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Vol. 07 Issue 2, Spring 2002

Vegetarian Eating and Breast Cancer -- Evaluating the Evidence
The Ribbon 

Carol Devine, BCERF Education Leader and Associate Professor
Division of Nutritional Sciences

A recent headline declared that being vegetarian was linked to having a lower risk of breast cancer. Like many of you, I found this headline intriguing and went to the original article to see for myself. Some questions I considered as I read were:

Who was studied? The researchers recruited women up to 75 years of age who had been born in South Asia (India, Pakistan, Bangladesh) and later immigrated to England. Some of these women had been lifelong vegetarians, avoiding meat and eggs but consuming milk. Other women had been meat eaters, except for pork.

What was the study design? This was a case-control study. The diets of women diagnosed with breast cancer within the past 2 years (the cases) were compared to the diets of women with similar characteristics and living in the same area who did not have cancer (the controls).

What was the research question? Was breast cancer incidence less likely among women who had been lifelong vegetarians compared to women who had been meat eaters?

What data were collected? Women were asked what they had customarily eaten 2-3 years before they were interviewed (before cancer diagnosis among the cases). They were also asked about other breast cancer risk factors (e.g. family history of breast cancer, body weight etc.)

What were the findings? Women who were lifelong vegetarians were only slightly less likely to have had breast cancer than women who were meat eaters. In addition, the difference in breast cancer risk was small enough that it could have occurred by chance. But there were strong trends toward significantly lower breast cancer risk for the women who ate the greatest amounts of vegetables and pulses (peas, beans and lentils) compared to women who ate the least amounts of these foods. All of the difference in risk between vegetarians and non-vegetarians could be accounted for by differences in vegetable and pulse intakes, even after taking into consideration the other known risk factors for breast cancer.

How big were the differences in the diets in the two groups? Women who ate the most vegetables and pulses (and had about half the incidence of breast cancer) ate more than 406 grams (about 8 cooked cups) of vegetables and 107 grams (about 3/4 cooked cup) of pulses a day. Women who ate the least vegetables and pulses (and had the highest incidence of breast cancer) ate less than 210 grams (about 2 cups) of vegetables and less than 35 grams (about 1/4 cup) of pulses a day.

What was the conclusion? The researchers concluded that higher consumption of vegetables and pulses by the vegetarian women may account for their lower rates of breast cancer, rather than differences in their consumption of meat.

What are the limitations of this study for western women? The East Asian vegetarians in this study had been lifelong vegetarians; many western vegetarians adopt vegetarian diets in adulthood. The amounts of vegetables and pulses eaten by the women in this study were much higher than those found in typical western diets, and the kinds of vegetables and pulses in the East Asian diet are different from those of the typical western diet. In addition, there may also be other lifestyle factors that make these women different from western women. For example, few of these women drank alcoholic beverages, a risk factor for breast cancer.

How do these results compare to those of other studies? These results are generally consistent with those of the few existing studies of vegetarians. Many case-control studies have reported similar protective effects of vegetable consumption on breast cancer risk. Several cohort studies have reported no protective effect of vegetable consumption on breast cancer risk, but some of these may have suffered from limited information on vegetable intake, especially the range and type of vegetables eaten in this study. Case-control studies collect dietary information after diagnosis and depend on memory. Cohort studies collect information before the disease occurs.

What are the take-home messages? First, vegetables and beans once again may have a protective effect on health. Second, read beyond the headlines, it wasn't being a vegetarian that was protective in this study, but eating more vegetables and beans. Third, when considering a study like this, consider how closely you, your diet, and your life style compare to the women in this study.

For more information go to: Dos Santos Silva I, Mangtani P, McCormack V, Bhakta D, Sevak L & McMichael, A. Lifelong vegetarianism and risk of breast cancer: a population-based case-control study among South Asian migrant women living in England. International Journal of Cancer 99(2002):238-244.

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Last Update 09.12.02