Being obese or overweight increases inflammation, insulin resistance and estrogen production, thereby increasing breast cancer risk and worsening breast cancer prognosis compared to normal weight. However, regular exercise or other physical activity can counteract these effects to some extent. In addition, consuming omega-3 fats has been found to be associated with reduced breast cancer risk in obese women. Now a new study has reported that omega-3 fats may act directly on tumor cells to inhibit proliferation and induce apoptosis (programmed cell death) rather than acting simply by reducing inflammation.

Sources of omega-3 fats

The best sources of omega-3 fats for breast cancer patients and survivors are found in fatty fish such as salmon, as well as walnuts and some oils:

Canola oil
Fish oil supplements
Flaxseed oil
Herring
Lake trout
Mackerel
Salmon, wild
Sardines
Walnuts
While fatty fish are recommended during treatment, recent research suggests that fish oil supplements should not be used by those undergoing chemotherapy.

Latest research finds omega-3 fats may act directly on breast cancer cells

The study referenced at the beginning of this news story was designed to investigate whether the reduction in breast cancer risk associated with intake of omega-3 polyunsaturated fatty acids is due to reduced obesity-associated inflammation and insulin resistance. To conduct the study, the authors used a mouse model of postmenopausal breast cancer: ovariectomized, immune-competent mice were injected with Py230 mammary tumor cells. Obesity was shown to increase inflammation in the mammary fat pad and promote mammary tumor formation. In fact, local inflammatory conditions were heightened in the mammary fat pad when tumor cells were present.

Tumor necrosis factor-alpha (TNF-α), which is involved in systemic inflammation, was the most highly upregulated cytokine in the obese mammary fat pad. Cytokines are small signaling molecules used in intercellular communication. (Inflammation involves the chronic activation of the immune system, resulting in the release of pro-inflammatory cytokines from immune system-related cells.) TNF-α was found to promote Py230 tumor cell growth in a dose-dependent manner. Mice fed a fish oil-enriched high-fat diet were found to have reduced inflammation in the obese mammary fat pad when there were no tumor cells present. In addition, the fish oil diet inhibited tumor growth.

The G-protein-coupled receptor 120 (GPR120) previously has been shown to mediate the anti-inflammatory and insulin-sensitizing effects of omega-3 fats. However, the fish oil diet was found to reduce tumor burden in a manner that did not require GPR120 in the host mouse. In fact, further experimentation showed that the omega-3 fats acted directly on the tumor cells to inhibit proliferation and induce programmed cell death. The authors conclude that obesity promotes mammary tumor progression and that omega-3 fats inhibit mammary tumor progression in obese mice independent of GPR120 in this animal model of postmenopausal breast cancer.

Please see our articles on inflammation, obesity and fatty fish for more information.