. Fourth, there was a sign of publication bias among included studies. We sought to minimize the effect of publication bias by using imputation; however, there is still a chance that this meta-analysis does not accurately reflect how the research findings truly are if we were to include studies that were unpublished or were published in other sources (e.g., thesis, dissertation, and commercial journals) which were not included in our search. Further investigations are needed to understand why many intervention studies on childhood obesity were unpublished in Korea. Lastly, this meta-analysis focused on quantitative synthesis, but provides no qualitative synthesis. Qualitative synthesis may provide further insight into why and how Korean obesity interventions differ from obesity interventions conducted in other countries. However, we only provided a table that summarizes study quality for assessing risk of biases. A review study with in-depth qualitative synthesis of Korean obesity interventions may be needed.

In conclusion, this study showed the effectiveness of obesity interventions for Korean children. Overall, intervention groups were strongly favored over control groups, consistent with what is suggested in the literature. Sex, age, baseline obesity status, and intervention durations did not significantly affect the BMI outcome, while interventions that include at least one physical activity component were significantly better than those that did not include any physical activity components. Despite what was suggested in the literature, we found that increasing the number of intervention components does not necessarily translate into increased intervention effects. The number of published intervention studies on childhood obesity is limited in Korea. Additional intervention studies, as well as follow-up meta-analyses, are needed to confirm findings of this meta-analysis.