Adults who live close to fast food restaurants may not weigh any more than the rest of us, a new study suggests.
The findings, from a 30-year study of Massachusetts adults, add to a conflicting body of research. A number of studies have suggested that people living in fast food-heavy neighborhoods have a higher rate of obesity, while a few have failed to find a link.
But most of those studies have had limitations -- like only studying people at one time point, making it impossible to tease out whether easy access to fast food could be blamed for the extra pounds.
In this latest study, researchers used data from more than 3,100 adults who entered a heart-health study back in 1971. And they found no consistent relationship between participants' driving distance to fast food joints and their weight over the next 30 years.
There was some evidence of a link among women. On average, for each kilometer (0.6 miles) women lived from the nearest fast food place, they showed a slightly lower body mass index (BMI).
The translation: A woman of average height would weigh about a pound less for every additional kilometer she lived away from a fast food place.
"It was a very small effect," said lead researcher Dr. Jason P. Block, of Harvard Medical School in Boston.
"We interpret that as being not a very important association," Block told Reuters Health.
That is not to say that people's neighborhoods do not matter when it comes to health, Block said.
But, he added, the findings suggest that fast access to unhealthy food is not the key issue in the battle of bulge. "Maybe proximity is not the thing we should be focusing on," Block said.
It may be more important to look at why people make the choices they do at restaurants, grocery stores and other food places, according to Block. In theory, he noted, "you can make healthful choices wherever you go."
The findings, reported in the American Journal of Epidemiology, are based on 3,113 Massachusetts adults who enrolled in the study in 1971, when they were about 38 years old, on average.
Over the next 30 years, the participants were interviewed and had physical exams seven times.
Block's team collected information on all restaurants, grocery stores and other food outlets in the region over that time period. Then they calculated the study participants' driving distance from home to the nearest restaurant or store.
With that level of detail, and the long-term follow-up, the study "makes a significant contribution," said Lisa M. Powell, a senior research scientist at the Institute for Health Research and Policy at the University of Illinois at Chicago.
Powell, who was not involved in the research, has studied the relationship between neighborhood food options and people's weight.
And the current findings do not mean that neighborhood food options are unimportant -- especially for lower-income Americans, according to Powell.
In their own research, Powell and her colleagues have found that while there is no link between neighborhood food options and BMI overall, the picture was different in low-income areas. For low-income families, having a good-quality grocery store nearby -- rather than relying on convenience stores, for example -- may make a difference in weight.
If a higher-income person doesn't live close to a supermarket, Powell noted, he or she can probably drive to one fairly easily. For a low-income person, who would possibly be relying on public transportation, distance from quality food options could be a big obstacle.
The current study lacked data on people's incomes, so it wasn't possible to break the findings down that way.
And when it comes to fast food places, specifically, Block pointed out that they are now "ubiquitous." So the relative proximity of your house to the nearest McDonald's may simply not be a big deal.
Both Powell and Block noted that the interplay between people's environment, their personal behavior and their weight is complicated.
So the research questions go on. For Block's team, the next question is whether driving by fast food temptations on your way to and from work is related to the number on your bathroom scale.