It may seem intuitive that the more access people have to unhealthy food, the more likely they are to eat it and therefore to gain weight. For years studies have found that where a person lives can affect their access to healthy food, and some experts have drawn connections between being in close proximity to unhealthy food and weight gain.
But for Robert Wood Johnson Foundation (RWJF) Health & Society Scholars program alumnus (2007-2009) Jason Block, MD, MPH, the link is not so clear.
"As a physician, I know that obesity and weight gain are complicated," he says. "I thought that perhaps the story that's been told about this—that there's a clear link between body weight and proximity to food—might be a little bit premature."
Block is lead author of a study published in the November 15 issue of the American Journal of Epidemiology on the topic. His co-authors are RWJF Investigator Award in Health Policy Research recipients S. V. Subramanian (2009), PhD, MPhil, and Nicholas A. Christakis (2000), MD, PhD, MPH, as well as A. James O'Malley, PhD. Block is a general internal medicine physician at Brigham and Women's Hospital in Boston and an instructor at Harvard Medical School and the Harvard Pilgrim Health Care Institute.
Previous studies have been limited in that they only looked at populations at a snapshot in time, or used incomplete measures of proximity to food establishments, Block explains. His team of researchers attempted to overcome such limitations by taking a "very comprehensive look at the association" between proximity and body mass index.
They analyzed information gathered from the Framingham Heart Study Offspring Cohort, a group of people living in Massachusetts who have been surveyed and examined by researchers since 1971 as part of a longitudinal heart-health study. Using this readily available information, the research team was able to track where the cohort lived and their body weight over 30 years, providing a more accurate look at weight gain over time. Even after excluding subjects under age 21 and those who lived in nursing homes, did not reside in the Framingham area at the time of observation or had missing health data, the researchers had more than 3,000 subjects and 13,000 observations.
They also abandoned traditional neighborhood density measures and instead calculated driving distance from the subjects' residential addresses to food establishments in various categories: fast food restaurants, full-service restaurants, bakeries/coffee shops, supermarkets, grocery stores and convenience stores. Their longitudinal data accounted for both residential moves by subjects and the opening and closing of food establishments over time.
When all the factors were correlated they found no conclusive, consistent link between proximity to food establishments of any type—healthy or unhealthy—with individual body mass index.
They did find a small, statistically significant association for women who lived near fast food restaurants, but Block explains that because the association was so small they "don't believe it's very meaningful." Every kilometer (0.6 miles) a woman lived further away from a fast food restaurant was associated with a 0.50 kilogram decrease in body mass index. Finding an association for women but not for men could result from women having closer ties to their neighborhoods than men, he explains, and thus more directly influenced by the environment.
But proximity might not be the root cause of their weight gain. "We found this little link but the question is whether there's something more complex going on."
Block plans to continue his research on the subject by looking at workplace proximity to food establishments. Mapping out common routes to and from the cohort's places of work will allow researchers to more thoroughly examine how many food establishments subjects are exposed to each day. Researchers also will consider the subjects' dietary habits.
Underestimating Fast Food Calorie Count
Block has spent his career researching obesity, beginning at Tulane Medical School where he mapped the distribution of fast food restaurants in New Orleans. Now, with a new federal law in place to require chain restaurants to post calorie counts on their menus, he is working to evaluate its impact on consumers and rates of obesity. Block presented the first of his findings at the Obesity Society national meeting in October.
He and his colleagues have been surveying fast food restaurant patrons in four New England cities for the last two years, to find out what they are eating and why, and to gauge if they are conscious of the calorie counts of the meals they order.
Using information gathered from surveys conducted outside of five chain restaurants at lunchtime and after school, Block found that adolescents ages 11 to 20 consume about 750 calories on average at these establishments, but only estimate their meals to be around 450 calories.
"The underestimation exponentially increases with the size of the meal," Block says. "Their estimations are pretty good up to about 500 calories, but they're much less accurate with larger meals." The findings are also relatively consistent across all the restaurants, he says.
His team plans to continue collecting data and combine its findings for publication.