Having a fast food restaurant in the neighborhood may have little to no impact on the weight of adults who live nearby, according to a US study of more than 3,000 people.

The findings, published in the American Journal of Epidemiology, add to a conflicting body of research. A number of previous studies have suggested that people living in fast food-heavy neighborhoods have a higher obesity rate.

The latest study, led by Jason Block of Harvard Medical School, looked at 3,113 adults who entered a heart-health study in 1971, and followed them for 30 years. They found no consistent relationship between participants' driving distance to fast food facilities and their weight during that time.

"Maybe proximity is not the thing we should be focusing on," Block told Reuters Health, adding that it may be more important to look at why people make the choices they do at restaurants, grocery stores and other food outlets.

"In theory, you can make healthful choices wherever you go," he added.

The participants were about 38 years old on average when the study began. Over the next 30 years, they were interviewed and had physical exams seven times.

Block's team collected information on all restaurants, grocery stores and food outlets in the region over that time period, then calculated the participants' driving distance from home to the nearest restaurant or store.

The only evidence of a slight link between proximitys to a fast food restaurant and weight was among women.

On average, for each km (0.6 miles) women lived from the nearest fast food place, they showed a slightly lower body mass index (BMI), a measure of weight against height.

Researchers said that meant a woman would weigh about half a kg (one pound) less for each additional km of distance from a fast food restaurant.

The current study does not, though, mean that neighborhood food choices are unimportant, especially for lower income people, experts said.

In particular, having a good-quality grocery store nearby, meaning that people do not rely on convenience stores to shop, may make a difference in weight, said Lisa Powell, a senior research scientist at the Institute for Health Research and Policy at the University of Illinois at Chicago.

If a higher-income person does not live close to a supermarket, he can probably drive to one fairly easily. A lower-income person might be relying on public transportation, making the distance from quality food offerings an obstacle.

In any case, Block noted that fast food places are now "ubiquitous", meaning that having one close to where you live may no longer be of great importance.