Obesity, defined as the abnormal or excessive accumulation of fat that poses a health risk, is one of the most significant global public health challenges of the 21st century. It is associated with increased risks of Type 2 diabetes, hypertension, and other cardiovascular diseases (Powell-Wiley et al., 2021). Numerous studies have investigated modifiable environmental determinants of obesity (Zhang et al., 2002, Jia, 2021), among which residential greenness has been identified as a protective factor (Jia et al., 2021; Lachowycz and Jones, 2011; Sarkar, 2017). For example, a study of 24,845 community-dwelling adults in Northeastern China found that an interquartile range (IQR) increase in residential greenness exposure was beneficially associated with a 20% decrease in the risk for obesity (Huang et al., 2020); another study in Chinese rural-dwelling adults suggested that an IQR increase in residential greenness exposure was linked with a 23% reduction in the risk for obesity (Jiang et al., 2022). Since obesity is a chronic multifactorial disease that can induce metabolic disorders (Heymsfield and Wadden, 2017), some studies have also focused on the benefits of greenness for metabolic disorders, to better prevent metabolic complications of obesity (Li et al., 2022; Tharrey et al., 2023). For example, a study of 15,477 community-dwelling adults in Northeastern China revealed that per 0.1-unit increase in greenness was consistently associated with an increase in high-density lipoprotein cholesterol (HDL-C) by 0.52% and a decrease in total cholesterol, triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C) by 1.52%, 3.05%, and 1.91%, respectively (Yang et al., 2019). However, most studies focused solely on the association of residential greenness with either obesity or metabolic disorders (Tables S1–S3), rather than specifically examining metabolic obesity.

Supplementing the investigation of obesity or metabolic disorders alone, obesity phenotypes have become increasingly important to stratify individuals in the clinical treatment of obesity (Kouvari et al., 2019; Stefan et al., 2013). Obesity accompanied by metabolic disorders, also referred to as metabolically unhealthy obesity (MUO) (Iacobini et al., 2019), may lead to dyslipidemia, hypercholesterolemia, insulin resistance, altered hormone levels, and changes in inflammation levels (Hildebrandt et al., 2023). Compared with MUO, individuals with metabolically healthy obesity (MHO) have approximately half the risk of developing Type 2 diabetes and cardiovascular disease, while they still have a significantly greater risk than those with metabolic unhealthy non-obesity (MUNO) (Magkos, 2019; Piche et al., 2020). These obesity phenotypes have been considered more accurate predictors for obesity-related complications (Piche et al., 2020). Although previous evidence suggested that obesogenic environments may contribute to the development of obesity phenotypes, few studies have investigated the associations between greenness and risks of different obesity phenotypes (Albuquerque et al., 2017; Reddon et al., 2016). Investigating associations between greenness and obesity phenotypes could help better understand the potential benefits of applying greenness interventions and provide precise suggestions for the prevention of metabolic obesity.

Long-term exposure to greenness in residential neighborhoods could affect individuals' health through several pathways, including improving individuals’ physical and psychological response to overloaded perceptual systems (James et al., 2016) and alleviating stressed neurohumoral regulation and negative emotions (James et al., 2016). More generally, there is a consensus that greenness can reduce harm from air pollutants (Franchini and Mannucci, 2018; Huang et al., 2020). A previous study suggested that air pollutants mediated 2.1%–20.8% of the greenness-obesity associations (Huang et al., 2020). The benefits of greenness may also be attributed to the lifestyles and behaviors that people shaped or conducted when being exposed to green space. According to the theory of neighborhood effect (Duncan and I, 2018), greenspace may help sustain and improve health by providing venues for physical activity (PA). A previous study suggested that PA mediated 1.18%–1.81% of the greenness-obesity association (Jiang et al., 2022), although inconsistent evidence exists (Fan et al., 2022). The evidence regarding the mediating effects of air pollution/physical activity on the association between greenness and obesity/metabolic disorders is either insufficient or inconsistent (Tables S1–S3). More empirical research is needed to estimate whether air pollution and PA level may mediate the effects of residential greenness on obesity phenotypes.

In addition, echoing a call for estimating moderating effects of sociodemographic status in the association between greenness and health outcomes (Markevych et al., 2017), there has been growing literature focused on the roles of sociodemographic status (e.g., age, sex, educational level, and urbanicity) in greenness-obesity associations (Fan et al., 2022; Huang et al., 2020; Sarkar, 2017). For example, females and the older are more likely to benefit from residential greenness than males and the younger due to various biological (e.g., sensitivity to endocrine-disrupting pollutants) and social (e.g., spending more time in surrounding green space) mechanisms (Fan et al., 2022; Sillman et al., 2022). Rural residents and those with poorer health literacy may be also more vulnerable to obesogenic environmental exposure due to less health knowledge and availability of health services compared to their counterparts (Fan et al., 2022; Markevych et al., 2017). Since the evidence of moderating effects of sociodemographic status is inconsistent (Markevych et al., 2017) and still limited in the association between greenness and obesity phenotypes, more evidence is needed to estimate their roles in various populations.

To address the aforementioned gaps (Fig. 1), we investigated the associations and potential pathways between residential greenness exposure and risks of obesity phenotypes using the China Multi-Ethnic Cohort (CMEC), one of the largest prospective cohorts in China (Zhao et al., 2021). We also estimated whether sociodemographic status moderated the associations between residential greenness and obesity phenotypes. As the World Health Organization (WHO) and other relevant agencies are increasingly emphasizing the importance of built environment and urban planning in addressing public health challenges in community settings (Organization, 2020), our findings would provide concrete evidence for multiple stakeholders, including health and environmental policymakers, to develop effective and innovative public health intervention strategies, such as adapting infrastructures to individuals with different obesity phenotypes for personalized motivation.