In studies with rats, pregnant rats fed diets high in omega-6 have increased estrogen levels and later female offspring had an increased incidence of breast tumors. Rats fed diets in omega-3 have the opposite result, with a decreased risk for breast cancer in female offspring.
Infants who are breast fed have been shown to have a reduced risk of developing breast cancer before menopause of up to 35%. This may be due to the presence of DHA in breast milk, although maternal dietary intake determines the DHA content. It has been noted that maternal intake of trans fatty acids may reduce the DHA content.
Pre-puberty and Puberty
Diets fed to rats high in omega-6 prior to puberty had a higher incidence in breast tumors, compared to rats only fed high omega-6 diets post puberty. A low fat diet high in omega-3 reduced incidence of breast cancer, but a high fat high omega-3 diet resulted in increased incidence.
There are limited studies in humans, but it is noted that Asian women have a low rate of breast cancer. Diets of Asian women are typically higher in omega-3 PUFA content and also higher intake of foods with EPA and DHA. In North Americans, diets are higher in omega-6 and omega-3 intake is primarily from ALA. Asian women who immigrate to the United States develop breast cancer at the same rate as Americans within a generation, and obesity rates increase twofold between the first and second US generations, with changes in dietary and other environmental and lifestyle changes. Further studies with humans are needed to examine the relationship between fatty acids and breast cancer in humans.
Food sources of saturated fat: butter, whole fat dairy products, fatty meats, coconut and palm oils.
Food sources of monounsaturated fats: olive oil, peanut oil, avocados, nuts (oleic fatty acid-olives and olive oil). Food sources of trans-fatty acids: margarine, high fat baked goods and crackers, fried fast foods.
MacLennan and Ma Breast Cancer Research 2010, 12: 2011 (http://breast-cancer-research.com/content/12/5/211