Book Review: Connected: The Surprising Power of Social Networks and How They Shape Our Lives by Nicholas A. Christakis and James H. Fowler

Double bacon cheeseburgers, milk shakes and your mother’s best friend’s brother can all make you fat. In Connected, social networking researchers Christakis and Fowler explain such effects by reviewing research into the ways even strangers may impact how you live, love and, yes, gain weight.

Social networking studies often rely on high-powered computers that model complex relationships. But in describing how such networks form and how moods and health practices can spread among members, the authors avoid technical language and jargon.

Some of the conclusions sound like common sense: People have less influence over others who are a few times removed than over intimate counterparts. And people with the most connections tend to have the greatest impact on group behavior. Other conclusions were counterintuitive: Health behaviors of a distant, same-sex friend can have a greater influence than those of an intimate, opposite-sex spouse.

Of course, showing how likely you are to gain weight once your mother’s best friend’s brother packs on some pounds doesn’t explain what causes the mutual ballooning. Perhaps his weight gain made a bigger waistline more acceptable in your social circuit. Or maybe he likes to take everyone out for burgers and shakes. The authors acknowledge the difficulties in untangling cause and effect in social influences.

Connected argues convincingly that it’s not enough to understand how individuals behave. The book details examples of how individual behaviors affect other members of a social network. In short, you are your brother’s keeper. And your mother’s best friend’s brother’s keeper, too.

Little, Brown and Co., 2009, 320 p., $25.99.