No significant associations between meat intake and premenopausal breast cancer were observed in the population-based case-control study. Several studies have suggested that the factors that promote pre- and postmenopausal breast cancers may differ, and research is unclear about whether meat plays an equal role in both cancers. It may be that the kind of low-level genetic/cellular damage related to meat consumption builds up slowly, and only develops into cancer over the course of decades.
Small, Steady Changes Can Lower Risk, Experts Say
This damage can be prevented, and it’s not necessary to eliminate meat from the diet completely to do so, according to AICR. The cancer experts recommend shifting the focus of the typical meal away from meat and onto plant foods.
“It’s as simple as making a few small adjustments to how your dinner plate looks tonight,” said Collins. “It doesn’t have to be drastic: simply add another kind of vegetable and cut back on the amount of meat a little. Gradually let vegetables, fruits, whole grains and beans take up more space on the plate so meat ends up with less.”
This is the approach behind AICR’s New American Plate campaign, which offers free, recipe-filled brochures and health aids to help Americans make and maintain these healthy changes.
Scientists Analyze Data on Cooked Meat, Breast Cancer
In the new Epidemiology study, researchers examined data from the Long Island Breast Cancer Study Project, a large case-control study. Women diagnosed with breast cancer between August 1996 and July 1997 were identified by medical records and asked to participate in the study. These “cases” were matched with “controls”—women who resemble the breast cancer patients in attributes like age and sex but who have not been diagnosed with breast cancer.
Each of the 1,508 cases and 1,556 controls met with an interviewer who administered a questionnaire on a range of subjects (medical history, level of physical activity, smoking status, etc.); the women also answered a detailed dietary intake survey.
The researchers then grouped and analyzed the data according to the amount of grilled, barbecued or smoked meat the women estimated they’d consumed over their lifetimes, and in the four weeks prior to the interview.
Grilling Carcinogens Apparently Long-Term, not Short-Term, Risk
The researchers then took their analyses a step further. From the data provided about frequency of meat intake, the method of its preparation, and its level of doneness, they calculated the total amount of exposure the women had experienced (in the one year before their interview) to various carcinogenic substances known to arise in cooked and smoked meats.
These values for exposure to heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) were grouped to allow the researchers to compare high intakes to low intakes, but no links were seen between breast cancer risk and the amount of these carcinogens the women had consumed in the previous year.
The authors suspect this reflects the fact that dietary risk factors exert their influence over a lifetime, not within the span of a single year.
Also not found in this new study, even in the long-term data: any evidence of a link between grilled chicken or fish and pre- or post-menopausal breast cancer. One potential explanation for why the observed association only shows up for “red meat” (beef, pork, lamb) is the existence of a form of iron called “heme” iron in these foods. Heme iron (which, as the name suggests, is found in the blood) is found only in animal foods, and the amount in beef, for example, is about twice that in chicken and fish.
This association remains theoretical, particularly in regard to breast cancer, although heme iron has been shown to damage the lining of the colon and cause the kind of abnormal cell growth that can lead to cancer.
More Research Needed, but Evidence is Building
The study in question is a case-control study, and it is only one way that researchers investigate the association between diet and cancer risk. Case-control studies have particular strengths and weaknesses, and you can read more about how researchers fit case-control data into the “big picture” of the diet-cancer link here.
In their discussion, the authors of the new study discuss several limitations inherent in the case-control method of investigation. Case-controls are dependent on the response rate of participants (82 percent of “cases” participated, compared to 63 percent of “controls”, in this study) and the ability of participants to recall their diets accurately.
The researchers also examined potential “confounders” (variables that may be independently associated with cancer risk, such as physical activity and alcohol use). They believe it unlikely, however, that any “residual confounding” (the sort that persists in studies after all attempts to correct for it) could explain the significant associations observed.
Future, larger studies are needed to confirm the specific links between meat, method of preparation and breast cancer. But it’s worth noting that evidence linking diets high in meat and low in plant foods to greater breast cancer risk is mounting steadily.
The new Epidemiology study comes on the heels of last month’s findings from a large cohort study published in the April issue of the British Journal of Cancer that linked high red meat consumption to a 56 percent increase in breast cancer risk, and major results from the Nurses Health Study II published in the Annals of Internal Medicine last November showing that meat consumption was linked to increased risk for estrogen-positive breast cancer.
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The American Institute for Cancer Research (AICR) is the cancer charity that fosters research on diet and cancer and educates the public about the results. It has contributed more than $82 million for innovative research conducted at universities, hospitals and research centers across the country. AICR also provides a wide range of educational programs to help millions of Americans learn to make dietary changes for lower cancer risk. Its award-winning New American Plate program is presented in brochures, seminars and on its website, www.aicr.org. AICR is a member of the World Cancer Research Fund International. |
