But there might be some new powerful ammunition for those who could do without the food the fast-food industry serves.
Researchers at George Washington University have linked fast-food consumption to the presence of potentially harmful chemicals, a connection they argue could have "great public health significance." Specifically, the team found that people who eat fast food tend to have significantly higher levels of certain phthalates, which are commonly used in consumer products such as soap and makeup to make them less brittle but have been linked to a number of adverse health outcomes, including higher rates of infertility, especially among males.
The danger, the researchers believe, isn't necessarily a result of the food itself, but rather the process by which the food is prepared. The findings were published in Environmental Health Perspectives, a journal funded by the National Institutes of Health.
"We're not trying to create paranoia or anxiety, but I do think our findings are alarming," said one of the study's authors, Ami Zota, an assistant professor of environmental and occupational health at George Washington University. "It's not every day that you conduct a study where the results are this strong."
(Update: A few hours after publication, Zota called to say that in reading her quote she felt that the word "alarming" was too strong a word to use to describe her findings. Rather, she said "striking" was more appropriate, because it conveys the magnitude of the findings without assigning a sense of urgency.)
In order to gauge how fast food affects the presence of certain non-natural chemicals, the team analyzed data for nearly 9,000 people. The data was collected as part of federal nutrition surveys conducted between 2003 and 2010. The surveys included detailed information about the participants' diets, including what each had eaten in the last 24 hours. They also contained the results of urine samples taken at the same time, which allowed the researchers to measure the levels of three separate chemicals.
For the purpose of the study, any food eaten at or from restaurants without waiters or waitresses was considered fast food. Everything else — food eaten at sit-down restaurants and bars or purchased from supermarkets and vending machines — was not.
The first thing the researchers found was that roughly one-third of the participants said they had eaten some form of fast food over the course of the day leading up to the urine sample collection. That proportion, high as it might seem, is actually in line with government estimates. In fact, more than a third of all children and adolescents living in the country still eat some form of fast food on any given day, a number that hasn't budged in decades, according to the Centers for Disease Control and Prevention.
The second thing the researchers found is that those participants who said they had eaten fast food in the last 24 hours tended to have much higher levels of two separate phthalates — DEHP and DiNP. People who reported eating only a little fast food had DEHP levels that were 15.5 percent higher and DiNP levels that were 25 percent higher than those who said they had eaten none. For people who reported eating a sizable amount, the increase was 24 percent and 39 percent, respectively.
And the connection held true even after the researchers adjusted for various factors about the participants' habits and backgrounds that might have contributed to the association between fast-food consumption and phthalate levels.
"We looked at it in so many different ways, and the effect still remains," said Zota.
The problem with these chemicals
There is little consensus on the harms of phthalates, which are widely used in commerce and give materials such as food packaging added flexibility, except that exposure to them "is widespread." But there is growing concern that the chemicals could pose a variety of risks, particularly when observed in the sort of levels seen in the study.
"There's a vast amount of scientific evidence suggesting certain phthalates can contribute to several adverse health effects," said Zota.
While there is less evidence that DiNP is problematic, some recent research suggests it very well could be. A study undertaken last year, for instance, found that exposure to the phthalate was associated with higher blood pressure.
For these reasons, many governments have moved to limit exposure to the industrial chemicals. Japan disallowed the use of vinyl gloves in food preparation for fear that their use was compromising health. The European Union, which limits the use of the chemical, has been nudging manufacturers to replace it. And the United States restricted its use in toys. In fact, the U.S. Department of Health and Human Services warned that DEHP is "reasonably anticipated to be a human carcinogen."
To fear or not to fear
The reason people who eat fast food seem to have much higher levels of potentially harmful industrial chemicals is unclear. But it's easy enough to guess: the sheer amount of processing that goes into food served at quick-service restaurants.
The more machinery, plastic, conveyor belts, and various forms of processing equipment that food touches, the more likely the food is to contain higher levels of phthalates. And fast food tends to touch a good deal more of these things than, say, the food one purchases at a local farmers market.
"I really hope this study helps raise public awareness about the exposure problems associated with our industrialized food system," said Zota.
Considering the prevalence of packaged food — and widespread exposure to phthalates (they can be detected in more than 98 percent of the population, per the CDC) — however, the takeaway isn't necessarily that fast food is toxic. Fast food, after all, isn't the only culprit here. Nor are less healthful things in general.
"It’s not fair to say, 'Oh, these exposures only happen if you eat unhealthy foods,'" Leo Trasande, an associate professor of pediatrics, environmental medicine and population health at New York University, told Bloomberg.
Anything that's gone through some form of processing or industrial packaging is vulnerable.
Still, given the new study's findings, it certainly seems as though eating fast food is more toxic than avoiding it, and not for the obvious reasons. Perhaps that's something many would have expected to hear, but it doesn't make it any less true.
"Traditional fast food was never meant to be daily fare, and it shouldn’t be," said Marion Nestle, who is the Paulette Goddard professor of nutrition and food Studies at New York University. "It’s too high in calories and salt and, as we now know, the chemicals that get into our food supply through industrial food production."