The study, of the dining habits of nearly 5,000 Americans, dispelled the commonly accepted sentiment that fast-food restaurants like McDonald's and Burger King are the main contributor to higher obesity rates among the poor.
Paul Leigh, the study's co-author along with first author DaeHwan Kim, said the results surprised him.
Yeah, a little bit, because I thought it was going to be highest among the poor, Leigh told the International Business Times of fast-food restaurant attendance in a phone interview Friday.
I had the same idea that a lot of people did - that the poor are going to eat fast food more than other groups. That was my suspicion.
Instead, Leigh and Kim discovered that as income steadily rose, so did fast-food attendance and intake -- until it peaked at household income levels of around $70,000, Leigh told the IBTimes.
Fast food has long been thought to be the main cause of obesity among the poor. That's because conventional thought is that fast food is among the cheapest available to eat.
Leigh, however, explained why the findings make sense. He cited a classic example he has read in many economics texts, which goes like this: Both the poor and middle-class buy hamburger, but the middle-class is able to buy more hamburger. And moving up from the middle class, the upper-class starts to buy steak, because it tastes better and they can afford it.
This example goes along with the rise-and-fall curve his study projects. Leigh also said that from a business standpoint, the findings make sense.
This is crass to say, but poor people don't have a lot of money to spend, Leigh said. Why would you want to locate all your stores in the poorest areas? You want to locate them where there are more middle-class people than poor people. From a business standpoint, it makes more sense to locate restaurants closer to middle-class areas and cater to middle-class clientele.
Finally, Leigh said that people with lower incomes more easily qualify for food stamps, which are not redeemable at, say, a fast-food restaurant. They are redeemable, however, at grocery stores.
These reasons, Leigh said, made sense to him. It should also be noted that despite more conventional wisdom, fast food isn't exactly cheap.
The New York Times addressed the issue in September in a column titled, Is Junk Food Really Cheaper? In that article, it was written that a fairly average order for a family of four costs $28. Compare that to a roasted chicken, vegetables, salad and milk for a family of four -- it goes for about half.
It suggests that a higher ratio of the budget of the poor go to grocery stores, Leigh said.
The main question regarding the study's potential influence is its dated data set. Leigh and Kim used data from the 1994-96 Continuing Survey of Food Intakes by Individuals and the accompanying Diet and Health Knowledge Survey, both performed by the United States Department of Agriculture.
But because of the concepts he outlined in his reasoning, Leigh believes the research holds up today, and probably will hold up for some time unless some of the circumstances in his reasons changed.
The basic relationships that we found are still reasonable, especially since our findings coincide with so many other findings and data sets explaining consumption patterns, Leigh said.
Leigh and Kim concluded that fast-food restaurants are still a factor in obesity among the poor, but it's not a simple answer. For example, Leigh said, when people with lower incomes shop at grocery stores, soda is a popular option. It's cheaper than bottled water and, thus, appealing.
The study also found that men, people with more education, people that work more hours and smokers were more likely to opt for fast food than their counterparts.
Leigh and Kim's study -- titled Are Meals at Full-Service and Fast-Food Restaurants 'Normal' or 'Inferior'? -- is published online in the journal Population Health Management, and will be published in the December print issue.