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

Social Network Analysis

• Obesity can spread through social networks

Christakis and Fowler. NEJM 357: 370, 2007

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.

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.

Objective

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

Core Model

Social Network and Environmental Influences on Physical Activity

Sample Network

Network’s Influence

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

))1()1((||

1)(

tCtCF

Inf iFij

ji

C ti

Social Network and Environmental Influences on Physical Activity

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

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 (TPA, TEI)

– The impact on changing PA and EI if the threshold is exceeded (IPA, IEI)

– and network topology (small world, scale free)

Results

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.

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.