Volume 49, Number 1, Spring 2000

HOT DOGS CAUSE CANCER -- OR MAYBE THEY DON'T; WHO'S COUNTING WHOM?

by Lawrence Lindner

How often, on average, did you eat a quarter of a cantaloupe during the past year? One to three times a month? Once a week? Two to four times a week? Once a day? Please try to average your seasonal use over the entire year. For example, if cantaloupe is eaten four times a week during the approximately three months that it is in season, then the average use would be once a week.

A little confused? The cantaloupe question is just one of hundreds you'd have to grapple with if you were participating in Harvard University's Nurses' Health Study, from which dozens of associations have been made about food and disease-and then reported on in the media.

And, the Nurses' Health Study is just one of dozens of research projects that you read or hear about every year, where scientists make correlations between the frequency of foods eaten and the frequency with which the eaters end up with various diseases. But do the eaters, in the end, manage to report their food consumption accurately?

Writes University of Leeds psychologist John Blundell in a recent issue of the American Journal of Clinical Nutrition: "It is now freely admitted that most databases do not inform us well about the actual foods that individuals habitually consume because of the massive problem of misreporting."

David Allison, an associate research scientist at St. Luke's-Roosevelt Hospital Center in New York, puts it more bluntly: "The measurements by questionnaire of what people eat are just terrible." To drive home his point, he notes that "I actually know two men who are in the Nurses' Health Study. These guys confessed to me that their wives are nurses, and they [the husbands] fill out the food questionnaires."

Blundell, for his part, cites a just-published study in which a group of obese men underreported their typical calorie intake by 36 percent.

Truth be told, underreporting of calories is an old story: Nutrition researchers have known for years that overweight people slash calories from their daily diets-on paper, at least-when asked in studies how much they eat. But now they're underreporting fat consumption, too-as did the obese men in the study cited by Blundell.

Blundell isn't surprised. "The more we tell people that they should reduce the amount of fat in their diets," he writes, "the more they tell us how little of it they eat."

Referring to all the room for error in study participants' acknowledgment of what and how much they eat, Blundell says, "We should be cautious about making too many doctrinaire statements on nutrition-disease relations on the basis of data that may be seriously flawed."

And it gets more complicated still. Studies in which people are first asked to report what they eat and are then followed to see what diseases they develop can, at best, report only associations between foods and illnesses. By their very nature, they could never tease out cause and effect, even if people could accurately report their food intake.

Take, for example, a 1994 study conducted by a researcher from the University of Southern California and reported in the Washington Post with the headline "Study Links Hot Dogs, Cancer: Ingestion by Children Boosts Leukemia Risk, Report Says." The first sentence of the article read: "Children who eat more than 12 hot dogs per month have nine times the normal risk of developing childhood leukemia."

While this sounds as though hot dogs cause leukemia, all that was actually found was that hot dogs and leukemia somehow went together. Maybe it was the buns-or the mustard or relish-or something entirely unrelated to the children's eating habits. Add to that the fact that the study relied entirely on parents' recollections of how many hot dogs their children had eaten (recollections that sometimes went back years), and the link becomes more tenuous still.
For better or for worse, however, the what-do-you-eat research efforts often get more play in the media than other kinds of nutritional studies. Alice Lichtenstein, a heart disease researcher at Tufts University, says that's because they are simple to understand.

"They ask relevant questions that the everyday person is interested in," such as what type of eaters get cancer and what type get heart disease. "But the everyday person," she says, doesn't always understand the difference between a factor causing a disease and a simple association with a disease.

Sometimes scientists aren't thinking clearly, either. James Fleet, a nutrition researcher at the University of North Carolina at Greensboro, says scientists can get carried away by their own results and read more into them than is there.

Not that Fleet or other researchers believe food-questionnaire research isn't important. "It's highly important," Fleet says, because it "generates new hypotheses to test in more controlled settings."

But the results of such studies should be taken "with a considerable grain of salt" by the lay community, says Allison. While findings from such research are often interpreted as "you should do something about this now," he says, "that's not where it's at. It doesn't produce guidance about what to do today-eat more of this, less of that."

Tufts's Lichtenstein agrees. What people should think when they read about such research, she says, is, "Well, gee, that's interesting. I'll file that in the back of my head and wait for more studies to come out."

If more studies do come out and the data start to crystallize, says Allison, "The USDA will make a statement. The American Heart Association will make a statement." In other words, health-promoting organizations will provide dietary guidance based on the totality of evidence rather than on the results of this or that study in which people couldn't accurately report what they ate, anyway.

Even nutritional epidemiologist Katherine Tucker of Tufts, who conducts studies by asking people what they eat, sees it that way. "A new finding is news," she says, "and I think it should get out there. But it doesn't mean you should take it as dietary advice. Look at the body of accumulated evidence."

Lawrence Lindner is a freelance writer in Hingham, MA, who writes regularly for the Post. Special to the Washington Post, Feb. 1, 2000. Copyright 2000, the Washington Post Company.