Recent laboratory findings and the results of a new population study support the hypothesis that the long-chain “marine” omega-3s found only in fish are very promising food factors for prevention of breast cancer.
But new research also indicates that timing may play a key role: a factor that appears to apply to soy's cancer-preventive powers as well.
In both cases—soy and marine omega-3s—it appears that these dietary factors offer more preventive potential when women begin consuming them before puberty and continue consuming them throughout their lives.
Omega-3s versus breast cancer: timing and fat intake seen as key
Let’s summarize the findings of recent research, which clarify the potential of omega-3s to prevent breast cancer (key findings in italics).
New clinical study: omega-3s at puberty reduce breast cancer risk
Research presented at the American Institute for Cancer Research’s July, 2005 conference on diet and cancer showed that omega-3 fats, when part of an overall low-fat pre-puberty diet, reduced growth of the breast cells most likely to develop cancer and increased the activity of genes responsible for DNA repair. While a low-fat diet rich in omega-3s was linked with less DNA damage, girls who consumed a high-fat diet and the same amount of omega-3 fat experienced greater DNA damage.
Interestingly, these results match those seen in one of the animal studies described below (see Study #1).
New population study: omega-3s reduce breast cancer risk
In September of this year, Japanese researchers published the results of a study designed to find any association between various dietary fatty acids and breast cancer risk. From 1988 to 1990, 26,291 women aged 40-79 participated in the Japan Collaborative Cohort (JACC) Study.
The women completed a questionnaire on dietary and other factors. The researchers analyzed the women’s health status seven years later, and found that the 25 percent of women who ate the most marine omega-3s (mostly in fish) enjoyed a significant decrease in risk, compared with the 25 percent of women who ate the least.
In contrast, women who ate the most omega-6 vegetable fat had more than twice the risk. They found no clear association between total fat intake and breast cancer risks.
As the researchers said, “This prospective study did not support any increase in the risk of breast cancer associated with total or saturated fat intake, but it suggested the protective effects of the long-chain n-3 fatty acids that are abundant in fish.”
New animal studies: omega-3s work best when total fat intake is low
Earlier this year, researchers at Georgetown University’s Lombardi Comprehensive Cancer Center published the intriguing results of two animal studies designed to tease out the effect of omega-3s and soy on breast cancer risks.
STUDY 1: Researchers at Georgetown University’s Lombardi Comprehensive Cancer Center found that rats fed a low-fat diet rich in omega-3s enjoyed a reduced risk of mammary tumors. In contrast, rats fed high-fat diets rich in omega-3s suffered an increased risk of breast cancer.
STUDY 2: Asian women have lower breast cancer risk than Caucasian women eating typical Western diets. However, they have higher average estrogen levels at pregnancy—a known risk factor for breast cancer—compared with Caucasian women. Researchers at Georgetown University set out to test the effects of three different maternal diets—one high in omega-3s, one high in omega-6s, and one high in genistein from soy—on the risk of breast cancer in rat offspring.
The female offspring of rats fed a diet rich in omega-3s had a reduced risk of mammary tumors, compared with the children of rats fed diets high in omega-6 fatty acids or genistein from soy.
As the researchers concluded, “Our findings indicate that the elevated estrogen levels in the… mothers [fed a diet rich in omega-3s] were linked to reduced rather than increased breast cancer risk among their offspring, suggesting that other effects of n-3 PUFA [omega-3s] may counteract the effects of high fetal estrogenicity on the mammary gland. High maternal genistein intake did not reduce offspring’s breast cancer risk, and therefore high maternal soy intake in Asian women may not be associated with daughters’ low breast cancer risk.”
STUDY 3: At a July, 2005 diet-cancer conference, Coral A. Lamartiniere, Ph.D. of the University of Alabama at Birmingham presented the results of a study titled “Genistein chemoprevention of breast cancer: timing and mechanisms of action”. Her results indicate that genistein from soy offers no protection from breast cancer when it is first given to animals in adulthood. But when the animals ate it before puberty, they had less breast cancer development, and the benefits were even greater when they continued to eat it into adulthood. It appears that eating soy just before and during puberty creates permanent cancer-protective cellular pathways.
Omega-3s and risk reduction: eat fish early and forever
It seems that to maximize risk reduction, women should start eating a relatively low-fat diet rich in fish before puberty, and continue the habit throughout life.
The findings we've summarized above also suggest that women should get most of their dietary fat from fish, and cut back on the omega-6 fats concentrated in processed foods and in common cooking oils like corn, sunflower, and safflower. Note: You should not cut back too severely, as the body needs about a 2:1 or 3:1 ratio of dietary omega-6 to omega-3 fatty acids for basic health.
Oils rich in monounsaturated fats—olive and macadamia—are not associated with increased breast cancer risk, but and appear to help protect heart health.
Soy and breast cancer: timing is key
For many years now, women have been told to eat soy foods to help prevent breast cancer, based on the assumption that high soy intake among Asian women may explain why they have a lower risk of breast cancer than American women.
However, animal tests fail to confirm this hypothesis, and some indicate that the phyto-estrogens in soy—primarily genistein—actually increase the growth of breast cancer cells.
New laboratory studies indicate that with soy, timing is a critical factor. In a study of Chinese women, those who reported consuming three or four servings of soy foods a week as teenagers were half as likely to develop breast cancer as those who rarely ate soy foods. Soy consumption as adults had no effect on the women's breast cancer risk in this study.
In another investigation, Asian-American women who ate soy even once a week during adolescence reduced their risk of breast cancer later. In this study, regular consumption of soy foods during adolescence lowered their breast cancer risk even if they did not eat it regularly later in life, but the women who continued eating soy as adults had the lowest risk.
· Adlercreutz H. Phytoestrogens and breast cancer. J Steroid Biochem Mol Biol. 2002 Dec;83(1-5):113-8. Review.
· Binukumar B, Mathew A. Dietary fat and risk of breast cancer. World J Surg Oncol. 2005 Jul 18;3:45.
· Cotroneo MS, Wang J, Fritz WA, Eltoum IE, Lamartiniere CA. Genistein action in the prepubertal mammary gland in a chemoprevention model. Carcinogenesis. 2002 Sep;23(9):1467-74.
· Dai Q, Shu XO, Jin F, Potter JD, Kushi LH, Teas J, Gao YT, Zheng W. Population-based case-control study of soyfood intake and breast cancer risk in Shanghai. Br J Cancer. 2001 Aug 3;85(3):372-8.
· Hilakivi-Clarke L, Cho E, Cabanes A, DeAssis S, Olivo S, Helferich W, Lippman ME, Clarke R. Dietary modulation of pregnancy estrogen levels and breast cancer risk among female rat offspring. Clin Cancer Res. 2002 Nov;8(11):3601-10.
· Hilakivi-Clarke L. Early life exposure to n-3 polyunsaturated fatty acids, breast cancer risk and the mediating pathways. Georgetown University Lombardi Comprehensive Cancer Center Washington, DC, USA. 2005 WCRF / AICR International Research Conference on Food, Nutrition and Cancer, July 14-15, Washington, D.C.
· Jakes RW, Duffy SW, Ng FC, Gao F, Ng EH, Seow A, Lee HP, Yu MC. Mammographic parenchymal patterns and self-reported soy intake in Singapore Chinese women. Cancer Epidemiol Biomarkers Prev. 2002 Jul;11(7):608-13.
· Lamartiniere CA. Genistein chemoprevention of breast cancer: timing and mechanisms of action. University of Alabama at Birmingham, Birmingham, AL, USA. 2005 WCRF / AICR International Research Conference on Food, Nutrition and Cancer, July 14-15, Washington, D.C.
· Olivo SE, Hilakivi-Clarke L. Opposing effects of prepubertal low- and high-fat n-3 polyunsaturated fatty acid diets on rat mammary tumorigenesis. Carcinogenesis. 2005 Sep;26(9):1563-72. Epub 2005 May 11.