Childhood obesity has emerged as a major global public health concern, with recent estimates indicating that over 206 million children and adolescents aged 5–19 years are overweight or obese globally—a trend that has been accelerating in both developed and developing countries (1). Childhood obesity could persist into adulthood and is linked to a variety of detrimental health outcomes, including cardiovascular disease, complications, and mental health disorders (2, 3). Understanding the contributing factors to childhood obesity has become paramount for designing effective prevention and intervention strategies. Among the various factors implicated, dietary habits and physical activity (PA) levels have long been identified as key determinants of body weight regulation.

Dietary patterns, especially those rich in high-calorie, low-nutrient foods, are central to the rise in childhood obesity. However, growing evidence suggests that the gut microbiota, influenced by the consumption of dietary live microbes such as probiotics, may play an important role in metabolic health and weight regulation (4, 5). Live microbes are microorganisms that, when ingested in adequate amounts, confer health benefits to the host (6). Foodborne microbes’ composition influences the gut microbiota (7). In 2022, Marco et al. (8) quantified live microbes (per gram) for 9388 food codes contained in 48 subgroups in the National Health and Nutrition Examination Surveys (NHANES) database and categorized dietary live microbe intake into low, medium, and high levels. For this study, we focused on the combined moderate and high intake groups, termed “MedHi”. Negative links have been found between dietary live microbe intake and obesity or cardiovascular disease (9, 10). Yet, the impact of live microbes on childhood obesity remains inconclusive, and most existing evidence has examined live microbe intake in isolation, particularly regarding the interaction between live microbe intake and other lifestyle factors such as PA. This separate approach may overlook the potential for combined effects.

PA has long been acknowledged as a crucial factor in weight management due to its positive effects on energy expenditure, muscle mass, and metabolic function (11). Similarly, PA significantly influences the gut microbiota (12, 13). Supplementation with food-derived microbial communities, combined with active PA, may help alleviate systemic inflammation (14). However, the interaction between PA and the gut microbiome remains an underexplored area in pediatric research, and crucially, the combined role of PA and dietary live microbes has rarely been studied together. It is hypothesized that a combined approach, integrating both increased PA and dietary intake of live microbes, could have a more substantial impact on childhood obesity than either factor independently.

Therefore, the study aimed to explore the associations between dietary live microbe intake, PA, and the prevalence of overweight or obesity in children, specifically focusing on their combined effects. By addressing this gap, we hope to identify new strategies for promoting healthy weight in children, with the potential to reduce the long-term health risks associated with childhood obesity.

Our findings suggested that a high intake of live microbe and ideal PA levels were associated with lower odds of being overweight or obese. Furthermore, children who had both high live microbe intake and engaged in ideal PA exhibited the lowest prevalence of overweight or obesity. Importantly, the findings suggested a combined effect between live microbe intake and PA on body weight. In addition, children in the high live microbe and ideal PA group had the highest levels of enterodiol and enterolactone, which are intestinal microbial markers, and the lowest levels of CRP, an inflammatory marker. The findings highlight the potential synergistic role of diet and physical activity in preventing childhood overweight and obesity.

Our findings regarding the independent beneficial effects of dietary live microbes and PA align with a substantial body of literature (10, 26, 27). For instance, a randomized controlled clinical trial demonstrated that specific probiotic strains (HY7601 and KY1032) exert anti-obesity effects by modulating the gut microbiota (28), which resonates with our observation of a protective association. Similarly, the well-established role of PA in improving insulin sensitivity and reducing adiposity (29–31). However, the novel and central findings of present study is the significant combined effect between these factors. Directly comparable studies on this specific interaction in children are scarce. Our analysis suggests that the combined effect of high live microbes intake and ideal PA was associated with 35% lower odds of overweight/obesity (OR = 0.65). This suggests that studying these lifestyle factors in isolation, as most prior research has done, may underestimate their true public health potential. There are several reasons why previous studies may not have captured this synergistic effect. First, many interventions or observational studies focus exclusively on either diet or physical activity, lacking the statistical power or design to test for interactions. Second, the quantification of “dietary live microbes” is a relatively recent advancement (8). Without this standardized classification, previous studies could not precisely examine its role and interaction with other factors. Therefore, our study moves beyond the established independent effects and provides among the first pieces of large-scale, cross-sectional evidence supporting a combined lifestyle approach targeting both the gut microbiome and physical activity for pediatric obesity prevention.

Our findings of a combined effect invite an exploration of the potential bidirectional mechanisms linking dietary live microbes, PA, and the gut microbiota. We propose a physiological mechanisms framework wherein these factors interact with each other to combat obesity. On one hand, PA may create a more favorable gut environment for dietary live microbes to exert their benefits (32, 33). Furthermore, PA has shown to increase microbial diversity and the abundance of specific bacteria that produce short-chain fatty acids life butyrate (34). Butyrate not only reduces systemic inflammation and improves insulin sensitivity but also serves as the primary energy source for colonocytes, reinforcing gut barrier integrity (35). A stronger gut barrier prevents the translocation of pro-inflammatory bacterial fragments into the bloodstream, a key driver of obesity-related metabolic inflammation. Thus, PA may “prepare the ground” for ingested live microbes by fostering a healthier and more receptive gut ecosystem. On the other hand, a live microbe-rich diet may augment the metabolic benefits of PA. The short-chain fatty acids produced by gut microbiota from dietary fiber and other substrates can influence host energy metabolism. For instance, they can stimulate the release of gut hormones such glucagon-like peptide-1 (GLP-1), which promotes satiety and improves glucose homeostasis-effects that complement the improvements in insulin sensitivity induced by PA (36). Some microbial metabolites are also involved in mitochondrial biogenesis and fatty acid oxidation in skeletal muscle, potentially enhancing exercise capacity and recovery. Therefore, the synergy we observed may stem from a virtuous cycle: PA enriches a gut environment conducive to the beneficial actions of dietary microbes, while these microbes and their metabolites, in turn, amplify the metabolic and anti-inflammatory rewards of PA. This integrated model provides a compelling explanatory framework for our results and highlights the necessity of combining both lifestyle interventions for maximal effect in pediatric obesity prevention.

Enterodiol and enterolactone are not merely markers of microbial presence; they are bioactive metabolites produced specifically by the gut microbiota from dietary lignans found in whole grains, fruits, and vegetables (37). Their elevated levels in our combined group serve as an indicator of a functionally active and health-promoting gut microbiota. Byeong their known anti-inflammatory and antioxidant properties, these enterolignans have been specifically implicated in body weight regulation. Mechanistically, they are thought to modulate fat metabolism by activating peroxisome proliferator-activated receptors, which promote fatty acid β-oxidation and inhibit adipocyte differentiation, thereby reducing fat storage (38, 39). Conversely, CRP is a key mediator and marker of the low-grade systemic inflammation that is a hallmark of obesity pathophysiology. Adipose tissue, especially in obesity, secretes pro-inflammatory cytokines, which in turn stimulate hepatic production of CRP. Elevated CRP perpetuates a vicious cycle by further promoting insulin resistance and disrupting normal lipid metabolism, facilitating further weight gain and metabolic dysfunction (40). The significant reduction in CRP levels in the combined group indicates a potent attenuation of this obesity-driving inflammatory cascade. This anti-inflammatory effect likely stems from the combined actions of exercise-induced myokines and microbe-derived anti-inflammatory metabolites.

Given the increasing prevalence of overweight and obesity in children worldwide, identifying modifiable risk factors such as diet and PA is crucial for developing effective prevention strategies. Our study suggests that encouraging children to consume a diet rich in live microbes (e.g., through probiotics or fermented foods) and engage in regular PA may offer a complementary approach to obesity prevention. The observed reduction in CRP levels and the increase in intestinal microbial markers, such as enterodiol and enterolactone, provide a plausible biological basis for this synergy. To translate these findings into actionable strategies, policymakers and public health stakeholders could consider: (1) integrating the promotion of live-microbe-rich foods and regular physical activity into public health guidelines and educational campaigns; (2) fostering school-based programs that improve access to these foods and ensure adequate opportunities for physical activity; (3) prioritizing further research to strengthen the evidence base for these combined interventions. Incorporating these integrated lifestyle factors into public health initiatives and pediatric care guidelines could represent a promising strategy to help address the obesity epidemic.

Nevertheless, there are several limitations in our study that warrant consideration. First, the cross-sectional nature of our study precludes the determination of causality. The associations observed between dietary live microbe intake, physical activity, and overweight/obesity may be subject to reverse causation; for instance, children with obesity might alter their dietary habits or physical activity levels. Therefore, our results should be interpreted as identifying important associations rather than establishing causal links. Second, although we adjusted for a wide range of potential confounders, the possibility or residual confounding cannot be ruled out. Unmeasured factors, such as genetic predisposition, detailed dietary patterns beyond live microbes (e.g., total sugar or fiber intake), and psychosocial factors, might influence both the exposures and the outcome. This could mean that the protective effects we observed might be over- or under-estimated. Third, the assessment of physical activity relied on self-reported questionnaires, which are susceptible to recall and social desirability bias. This measurement bias could lead to the misclassification of participants’ true activity levels, which likely attenuates the observed associations toward the null, meaning the true protective effect of physical activity might be stronger than what we reported. Finally, regarding the generalizability of our findings, the NHANES data are nationally representative of the non-institutionalized US population. Therefore, our results are likely generalizable to children and adolescents in the United States with similar demographic characteristics. However, caution should be exercised when extrapolating these findings to populations with substantially different genetic backgrounds, dietary cultures, or built environments that influence physical activity. The specific food sources and definitions of “dietary live microbes” are based on the US food supply, which may not directly translate to other countries.

Beyond the methodological considerations, translating these findings into real-world public health recommendations faces several practical challenges. First, to some extent, ensuring consistent adherence to a diet rich in live microbes can be difficult. Factors such as taste preferences, dietary habits established in childhood, and the higher relative cost and lower accessibility of certain fresh and fermented foods in underserved communities are significant barriers. Second, promoting and maintain ideal levels of physical activity requires addressing issues related to the increasing sedentary lifestyle, screen time, and access to safe recreational spaces. Therefore, successful implementation would likely require multi-level strategies that extend byyond individual education. These could include public health policies to improve the affordability and availability of healthy foods, creating more community-based physical activity programs, and educational initiatives that engage both children and their families to foster sustainable lifestyle changes.

Our study provides evidence that the combination of adequate dietary live microbe intake and ideal physical activity offers stronger protection against overweight and obesity in children and adolescents than either factor alone. This finding fills an important gap in the pediatric literature by highlighting a synergistic approach to obesity prevention. To translate these findings into practice, future public health strategies and clinical advice should move beyond isolated recommendations and promote the integrated adoption of both behaviors. While further longitudinal studies are warranted to establish causality and elucidate the underlying mechanisms, our findings underscore the potential of a combined dietary and physical activity strategy as a foundational element in combating childhood obesity.