Introduction: Research suggests obesity may be transmitted through social networks. A possible pathway is social influence on food choice. We investigated peer influence on the healthfulness of worksite food choices using social network analysis in a large hospital employee population, hypothesizing that socially-connected employees’ food choices would be correlated.
Methods: Data on all food purchases in 2016 were obtained from the hospital’s cash register database. The cafeteria system uses traffic light labels to mark foods as healthy (green), less healthy (yellow), or unhealthy (red). Employees’ food purchases were identified through the use of cafeteria debit cards; social ties among employees were inferred based on a validated algorithm using demographics and time/location of purchases. We used spatial autoregression (SAR) and generalized estimating equation (GEE) models to calculate associations between the proportions of employees’ and coworkers’ purchases that were labeled green (or red). SAR models assessed concurrent purchases of an employee and coworker, weighting the association between their purchases by the frequency and inferred strength of the social tie. GEE models assessed longitudinal relationships between purchases coworkers’ made in the presence of an employee in one 8-week period and the employee’s purchases in the next 8-week period. Food and beverages were analyzed separately. Models adjusted for employee and coworker confounders (age, sex, race/ethnicity, job type, education).
Results: In all, 5,118 employees used cafeteria debit cards to make purchases. Up to 536,240 employee/coworker interactions were observed, depending on the model (SAR, GEE) and outcomes (green/red, food/beverages). SAR models showed that a 1 percentage point increase in the network-weighted average of coworkers’ green-labeled (healthy) food purchases was associated with a 0.39 percentage point increase in an employee’s concurrent green-labeled food purchases (p<.001). Positive associations were also observed for red foods (0.20), and green (0.14) and red (0.31) beverages (all p<.001). Longitudinal GEE models showed that employees, as a population, increased purchases of green-labeled items by 0.013 percentage points on average when coworkers with whom they visited cafeterias in the prior 8 weeks increased their purchases of green items by 1 percentage point (p<.001). Similar associations were observed for red foods (0.013), and for green (0.006) and red beverages (0.020) (all p<.003).
Conclusions: Employees’ healthy and unhealthy food choices are correlated. Although one explanation is that people eat with others who have similar preferences, the longitudinal findings suggest that people create social norms for eating that influence peers. Worksite and other social networks may be novel targets for population-level interventions to promote healthy diet.