Ask the Expert: Breast Cancer

The Physicians Committee

Ask the Expert: Breast Cancer

Q: For an overweight breast cancer survivor, is it important to just focus on eating healthy foods, or is weight loss important too?

A: You’ll want to focus on both. Evidence suggests you can improve your chances of surviving breast cancer and reduce recurrence by achieving a healthy weight post-treatment. The best way to lose weight is to choose healthy, low-fat meals built from legumes, grains, vegetables, and fruit, and to incorporate moderate physical activity into your lifestyle. Of course, it’s important to check with your doctor to understand the type and level of exercise appropriate for you.

Chlebowski RT, Blackburn GL, Thompson CA, et al. Dietary fat reduction and breast cancer outcome: interim efficacy results in from the Women’s Intervention Nutrition Study (WINS). J Natl Cancer Inst. 2006; 98(24):1767-1776.

Pierce JP, Stefanick ML, Flatt SW, et al. Greater Survival after breast cancer in physically active women with high vegetable-fruit intake regardless of obesity. J Clin Onc. 2007;25(17):2345-2351.

Q:  How important is diet for young girls in families with a history of breast cancer?

A:  The foods girls eat while in pre-school and grade school appear to have an important effect on breast cancer risk later in life. Researchers at Harvard have discovered that girls who eat more protein from animal sources and less protein from plant sources tended to reach their first menstruation earlier. Younger age at first menstruation is connected with increased risk of breast cancer later in life.

Frazier AL, Ryan CT, Rockett H, Willett WC, Colditz GA. Adolescent diet and risk of breast cancer. Breast Cancer Res. 2003;5(3):R59-64.

Stoll BA. Western diet, early puberty, and breast cancer risk. Breast Cancer Res Treat. 1998;49(3):187-193.

Q: My mother was diagnosed with breast cancer at age 55. After hearing that soymilk contains breast cancer-fighting isoflavones and phytoestrogens, I stopped drinking cow's milk and started drinking soymilk instead. But, lately, I've heard that the estrogen in soymilk INCREASES your risk for breast cancer. Which is it? Is soy good or bad?

A: In Asia, where tofu and other soy products are commonly consumed, cancer and heart disease are much more rare than in the United States and Europe, and longevity is greater. Because these geographic areas differ in many other ways—Asians also eat much less meat and dairy products and generally exercise more, but also smoke more cigarettes and eat more salt—researchers have attempted to tease out the effects of soy itself.

Soy products have been shown to lower serum cholesterol levels, in part due to their rich content of soluble fiber. They also reduce estrogen activity, at least in premenopausal women, which, over the long run, reduces cancer risk. The evidence is not as clear for postmenopausal women.

Like all foods, soy has its advantages and disadvantages. Soybeans are rich in essential omega-3 fatty acids, but tend to be higher in total fat than other beans. Many soy products derive roughly half their calories from fat, while black beans, pinto beans, or other varieties are only about 4 percent fat. Also, soy extracts, such as genistein, may not have the same beneficial effects as products made with the whole bean.

Soy products make convenient and tasty substitutes for meat and other unhealthy foods that people, quite rightly, are looking to avoid. However, a varied, low-fat, plant-based diet centered around beans, vegetables, grains, and fruits does not necessarily have to include soy products to be nutritionally complete. The benefits of complete protein and soluble fiber can easily be found in other beans, vegetables, grains, and fruits as well.

Brzezinski A, Debi A. Phytoestrogens: the "natural" selective estrogen receptor modulators? Eur J Obstet Gynecol Reprod Biol. 1999;85:47-51.

Kurzer MS. Hormonal effects of soy in premenopausal women and men. J Nutr. 2002;132:570S-3S.

Cui X et al. Dietary patterns and breast cancer risk in the shanghai breast cancer study. Cancer Epidemiol Biomarkers Prev. 2007;16(7):1443-1448.

Q: I’ve read that milk consumption decreases risk for breast cancer in premenopausal women. How could this be if milk consumption increases a woman’s level of IGF-1 and may increase breast cancer risk after menopause?

A: A study in Norway in 2001 created a stir, because it concluded that milk consumption reduces breast cancer risk in premenopausal women. But breast cancer is quite uncommon in premenopausal women (only 0.6 percent in this study). Also, the study relied solely on self-reported milk intake during adulthood and the recollection of milk intake during childhood, not on key blood markers related to breast cancer risk or overall dairy product intake.

The nutrient that is hypothesized to be protective is conjugated linoleic acid (CLA), a component of dairy fat; however, CLA has been shown to increase risk for heart disease. A number of other studies have shown either no association between breast cancer incidence and dairy product consumption or an increase between the two. Research has shown that foods influence breast cancer development by their actions on circulating hormone levels (especially estrogen). Fatty foods increase estrogen levels while high-fiber foods naturally decrease them. High-fat diets also fuel obesity, which is associated with elevated estrogen and increased breast cancer risk.

In Asia, where whole grains, vegetables, fruits, tofu, soymilk, and other soy products are commonly consumed and milk is not a normal part of the diet, people are generally healthier and breast cancer is much rarer than in the United States and Europe.

Hjartaker A, Laake P, Lund E. Childhood and adult milk consumption and risk of premenopausal breast cancer in a cohort of 48,844 women - the Norwegian women and cancer study. Int J Cancer. 2001;93(6):888-893.

Hankinson SE, Willett WC, Colditz GA, et al. Circulating concentrations of insulin-like growth factor I and risk of breast cancer. Lancet. 1998;351:1393-1396.