Holmes DH, et al.
International Journal of Cancer, January 9, 2003

Background and importance of the study: The risk of developing breast cancer is very different from country to country. So are people's diets. This is one reason researchers have long suspected that diet may affect breast cancer risk. A few small studies have suggested that a diet high in meat or eggs might increase breast cancer risk. Other studies have found that a diet high in fish or seafood may lower the risk.

This study looked at how eating meat, fish, and eggs was related to women's risk of developing breast cancer. The study also looked at whether different ways of cooking meat might affect breast cancer risk.

Study design: The researchers used questionnaires to keep track of the diet and breast cancer rates of more than 85,000 women in the United States. These women ranged in age from 30 to 55 at the start of the study.

Over the 18 years of the study, the women received five diet questionnaires. Of the 88,647 women who answered them, 4,107 (4.6%) developed invasive breast cancer. The researchers compared the diets and cooking habits of women who developed invasive breast cancer with the diets and cooking habits of those who did not.

In their calculations, the researchers compared women who were similar in terms of many of the factors that can influence breast cancer risk, including:

• age
• alcohol intake
• age at first birth
• body mass index at age 18
• weight change since age 18
• personal history of breast cancer
• family history of breast cancer
• menopausal status
• past and present use of hormone replacement therapy

Results and conclusions: The researchers found no link between breast cancer risk and a diet high in fish or red meat (hamburger, beef, pork, or lamb) during mid-life and later. They also found no evidence that how red meat was cooked affected breast cancer risk. The risk was nearly the same for women who ate well-cooked, rare, or charred meat (from barbecuing). Even women with a family history of breast cancer were at no higher risk of developing the disease if they had a diet high in meat or low in fish. Women who ate one or more eggs a day had a breast cancer risk that was slightly, but not significantly, higher than those who ate eggs less often.

Take-home message: This study did not look at how diet early in life affects breast cancer risk. But it did look at a very large number of women to see how meat, fish, and eggs in the diet from age 30 on might affect their risk for the disease.

Because it included so many women and was conducted in a relatively consistent fashion over so many years, this study is probably more reliable than previous studies that linked diets high in meat or low in fish to breast cancer risk.

Still, studies like this are difficult by nature because people don't always remember or report correctly on what they've eaten over the years. And it's very hard to look only at links between diet and breast cancer, because so many other factors might also affect the risk. For example, what if women who eat a lot of red meat also exercise more than women who eat less red meat? In this case, the exercise might help balance any possible increased risk associated with red meat.

Keeping in mind these limitations, this study still provides some new insights on meat, fish, eggs and breast cancer risk. It suggests that eating red meat and eggs—as a single factor—may not increase your risk of breast cancer.

But this doesn't mean that eating lots of red meat and eggs is good for you, or that you shouldn't try to include more fish in your diet. A diet high in fruits, vegetables, fiber, and low-fat foods, and low in fat and cholesterol, has been shown to improve weight control and lower the risk of heart disease. And it might be your best bet for maintaining optimal health, energy, and quality of life.