The Link Between Diet and Breast Cancer

The Link Between Diet and Breast Cancer

Diet can have an effect on a woman's risk for breast cancer. How do factors such as calories, alcohol, and soy play a role?

Smart nutrition and a diet that keeps you at a healthy weight can help reduce your risk of breast cancer, the most common cancer diagnosis among American women.

Diet and Breast Cancer: Increased Risk With Weight Gain

Among post-menopausal women, the age group most susceptible to breast cancer, the evidence continues to implicate weight gain as a risk factor for breast cancer. In one recent study, obese women in their post-childbearing years had a 3.2 times greater chance of breast cancer than women of a healthy weight. The researchers took into account several other factors that affect breast cancer risk, including a woman’s age, age at menopause, family history of breast cancer, and history of childbearing.

Among breast cancer survivors, researchers are beginning to associate excess weight with an increased risk of recurrence and mortality, says Colleen Doyle, MS, RD, director of nutrition and physical activity for the American Cancer Society.

It’s tempting to think that a low-fat or vegetable-filled diet would reduce breast cancer, but the association between these diets and breast cancer prevention really hasn’t panned out, Doyle explains. In one study that showed a connection between a low-fat diet and reduced risk of breast cancer recurrence, the study participants also lost weight. “So it wasn’t really clear — is it effect from low fat or weight loss? I tend to think it’s probably weight loss because dietary fats have been discounted as a prevention factor for breast cancer,” Doyle says.

Diet and Breast Cancer: The Effect of Eating Soy

For promoting general good health, nutritionists like to recommend soy-based foods. They are high in protein and their low-fat content earns them a spot in a weight-control regimen. In and of themselves, however, soy foods do not appear to help reduce cancer in general or breast cancer specifically.

“Tofu certainly fits within our message to eat a plant-based diet,” Doyle says, “but there’s really no good evidence soy reduces breast cancer risk. However, there are plenty of other reasons to eat soy. Soy is packed with phytochemicals and antioxidants, which are beneficial for health.”

Soy contains a very weak plant-based estrogen, raising the question of whether soy-based foods could fuel hormone-related cancers such as breast cancer. The issue is of particular concern to breast cancer survivors. “Our recommendation is that it’s likely safe for breast cancer survivors to eat soy in amounts typical of the moderate Asian diet, which is no more than three servings of soy products a day,” says Doyle.

While that sounds like a lot of soy, it’s might be just a soy drink in the morning, some miso soup at lunch, and tofu at dinner, points out Shayna Komar, RD, LD, a dietitian with Cancer Wellness at Piedmont in Atlanta.

Moderate levels of food sources of soy appear to pose no risk of breast cancer, but nutritionists caution against the use of powdered soy and similar supplements. The level of plant estrogens in such products is unknown and may exceed safe levels, Doyle says.

Diet and Breast Cancer: Alcohol and Increased Risk

Alcohol seems to increase the risk of breast cancer, particularly if a woman has low levels of folate, the water-soluble B vitamin found in leafy green vegetables and beans. For now, the American 

Cancer Society recommends women consume no more than one glass of alcohol per day, but Doyle points out that even two drinks per week might increase a woman’s breast cancer risk.

The uncertainty arises, Doyle says, from the structure of studies on the relationship between alcohol and breast cancer risk. Most studies examining the effect of alcohol consumption start at one glass per day, and do not capture effects that may begin at levels lower than that.

Complicating the picture is the fact that moderate use of alcohol has been established to lower the risk of heart disease, the leading cause of mortality among women in the United States. “The message for women about alcohol and breast cancer prevention is that it’s important to look at your risk of breast cancer and heart disease and make an informed decision about whether you drink at all. If you don’t drink, there’s no reason to start,” Doyle says. "There are a lot of healthier ways to reduce your risk of heart disease."