1. Modeling the influence of social networks and environment on energy balance and obesity P Giabbanelli, A Alimadad, V Dabbaghian, DT Finegood ICO, Stockholm July 14, 2010

2. Social Network Analysis Obesity can spread through social networks Christakis and Fowler. NEJM 357: 370, 2007

3. Social Network Simulations Traditional interventions fail because they target individuals without consideration of their social network. Dieting with friends is ineffective compared to dieting with friends of friends. Bahr et al. Obesity (2009) 17, 723–728.

4. What spreads? Outcome or behaviour Previous studies have only considered the spread of obesity. Body weight is the product of food and physical activity related behaviours. Social network effects are only one type of environmental influence on food and physical activity behaviour. Marketing, the built environment, agricultural policy and many other factors also influence behaviour.

5. Objective To investigate the impact of social network and environmental influences on physical activity and energy intake.

6. Core Model

7. Social Network and Environmental Influences on Physical Activity

8. Sample Network

9. Network’s Influence where C is either physical activity (PA) or energy intake (EI) F is an individual’s set of friends

10. Social Network and Environmental Influences on Physical Activity

11. Change in Physical Activity where: I is the impact on physical activity (PA) T is the threshold that needs to be achieved to trigger change

12. Simulations To identify the relative contributions of specific factors we used a factorial design that tested all combinations of low and high values for: – Environmental influence (Env) – Thresholds for changing PA and EI (T PA, T EI ) – The impact on changing PA and EI if the threshold is exceeded (I PA, I EI ) – and network topology (small world, scale free)

13. Results

14. Conclusion Individuals are influenced by both their environment and their social network with a similar order of magnitude. While social network influences are important to changes in weight status, they should not be considered independent of other biological and environmental factors.

15. Acknowledgement This works was supported by the Canadian Institutes of Health Research (MT-10574) and the Modeling of Complex Social Systems Program (MoCSSy) at Simon Fraser University.