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Tuesday, July 22, 2003The study, published in this week's Lancet medical journal, was conducted at Cambridge University in England and involved 13,070 women who kept diet records from 1993-97. The researchers set out to discover whether the reason the previous follow-up studies found no link was that the method they used to examine dietary habits - a food frequency questionnaire - was too inaccurate. They also had the women keep a daily diary in which they recorded everything they ate. By 2002, 168 of the women had developed breast cancer. Each of those cases was matched with four healthy women of the same age who had filled out the questionnaires and diaries around the same time as the women who developed breast cancer had. The total group was divided into five equal categories of about 170, according to how much fat they ate each day. Two methods were used to place the women in one of the five categories; one based on the questionnaire and one on the daily diary. The researchers calculated separately for both methods the difference in breast cancer risk between the women who ate the least fat and those who ate the most fat. ``The effects just weren't seen with food frequency questionnaires,'' said investigator Sheila Bingham, deputy director of the human nutrition unit at Cambridge University. She called the questionnaire a ``very crude method'' that was not reliable. However, when the food diaries were used to categorize the women, those who ate the diet highest in saturated fat were twice as likely to develop breast cancer as those who ate the least. Of those in the lowest category, 14 percent developed breast cancer, compared with 20 percent, in the highest class. The more fat that was consumed, the higher the risk of breast cancer. The abstract of the study is here, but it doesn't shed much light on the subject. (Access to the entire paper requires a very expensive subscription.) Judging from the synopses of the study found in the papers, the only thing that can be said with certitude is that researchers aren't very good at measuring what sorts of food people eat, and how much. Surveys and questionnaires are known to be inaccurate methods of gathering information, so it's somewhat surprising to find that food frequency questionnaires are evidently the standard in nutritional research. So much so, that the "discovery" of their inaccuracy is making news. But what about the breast cancer and fat intake association supposedly found in this study? The evidence isn't all that impressive. For one thing, the sample size of women with breast cancer was very small - just 170. And within that small sample, the difference in breast cancer rates between those who ate the least fat and those who ate the most was also quite small - six percentage points. Then, there's the question of just how they gathered the food diary information. Did women record everything they ate everyday throughout the study? Apparently not: Women taking part in the study, the European Prospective Investigation of Cancer and Nutrition (EPIC), kept a food diary over seven days detailing what they ate, including brand names, and how much they consumed. Researchers then analysed the nutritional content of the diets and followed up the state of the women’s health up to seven years later. The diaries were completed during 1993 and 1997 by participants over the age of 45 and the results were assessed last September. Sorry, but one week in a life is hardly representative of a lifetime's dietary habits. Overall, it's a very weak case. Which is why on the same day, we're treated to news stories about pizza's cancer-fighting properties. posted by Sydney on 7/22/2003 07:24:00 AM 0 comments 0 Comments: |
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