The relationship between dietary fats and breast cancer risk is complex. Most foods with significant fat levels contain a variety of fatty acids, including, in most cases, fatty acids that have been shown to increase breast cancer risk when studied in isolation. There is also evidence that the ratio of omega-6 to omega-3 fats in the diet is more important than the absolute amount of either fat. At the individual study level, this can present a confusing picture of the relationship between fat and breast cancer risk. However, a consensus concerning certain fats emerges when existing studies to date are considered as a whole.

Generally speaking, high-fat Western diets are associated with increased breast cancer risk, in part because they normally incorporates high levels of processed meat, butter and other animal fats, as well as fried foods, all of which have been associated with increased breast cancer risk. Saturated fats (found in red meat and dairy products) and trans fats (many commercial baked goods and certain margarines) have been found to promote breast cancer, although not all studies are in agreement. While omega-6 fats (corn oil, soybean oil, safflower oil) are essential to human health, they have also been shown to promote breast cancer. A relatively high omega-3 (fatty fish, walnut oil, flaxseed oil) intake can offset the potentially deleterious effects of omega-6 intake.

In fact, relatively high intakes of the marine fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are associated with reduced breast cancer risk and more favorable prognosis in women with early stage breast cancer. Olive oil (high in omega-9 fat) is associated with reduced breast cancer risk, especially HER2 overexpressing (HER2+) disease, despite the fact that one of its principal components, oleic acid, has been shown to promote breast cancer. This argues for consuming extra-virgin olive oil rather than highly refined olive oil that does not contain a significant fraction of the polyphenols that may contribute to olive oil's beneficial properties. Now a new study has reported that marine fatty acid consumption is associated with reduced breast cancer risk, whereas a variety of other fats appear to promote it.

Latest research examines breast cancer risk by type of fat consumed

The study referenced at the beginning of this news article was designed to investigate the associations between specific dietary fat intake and risk of breast cancer. The study included postmenopausal (age 50 to 76) members of the VITamins And Lifestyle (VITAL) Cohort. The women completed a food frequency questionnaire upon enrollment in 2000-2002. A total of 772 of the participants developed breast cancer during follow up.

Among polyunsaturated fatty acids (PUFAs), intakes of the marine fatty acids EPA and DHA were found to be associated with reduced breast cancer risk. Overall intake of monounsaturated fats (MUFAs) was associated with increased breast cancer risk women in the highest fifth of intake had 1.61 times the risk of breast cancer as those in the lowest quintile. High intake of the MUFAs myristoleic acid (biosynthesized from myristic acid, which is found in palm kernel oil, coconut oil, and butter fat) and erucic acid (mustard oil, rapeseed oil) conferred particularly high risk.

Overall intake of saturated fat appeared to be associated with increased risk of breast cancer (women in the highest fifth of intake had 1.47 times the risk), however this result barely reached statistical significance. High intake of the saturated fats (palmitic acid, palm oil, red meat, butter, lard), margaric acid (beef, lamb, high-fat dairy), and stearic acid (red meat, lard, butter) conferred significant high risk.

Total trans-fatty acid and polyunsaturated acid (a broad category of unsaturated fats that includes omega-3, omega-6 and omega-9 fatty acids) intakes were not associated with breast cancer. However, high intake of the trans-fatty acid linolelaidic acid (the trans fatty acid homolog of linoleic acid found in partially hydrogenated vegetable oils) was associated with increased risk. The authors conclude that different fats have different associations with postmenopausal breast cancer risk.

Note that while fatty fish such as salmon are recommended to protect against breast cancer and its recurrence, recent research suggests that fish oil supplements should not be used during chemotherapy.

Please see our article on recommended fatty fish for more information.