James Binkley, associate professor of agricultural economics at Purdue University, used state-by-state data to examine one bit of dogma in the war on weight -- that the nation's increasing fast food consumption is partly to blame for the widespread rise in adult obesity. He found that "states that have a lot of fast-food sales aren't the states that the Centers for Disease Control say have weight problems."
Binkley presented his findings at the annual meeting of the Western Agricultural Economics Association July 16 in Reno, Nev. The research was funded by Purdue.
"One conclusion that I would derive from this data is that changing exercise habits could be more to blame than diet," Binkley says. "It may be couch potatoes, not french fries, that are the heart of the problem."
There is little doubt that obesity is a burgeoning problem in the United States. Between 1960 and 1991, the number of adults who were overweight increased from 25 percent to 33 percent, according to the U.S. government's 1995 "Third Report on Nutrition Monitoring in the United States, Volume I."
Binkley compared data from the Centers for Disease Control's (CDC) Behavioral Risk Factor Surveys with the 1992 Census of Retail Trade using data for states and regions. This data was compared with the prevalence of fast-food restaurants in these states and regions.
The general assumption in media reports and among some nutritionists is that fast food leads to obesity, Binkley says. That is what Binkley expected to find when he compared the data. "It wouldn't have surprised me to find that there isn't any relationship at all at this level," he says. "But what we found was a slightly negative association. There certainly wasn't a positive relationship."
In other words, people living in states with high numbers of fast-food outlets were slightly less likely to be obese than people living in states with fewer fast-food outlets, according to the study.
According to Binkley, the study confirms that the problem of obesity is a confoundingly complex one. At most, the study suggests that the types of food one eats may not matter as much as the amount of calories consumed or the amount of exercise. "Fast-food restaurants may be to blame in some way for the nation's weight problems, but in general there is little evidence of that," he says.
Taking the study one step further, Binkley then compared the CDC data with the 1990 Sales Area Marketing Inc. (SAMI) data on warehouse grocery sales. Again, he found little correlation between types of food consumption and obesity.
"Actually, I couldn't find much of a relationship at all between long-term dietary changes and increasing obesity," Binkley says.
The data from the grocery wholesalers showed that populations that consume convenience foods and trendy foods such as jarred peppers or black olives are less likely to be obese than groups that consume more traditional foods such as canned goods, frankfurters or pudding.
Randy Gretebeck, a registered dietitian and exercise physiologist in Purdue's Department of Foods and Nutrition, says it's not uncommon for large studies to provide results that confound nutritionists. "Large studies have found that food intake doesn't seem to be a good indicator of obesity, but we know it should be. Also, recent studies have found that fat consumption has gone down across the nation, yet obesity continues to increase," he says. "Right now, more and more people are pointing to decreasing physical activity as a reasonable explanation."
Besides reduced activity and exercise, Gretebeck says, there may be other possible explanations for the seeming anomaly, "and what we really need to do is to investigate further."
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