Breast cancer is the most common cancer in women globally. Many studies have shown the influence of diet on cancer. Although no food can completely prevent breast cancer, certain foods can certainly help lower the risk of breast cancer or reduce breast cancer growth rate.

Incidence of breast cancer in relation to fat intake

Although the relationship between dietary fat intake and breast cancer is contentious, many epidemiological studies suggest that the association between dietary fat and breast cancer may be a result of the type of fat intake rather than the total fat intake. Studies have shown that there is a significant difference in the incidence of breast cancer between western and Asian populations. This difference may be attributable to a lack of fish consumption in a typical western diet rich in omega-6 polyunsaturated fatty acids (PUFA) that are known to be pro-inflammatory.

A diet containing fish, on the other hand, is rich in omega-3 fatty acids that are helpful in reducing inflammation. Therefore, the ratio of omega-3 and omega-6 fatty acids in the diet regulates the inflammatory status of the body that can, in turn, influence breast cancer growth rate and spread.

Long-chain omega-3 fatty acids are not synthesized by the body

Fish oil supplements contain long chain omega-3 fatty acids that are not synthesized by the body and must be obtained from the diet. The role of these omega-3 fatty acids in changing the microenvironment of the breast tumor and in the regulation of metastasis is an important determinant of the ability of fish oil supplements to reduce breast cancer growth rate.

Study analyzes the effects of omega-3 and omega-6 PUFA on breast cancer

A recent study published in the journal Clinical & Experimental Metastasis analyzed the effects of long chain omega-3 fatty acids on breast cancer growth rates and metastasis to different organs including bone, heart, kidneys, ovaries and contralateral mammary glands.

The researchers at the University of Nebraska Medical Center, USA, conducted the study on 40adult female mice. The mice were divided into two groups and both the groups were fed a liquid diet containing the same calorie count and fat percentage. The only difference in their diets was one group was fed plant oils rich in omega-6 polyunsaturated fatty acids while the other group’s diet contained fish oil rich in long-chain omega-3 polyunsaturated fatty acids.

After 16 weeks of following this diet, 4T1 breast cancer cells were injected into both the mice groups. 4T1 breast cancer cells cause the formation of aggressive breast tumors that spread to the preferential metastatic sites such as lungs and liver. After 35 days of breast cancer cells injection, the researchers performed an autopsy on the mice in both groups.

Reduced breast cancer growth rate in mice fed Omega-3 fatty acid diet

The researchers observed that it took much longer for breast cancer tumor to develop in the mice on the omega-3 diet as compared to mice that were fed omega-6 diet. Furthermore, because of slower breast cancer growth in omega-3 fed mice, the size of the tumor was 50% smaller and the spread of cancer cells to both preferential and other organs was much lower as compared to omega-6 fed mice.

The researchers observed that the mice fed omega-3 diet survived longer than the mice fed omega-6 diets. Notably, two mice in the omega-3 diet group did not develop breast cancer at all.

How do omega-3 fatty acids slow breast cancer growth rate?

T-cells are an important type of white blood cells that play a large role in the immune system. They are especially important in cell-mediated immunity which is the primary defense against cancer.

In this study, the researchers found a much higher number of T cells in the autopsied tissues of the mice that were fed omega-3 diet than in the mice fed omega-6 diet. In addition, there was less inflammation observed in mice in the omega-3 group. The analysis of tumor tissues showed a lower formation of new blood vessels in the tumor, higher tumor cell death, and increased Interleukin 10, an anti-inflammatory cytokine, in the omega-3 fed mice compared with omega-6 fed mice. These changes indicate that omega-3 fatty acids play an important role in reducing breast cancer growth rate.

Does omega-3 rich diet prevent breast cancer?

This study highlights the beneficial effects of consuming long-chain omega-3 fatty acids. A diet rich in foods containing omega-3 fatty acids, such as fish oil, helps to suppress inflammation and promote T-cell immunity against tumors thereby reducing development and spread of breast cancer.

The researchers, however, caution that omega-3 rich diet can suppress or delay the development of breast cancer but may not totally prevent it. In addition, since these studies were carried out with one strain of mice and one type of tumor cells, the researchers suggest the need for future studies to validate the generalizability of these results.

Include long-chain omega-3 fatty acids in diet

This study clearly concludes that a diet rich in omega-3 polyunsaturated fatty acids reduces breast cancer growth resulting in reduced frequency and number of metastatic sites thus prolonging the survival of mice.

Although more studies are needed to conclude that fish oil reduces the risk of breast cancer, the addition of omega-3 rich foods such as salmon, mackerel, and anchovies diet may be beneficial in reducing breast cancer growth rate.

Written by Preeti Paul, MS Biochemistry

Reference: Saraswoti Khadge et al., Long-chain omega-3 polyunsaturated fatty acids decrease mammary tumor growth, multiorgan metastasis and enhance survival. Clinical & Experimental Metastasis. https://doi.org/10.1007/s10585-018-9941-7