Method to Gauge Breast Cancer Risk May Be Flawed

Questionnaires may not reveal link to high-fat foods

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HealthDay Reporter

(HealthDay is the new name for HealthScoutNews.)

THURSDAY, July 17, 2003 (HealthDayNews) -- A research tool commonly used to determine links between diet and breast cancer could be seriously flawed.

That's the conclusion of a research letter that appears in the July 18 issue of The Lancet.

The method in question is known as the "food-frequency questionnaire," or FFQ. Researchers say defects in the basic methodology behind the questionnaire could mean it fails to reveal the association between dietary fat and the development of malignant breast tumors.

"We believe that, in the past, finding links between breast cancer and fat intake has been hampered by imprecise research methods which appear to have obscured a link between the two," says lead researcher Dr. Sheila Bingham, deputy director of the Medical Research Council Dunn Human Nutrition Unit in Cambridge, England.

A food-frequency questionnaire requires patients to rely on their memory to answer a series of questions designed to reveal their dietary habits during a specific time period. When combined with health history and medical data, the dietary information is analyzed and used to postulate links between what people eat and their risk of disease.

An alternate method of dietary calculation is the "food diary." Here, patients write down everything they eat for a specific period of time. That information is then used by researchers to calculate food-disease risk factors.

The food diary is the better way to go, Bingham's research contends.

"We believe that the comprehensive food diaries that our participants completed give a more accurate picture of eating habits compared to other methods," Bingham says.

Bingham's report comes on the heels of a July 17 report in the Journal of the National Cancer Institute. In that study, researchers used a series of food and lifestyle questionnaires -- not diaries -- that were completed over several years to document a positive association between high fat diets and breast cancer. However, previous studies using similar reporting systems have yielded conflicting results, causing a lot of controversy and leading some researchers to question if a link between dietary fat and breast cancer even exists.

For New York University breast cancer expert Dr. Julia Smith, Bingham's research letter offers an important new slant on why past research has met with such diverse results. And, she says, it may even help to explain how the controversy concerning study results started.

"We have always suspected a link between fat intake and breast cancer, but somehow the science could never fully verify that it was so," says Smith, a clinical assistant professor at the university.

"But now," she says, "as the new study points out, it's possible that the suspected association may have been partially masked by inadequate study methods -- specifically the FFQ -- which may not have been as reliable as we would have hoped."

While she believes additional research is needed to clarify if, in fact, FFQ results were equally flawed in other studies, Smith says the new finding could have some far-reaching implications in many areas of health -- not just breast cancer.

"If it turns out that the FFQ is not a reliable method of calculating dietary intake, then it could potentially affect at least some of the conclusions previously drawn between diet and many diseases, not just breast cancer," Smith says. And some of the current dietary recommendations could conceivably change, she says.

The new study involved some 13,000 women. At the start of the study, they each completed a food-frequency questionnaire, and most also submitted a more precise diary that listed everything they ate for seven days. The data were collected between 1993 and 1997.

By the year 2000, 168 of the women had developed breast cancer. At the time of their diagnosis, doctors analyzed the dietary data collected at the start of the study and compared it to data generated by the women in the study who remained healthy.

In looking just at the food diaries, Bingham found that the women who consumed the most fat (about 90 grams a day) were more than twice as likely to develop breast cancer than those who consumed fewer fatty foods (about 40 grams a day).

The surprising twist to the research became apparent when Bingham looked at the food-frequency questionnaires also completed by the women. Based on these answers, there appeared to be no association between dietary fat and cancer, even though Bingham says the women's food diaries -- and their medical history -- told a different story.

The only obvious conclusion, she says, is that the food-frequency questionnaires were simply not an accurate reflection of what the women were eating -- and more importantly, masked the obvious link between high-fat diets and breast cancer.

According to the entries in the diaries, the foods most likely to increase the risk of breast cancer include saturated fats -- which are found mostly in high-fat milk, butter, and meat -- as well as biscuits, cakes and other baked goods, Bingham says.

More information

To learn more about links between high-fat foods and disease and how to cut fat from your diet, visit the Mayo Clinic. To learn more about lifestyle factors linked to breast cancer -- and the debate over fat intake -- check with Cornell University.

SOURCES: Sheila Bingham, M.D., deputy director, Medical Research Council Dunn Human Nutrition Unit, Cambridge, England; Julia Smith, M.D., oncologist, clinical assistant professor, New York University School of Medicine, New York City; July 18, 2003, The Lancet

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