There was a time when you had to be rich to be fat. Now you have to be rich to stay thin, says a new study.

Researchers led by Jennifer L. Black at New York University critically reviewed ninety studies published between 1997 through 2007 on neighborhood determinants of obesity through the PubMed and PsychInfo databases.

They found that neighborhoods with decreased economic and social resources have higher rates of obesity. They also found that residents in low-income urban areas are more likely to report greater neighborhood barriers to physical activity, such as limited opportunities for daily walking or physical activity and reduced access to stores that sell healthy foods, especially large supermarkets.

In order to organize the different approaches to assessing neighborhood-level determinants of obesity, the authors present a conceptual framework. The framework is intended to guide future inquiry by describing pathways through which neighborhoods might influence body weight.

Consisting of three inter-related layers, the framework includes the influence of social factors, access to quality food and exercise, and individual factors including behavioral intentions. Each level has indirect and direct influences on behavioral choices and may ultimately impact weight.

The authors conclude, “While individual-level characteristics such as income, cultural preferences, and genetic predisposition contribute to geographic disparities in weight, neighborhood-level services and structures that affect physical activity behaviors and dietary choices are emerging as important and potentially modifiable loci for public health intervention.”

This study is published in the January 2008 issue of Nutrition Reviews.