Aggressive breast cancer is promoted by omega-6 fatty acids and slowed by omega-3 fatty acids

Omega-6 fatty acids, which are mainly found in seed oils, margarine, deep-fried foods, and industrially processed foods, are known to promote the growth of a particularly aggressive type of breast cancer. This was seen in a new study published in Science. Although omega-6 fatty acids are essential for life, many people consume far too much omega-6 through refined diets, and this contributes to the rising incidence of breast cancer and many other diseases. According to previous research, it is important for omega-6 fatty acids to be correctly balanced with omega-3 fatty intake, which can regulate the harmful activity in breast cancer cells. With this insight, researchers see new potential in the prevention and treatment of breast cancer.

Most breast cancers are hormone-sensitive, and about 13 percent of breast cancer types have a specific protein on the cell surface. These subtypes are called triple-positive (TPBC). About 15 percent of breast cancer cases are classified as triple-negative (TNBC) and represent the most aggressive subtype. The term triple-negative refers to the absence of three receptors, including estrogen receptors, that are often expressed in breast cancer cells and may respond to various therapies. After treatment, many patients with triple-negative breast cancer experience relapse within the first year, which results in a higher mortality rate.
Cancer arises when some cells in the body begin to divide uncontrollably. It often takes many years for tumors to become detectable, and the body’s natural mechanisms for combating abnormal cells are impaired. Usually, there is also an interplay between lifestyle, environmental, and hereditary factors, and diet plays a major role. Although there has been a lot of focus on carbohydrates, amino acids, vitamins, and minerals, research into fatty acids is somewhat limited.

Omega-6 fatty acids activate a specific signaling pathway that promotes cancer growth

Previous studies have shown that too much omega-6 may promote the onset of chronic inflammation and various types of cancer.
In the new study, researchers observed how the omega-6 fatty acid linoleic acid can activate a growth-promoting signaling pathway in tumor cells by binding to a protein called FABP5. When comparing breast cancer subtypes, they found that this signaling activation occurs in triple-negative breast cancer cells in particular, and these cells contain especially high levels of the FABP5 protein. In mouse models with triple-negative breast cancer, a diet high in omega-6 fatty acids also promoted tumor growth.
Earlier findings regarding the cancer-promoting effects of high omega-6 intake have been conflicting, nbut this study sheds new light on the mechanisms involved. It turns out that linoleic acid also activates a growth-promoting signaling pathway called mTORC1 in animal models with triple-negative breast cancer.
Because triple-negative breast cancer cells produce a substantial amount of the FABP5 protein, which activates the mTORC1 pathway, this may lead to increased cell growth. Indeed, mice with triple-negative breast cancer that were fed a high-omega-6 diet showed increased levels of FABP5, greater mTORC1 activation, and accelerated tumor growth.
Moreover, the researchers found that patients recently diagnosed with triple-negative breast cancer had elevated levels of FABP5 and linoleic acid in blood samples and tumor tissue.
The study is believed to be the first to demonstrate the mechanisms by which dietary omega-6 linoleic acid promotes malignant cell growth. The discovery of FABP5’s role in the process may also represent a new biomarker that can help guide breast cancer patients toward better treatment strategies.
Researchers are now looking into whether the omega-6/FABP5/mTORC1 signaling pathway affects other diseases, as it appears to promote the growth of prostate cancer cells as well. It is also possible that this pathway plays a role in other chronic conditions such as obesity and diabetes.

Why do so many people consume too much omega-6 and too little omega-3?

Omega-6 and omega-3 fatty acids must be obtained from the diet. Most of them are found in cell membranes, where they regulate numerous biochemical processes that affect inflammation, hormone balance, the nervous system, the circulatory system, cell growth, and much more. It is important to maintain a certain balance between these fatty acids so that processes function optimally.
However, with industrialization and the widespread fear of cholesterol, omega-6 fatty acids have become the most common type of fat in the Western diet. The primary sources are sunflower oil, grapeseed oil, corn oil, and other inexpensive vegetable oils, as well as margarine, fried foods, and processed foods, all of which contain the omega-6 form called linoleic acid.
Matters are only made worse by the fact that omega-3 intake from fatty fish and other sources has dropped drastically due to changing dietary habits and unnatural animal diets.
It is believed that the optimal omega-6 to omega-3 ratio is about 4:1. In modern diet, however, the ratio is typically around 20:1. This imbalance contributes to a wide range of metabolic disorders, chronic diseases, and cancer.
Therefore, it is advisable to reduce the intake of omega-6, especially from vegetable oils and processed foods, while still enjoying healthy sources such as nuts, seeds, and whole grains. Moreover, people should attempt to increase their intake of omega-3, especially from oily fish or fish oil supplements, to restore the proper balance between these two essential fatty acids.

A specific omega-3 fatty acid regulates harmful molecular activity in breast cancer cells

Omega-3 fatty acids exist in different forms. Plant sources such as flaxseed oil, rapeseed oil, and walnuts contain the ALA form. However, many people have difficulty converting this form into the active forms EPA and DHA, which are incorporated into cell membranes.
Since oily fish and fish oil supplements contain EPA and DHA, it is easier for most people to benefit from these omega-3 sources.
Previous studies have shown that EPA and DHA reduce the risk of breast cancer. Another study demonstrated that DHA inhibits the formation of various molecules involved in the development of the disease.

References:

Nikos Koundouros at al. Direct sensing of dietary ω-6 linoleic acid through FABP5-mTORC1 signaling. Science, 2025

Weill Cornell Medicine. Omega-6 fatty acids promote the growth of an aggressive type of breast cancer, study finds. ScienceDaily 2025

Sepideh Maralbashi et al. Docosahexaenoic acid (DHA) impairs hypoxia-induced cellular and exosomal overexpression of immune-checkpoints and immunomodulatory molecules in different subtypes of breast cancer cells. BMC Nutrition 2024

Dorota Dydjow-Bendek and Pawel Zagozdzon. Total Dietary, Fatty Acids, and omega-3/omega-6 Ratio as Risk Factors of Breast Cancer in the Polish Population – a Case-Control study. In Vivo January-February 2020