Nutrition and Breast Cancer

Breast cancer remains the No. 2 cause for cancer-related deaths in women, despite advances in treatment and early detection that have led to a reduction in overall breast-cancer mortality since the early 1990s. Consequently, identification of lifestyle choices that can prevent breast cancer and its recurrence remains a high research priority.

The recently updated Guidelines on Nutrition and Physical Activity for Cancer Prevention (CA: A Cancer Journal for Clinicians, 2006; 56:254-281) from the American Cancer Society emphasizes the holy trinity of cancer prevention: a healthy weight, physical activity and good diet.

Weight and dietary fat

The strongest link between weight and breast-cancer risk appears to relate to increased estrogen production from adipose tissue, especially for postmenopausal women, who are most susceptible to estrogen-receptor- positive breast cancer. Recent research from The Nurses Health Study, reported in the Journal of the American Medical Association (2006; 296(2):193-201), showed that gaining 55 lbs. after the age of 18 increased breast-cancer risk by 45%, and losing 22 lbs. after menopause reduced risk by 23%. For cancer survivors, the risk of recurrence increases if they are overweight at the time of diagnosis, or gain weight during and after treatment.

Other observations indicate that metabolic conditions often associated with excess weight, such as high levels of insulin, insulin-like growth factors (IGFs) and blood glucose, may play a role in cancer development. Since increased circulating fatty acids accompany the energy imbalance of obesity, researchers question the role of fatty acids in the production of IGFs as a mechanism for obesity to raise cancer risk. Now research sponsored by the American Institute for Cancer Research, Washington, D.C., aims to examine the effect of palmitate and oleate on the production and activity of IGFs in malignant and healthy breast cells. The virtues of a low-fat diet in breast-cancer prevention remain unclear. In 2005, at the American Society of Clinical Oncology (ASCO) meeting, researchers from the Womens Intervention Nutrition Study reported that a low-fat diet may reduce recurrence of breast cancer in postmenopausal women with estrogen-receptor-negative cancer. In 2006, results from The Womens Health Initiative (WHI), an eight-year randomized study of postmenopausal women, showed that a low-fat diet with higher fruit, vegetable and grain intake did not significantly lower breast-cancer risk, compared to a regular diet (Journal of the American Medical Association, 2006; 295(6):629-642). However, results suggest that those eating a higher-fat diet initially benefited by switching to a low-fat diet and that a longer follow-up may show different results.

Several confounding variables limit the interpretation of these and similar studies. To begin with, other dietary and nutritional factors may impact cancer risk change when one follows a low-fat diet. Usually, fruit, vegetable and grain consumption increases and red meat consumption decreases. Frequently, total caloric intake drops and weight loss ensues. Perhaps in the end, the value of a low-fat diet may lie in its role as a weight reduction and management tool.

The food factor

Studies on the impact of specific foods on breast-cancer risk present mixed results, as well. A study on meat, egg and fish consumption during midlife and later reported no link with breast-cancer risk (International Journal of Cancer, 2003; 104(2):221-227), contrary to earlier reports of reduced risk with fish and increased risk from red meat and eggs. A meta-analysis on soy intake and breast-cancer risk (Journal of the National Cancer Institute, 2006; 98(7):459-471) indicated that soy intake may reduce breast-cancer risk but did not address soy consumption by survivors, soy supplements or the influence of soy consumption at different stages of life. Thus, the question of soys weak estrogenic effect remains unanswered.

The European Prospective Investigation Study into Cancer and Nutrition (EPIC) looked at fruit and vegetable consumption and breast cancer risk for participants and, like an earlier pooled analysis of eight cohort studies, found no association (Journal of the American Medical Association, 2005; 293(2):183- 193). However, a large case-control study from Italy examined flavonoids and showed an inverse relationship between breast-cancer risk and flavones. The authors believe the results might partially explain an inverse relationship between vegetable consumption and breast-cancer risk in Mediterranean populations (Cancer Epidemiology Biomarkers & Prevention, 2005; 14(4):805-808).

Beyond food groups

While some investigations suggest that specific nutrients may influence breast-cancer development, no nutrient or dietary component stands out as a magic bullet for prevention. A higher folate intake appears to reduce the risk of developing estrogen-receptor-negative breast cancer, particularly in women who consume alcohol, but not estrogen-receptor-positive cancer (Cancer Epidemiology Biomarkers & Prevention, 2005; 14(8):2,004- 2,008). Some studies suggest a protective effect from vitamin D and calcium supplements. But a randomized trial from the WHI cohort (reported at the ASCO Annual Meeting, 2006, Abstract LBA6) found no connection between calcium and vitamin D supplements and reduced breast-cancer risk in postmenopausal women.

However, some dietary components may help combat cancer during treatment. Flaxseed lignan may reduce tumor growth in patients with breast cancer, according to one small study (Clinical Cancer Research, 2005; 11:3,828-3,835). Preclinical studies on a yeast beta-glucan from Biopolymer Engineering, Inc., Eagan, MN, demonstrated increased tumor regression when administered to mice in combination with the drug Herceptin®. And studies on a purified blackberry compound, cyanidin-3-glucoside, inhibited tumor growth and spread when used as a supplement for mice with skin tumors and lung cancer (Journal of Biological Chemistry, 2006; 281(25):17,359- 17,368). Conceivably, future prescriptions for breast cancer may include foods or dietary supplements that enhance and complement other therapies. 

Angela M. Miraglio, M.S., R.D., is a Fellow of the American Dietetic Association from Des Plaines, IL. Her firm, AMM Food & Nutrition Consulting, provides communications and technical support to the food and beverage industry. She can be reached at [email protected].