Previous studies have examined the relationship between residential density and overweight/obesity, but the findings have been contradictory (Doyle et al., 2006; Ewing et al., 2003; Lopez-Zetina et al., 2006). Some studies have found a negative relationship between residential density and overweight (Garden & Jalaludin, 2009; Rutt & Coleman, 2005), while others have not found any significant association (Kelly-Schwartz et al., 2004; Pendola & Gen, 2007). A study conducted in China by Wang et al. (2019) found that individuals living in neighborhoods with low and medium residential density were at a higher risk for overweight compared to those living in neighborhoods with higher residential density. Taking gender into accounts, this association was only significant for men. In contrast, another study in China found that adolescents living in neighborhoods with higher and medium residential density were more likely to be overweight compared to those living in neighborhoods with lower residential density (Xu et al., 2010). Furthermore, a study conducted in metropolitan areas of Vancouver and Portland showed that traffic and neighborhood cohesion had an inverse effect on adult physical activity in neighborhoods with higher residential density (Chaudhury et al., 2012). It has been suggested that higher residential density can lead to increased traffic congestion up to a certain threshold, beyond which walking and cycling become more comfortable (Forsyth et al., 2007). Overall, the relationship between residential density and overweight/obesity is complex and can vary depending on factors such as gender, age group, and the specific context of the study. Further research is needed to better understand the mechanisms behind this relationship and to account for potential confounding factors.
Several studies have investigated the relationship between public transportation and obesity, and have consistently found a strong association. Brown et al. (2017), Flint et al. (2016), MacDonald et al. (2010), Martin et al. (2015), and Webb et al. (2016) all examined the changes in body mass index (BMI) associated with public transportation. These studies found that using public transportation was linked to a decrease in BMI. These studies can be divided into two groups based on their focus. The first group examines the level of using public transportation and its association with obesity. The second group explores the accessibility to public transportation and its relationship with physical activity and obesity (Richard Patterson et al., 2019). According to Brown et al. (2019), investing in improving access to public transportation can reduce mortality associated with transportation and the burden of diseases related to physical inactivity and obesity. Some studies have examined the relationship between distance from a participant's home to the nearest bus route and obesity, with mixed findings. Sun et al. (2017) found a negative association between the mentioned distance and body mass index in China, while Hirsch et al. (2014) found no association in the United States. With regard to the second group, Laverty et al. (2018) found that both initiating and increasing use of public transportation are associated with increased physical activity and lower obesity among women. R Patterson et al. (2019) indicated that one-third of public transportation users engage in more than 30 minutes of physical activity, with rail users averaging 28.1 minutes and bus users averaging 16 minutes.
In recent years, there has been a growing body of research exploring the relationship between green space and various health outcomes, including physical activity, obesity, and cardiovascular diseases. These studies have investigated different aspects of green space, such as the ratio of green space in neighborhoods (Dempsey et al., 2018; Pietilä et al., 2015), greenness measured using the normalized difference vegetation index (Dadvand et al., 2016; O'Callaghan-Gordo et al., 2020), distance to the nearest green space from residential areas (Ghimire et al., 2017; Pietilä et al., 2015; Tamosiunas et al., 2014), and green space density or per capita (Carlson et al., 2012; Galvez et al., 2013; Ghimire et al., 2017; Young et al., 2014). Some studies have found positive effects of green space on reducing obesity rates. For example, research has shown that an increased number of parks, green belts, and open spaces is associated with higher levels of weekly walking and reduced risk of overweight and obesity among women (Meurs & Haaijer, 2001; O'Callaghan-Gordo et al., 2020). Access to green space has also been linked to increased levels of moderate to vigorous physical activity, reduced sedentary behavior, and a lower risk of overweight or obesity for women (Astell-Burt et al., 2014). Additionally, proximity to green spaces has been associated with higher levels of physical activity in older adults (Dadvand et al., 2016), as well as improved cognitive health in this population (Broekhuizen et al., 2013). Forest coverage has also been found to be related to lower overweight rates and lower body mass index at the county level (Boncinelli et al., 2015; Ghimire et al., 2017). However, the findings regarding the relationship between green space and health outcomes are not always consistent. Some studies have found no association between park improvements in neighborhoods and physical activity (Cohen et al., 2009). Similarly, no direct relationship has been observed between residence in greener areas and increased overweight and obesity (Cummins & Fagg, 2012). Other studies have also failed to find a significant association between green space and body mass index among older adults (Broekhuizen et al., 2013; Sander, Ghosh, & Hodson, 2017), or between natural amenities and the prevalence of obesity and physical activity in non-metropolitan areas in the United States (Michimi & Wimberly, 2012). Overall, these differences can be partially explained by various factors such as different indicators, the mismatch between perceived and objective measures, self-selection, different scales, gender changes, and age groups.