The role of social networks in the development of overweight and obesity among adults: a scoping review

One of the pathways through which weight might be shaped by an individual’s social network is through mirroring the behaviour of significant others within one’s social network. This pattern was visible within friends and family networks, peer networks and cultural groups. One of the ways in which this process was explicated was through the development of eating practices in a family setting. For example, amongst obese African-American women, Befort et al. [32] found that cultural practices (such as preferences for certain foods) that were embedded within social networks influenced food choices. Within qualitative interviews, the women in this study made a strong connection between food choices and social affiliation, arguing that their eating habits bound them to their familial networks. Similarly, through qualitative focus groups, Bertoni et al. [33] observed social pressure amongst African Americans to conform to dominant food habits within family networks. Family tensions that arose when women differentiated their food practices from those of other family members were described as a barrier to making dietary changes. Other studies indicate that individuals sometimes mirror the behaviour of others with whom they have minimal social contact. In two similar experimental studies, McFerran et al. [34] and Burger et al. [35] observed that female undergraduate students in the USA base their food choices on those of others in their immediate social environment. These studies both indicated that choice of snack and snacking portion size was likely to be matched to the choices of others in a similar setting. Interestingly, Pachucki et al. [36] found that consumption of alcohol and snacks was more likely to be influenced by the consumption of similar items by others within one’s social network (friends, family and spouse) than other foods.

Similar results have been shown for physical activity norms across a range of different social settings and these patterns were particularly common within peer groups. Military trainees, for example, were likely to try and emulate the fitness levels of those in their peer groups [37]. Difficulty maintaining cultural norms within particular social settings has also been identified as a barrier to physical activity among Emirati women who perceived that walking alone in a public space for physical exercise was seen to contravene social norms [38]. A quasi-experimental study in the USA by Lemon et al. [39] indicates that workers often mirror the dietary and physical activity behaviour of their colleagues. Hospital workers who perceived that their colleagues ate healthily and undertook physical activity were more inclined to do the same. Other studies more explicitly demonstrate that mirroring might be linked to a desire to be accepted by particular groups. Indeed, Robinson et al. [40] found that desire for social acceptance may be an underlying cause of mirroring the portion size of those around us. These authors found that food mirroring between peers could be predicted by levels of self-esteem and social sense of empathy, indicating that those with less cultural competence might be more sensitive to the behaviour of others. Hruschka [10] has proposed that dietary and physical activity behaviour might be mirrored, through a process of seeking approval, even when body weight norms are not shared, but the cross-sectional study established to test this theory provided no evidence to support such an explanation. There is some indication that participating in organised clubs and organisations might reinforce bodyweight or physical activity social norms, for example Kouvonen et al. [41] found that older adults who participated in social activities were more likely to maintain a healthy body mass index (BMI) than older people who did not participate.

A range of different studies explored the ways in which body size aspirations are developed through social networks. Different types of networks have been shown to be important but peer networks seem to be particularly influential here. In a randomised controlled trial, Krones et al. [42] found that being around people that are thinner than average increased body weight dissatisfaction amongst young American women. Several studies suggest that the cultural group with which one identifies is important in shaping ideals. These cultural groups can reflect ethnicity or education level. In a qualitative cross-sectional study conducted in Australia, Renzaho [43] found that immigrant parents sought to modify their children’s weight in response to the cultural ideals of their country of origin while children sought to challenge the strategies of their parents in an attempt to conform to the perceived ideals of their Australian peers. Using survey data from North America, Hruschka [10] found evidence to indicate that friends’ body size has an influence on an individual’s body weight ideals. The study indicated that although friends do not necessarily share ideas about body size norms, their ideals may become aligned through friendship. Other studies indicate that body size norms can be established through social networks. In the USA, Bramble et al. [44] found that decisions about healthy weight were made in the context of one’s extended social network and particularly the ethnic group with which one identifies. Blanchflower et al. [45] found that perceptions about overweight among Europeans were influenced by comparisons with others and that educated individuals were more likely to rate themselves as overweight, indicating that this group aspires to a thinner ideal. Similarly, motivation for weight loss has been shown to be influenced by perceptions of the weight of one’s peers. Chandler-Laney et al. [46] showed that female participants on a weight loss programme who perceived most women their own age to be overweight lost weight more slowly (and gained weight more quickly after the intervention) than women on the programme who perceived their peer group to be slimmer. These patterns were stronger amongst European American than African American women and seemed to be mediated by the extent to which participants consciously restricted their dietary intake, which, as the authors suggest, might indicate that women who perceive their peers to be overweight are less inclined or able to restrict their diet. Related to this, American undergraduates have been shown to calculate their risk of becoming overweight through comparison with others they identify with, defined as friends or average same-sex undergraduate peers, irrespective of absolute risk [47]. A mixed methods study in a similar setting has indicated that gaining weight upon starting university is often seen as inevitable, based on anticipation that this is the norm for people their age [48].

Comparisons with others in an ephemeral network can influence dietary choices. Amongst female undergraduates in the USA, McFerran et al. [49] found that food choices were influenced by the body weight of people present in the immediate setting and this seemed to be directly related to an individual’s comparison to others in the setting. In this quasi-experimental study, non-dieters consumed a larger quantity of snacks when served by a thinner, rather than heavier waitress, whereas dieters ate more when the waitress was heavier. Dieters were also more likely to respond to food recommendations from a heavy waitress (for healthy and unhealthy food choices) than they were to a slim waitress. Similarly, the intensity of an individual’s desire to eat has been shown to be influenced by the body weight of others in the immediate setting, with observation of an obese eater decreasing appetite [50].

The sense of belonging that people have within particular communities seems to influence weight and weight influencing behaviours in a number of different ways, depending on the cultural setting. This is most prominent within networks of friends and family and networks of people living within the same geographical region. In a longitudinal study in an Amazonian village, increased gift giving and communal work was associated with higher BMI [51]. By contrast, in North America, Veenstra et al. [52] and Holtgrave [12] both found that involvement in community organisations and public affairs, volunteerism, informal sociability, and social trust) were protective factors in the development of overweight and obesity. This indicates that sense of belonging is important but that other forms of social capital might influence obesity. One of the ways in which sense of belonging might influence obesity is through a greater sense of the value in protecting one’s health. Amongst public sector employees in Finland, a greater sense of togetherness, trust and co-operation in the workplace has been shown to reduce risk behaviours for overweight and obesity (smoking, heavy drinking and physical inactivity [53]. Similarly, a sense of being part of one’s community has been associated with greater interest in physical activity in the USA [5] and a sense of community belonging amongst one’s neighbours made people more likely to undertake behaviour change in relation to weight influencing behaviours in Hystad and Carpiano’s [54] survey of behaviour change in Canada. Both social isolation and loneliness have been associated with a greater risk of being inactive amongst adults in the UK in a longitudinal survey of physical activity levels [55]. These findings have not been replicated in all settings: in their survey of Australian adults Christian et al. [56] found no association between BMI and neighbourliness or BMI and neighbourhood cohesion. They did however find some evidence to suggest that perceptions of community safety and the amount of graffiti are associated with BMI. Similarly, challenging the notion that social isolation might increase one’s chances of becoming obese, Pollard et al. [57] found little evidence of an association between social network size and waist circumference in the UK.

Social support, accessed through friends and family networks, has been linked to higher self-efficacy in online support networks for diet and physical activity interventions: social support seemed to provide structure, encouragement and purpose in relation to physical activity in a study of motivation amongst individuals with schizophrenia [58]. Similarly, in a study of undergraduate students in the USA [59], individuals’ levels of exercise could be predicted by that of their friends but only when support from such friends was rated as high. Amongst overweight women in the post-partum period in the USA, social support (and expectations about such support) were shown to influence healthy behaviours [60]. Most specifically, lack of social support was identified as a barrier to weight loss in this study. These findings were echoed in a study by Mackert et al. [61] where USA adults reported that family members could undermine their attempts to implement healthy behaviours. Through qualitative methods in a similar setting, Daniels [62] provides insight into how this might be experienced, demonstrating that family demands make it harder for women to prioritise weight loss. Similarly, a study in the USA [63] found that women on low incomes with large families who did not receive support from their parents were more likely to obese that those with smaller families who had parental help but social support has not been consistently linked to higher BMI [64]. Relatedly, based on a review of literature, Sobal [65] has argued that it is more difficult for people who are overweight to develop romantic relationships or to maintain social networks due to a lack of social support. It might be difficult to put these findings into practice, however: a review of the evidence relating to social support in weight loss interventions found inconclusive evidence to detect the influence of social support on intervention outcomes [66].