omega oils, diet and cancerFatty acids are essential to human health, but they’re not all created equal. While research is finding that omega-3 polyunsaturated fatty acids (PUFAs) can reduce cancer risk, omega-6 fatty acids appear to have the opposite effect, increasing the risk for disease, according to a review of research published in the May 12 issue of Cancer Letters.

In recent years, the balance of the Western diet has shifted considerably toward foods high in omega-6 fatty acids (animal fats, cereals, and vegetable oils), and away from healthier omega-3-rich foods (fish, nuts, and leafy vegetables). “Collectively, these dietary changes are thought to promote cardiovascular diseases, cancer, and inflammatory diseases,” says Isabelle M. Berquin, PhD, assistant professor in the Department of Cancer Biology at the Wake Forest University School of Medicine in Winston-Salem, North Carolina.

How might these fatty acids affect cancer development? When omega-6 PUFAs are broken down (metabolized) by enzymes in the body, they form inflammatory substances. Research is increasingly finding that inflammation plays a major role in cancer development. When omega-3 PUFAs are metabolized, they form substances that curb inflammation and may inhibit cancer development. These healthy fatty acids are also thought to interfere with cancer cells’ ability to grow and spread throughout the body.

Though research has been mixed on omega-3s and cancer protection, the benefit appears to be significant. “In some studies, cancer risk was reduced more than twofold for individuals consuming high amounts of omega-3 PUFAs,” Dr. Berquin says. So far researchers have found that omega-3 PUFAs may slow the growth and spread of colon, prostate, and breast cancers, and improve survival in patients with these diseases. Other types of cancer may also respond to these fatty acids, but this idea needs to be investigated further, Dr. Berquin says.

Research is also finding that nutritional supplements containing omega-3 fatty acids may help patients who already have cancer. Studies suggest that these supplements can reduce the weight loss, infections, and other unpleasant side effects of cancer treatment.

Though more research is needed to confirm whether omega-3 fatty acids can lower cancer risk, studies conducted so far provide compelling evidence that overall dietary changes can have real health benefits. “It is usually best to modify the diet to include a variety of food sources containing beneficial nutritional agents, because multiple agents modify cancer risk,” according to Dr. Berquin. “Reducing the overall fat consumption, eating a varied diet containing moderate amounts of fish and oils or nuts rich in omega-3 PUFAs, and taking good quality omega-3 supplements would be most beneficial.”

The healthiest forms of omega-3 fatty acids are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), found in cold-water fish such as mackerel, salmon, and tuna (just be wary of high mercury levels in tuna and king mackerel). Dark green leafy vegetables, flaxseed, and walnuts are also high in omega-3 fatty acids, but they may not protect against cancer as well as fish sources, Dr. Berquin says.

While increasing your intake of omega-3 fatty acids, it’s also a good idea to cut down on the less healthy omega-6 fatty acids by limiting the use of salad dressings and spreads, and avoiding fried and processed foods.

If you are interested in taking supplements or modifying your diet to increase the amount of healthy fatty acids it is recommended that you consult with your licensed healthcare provider.

Berquin IM, Edwards IJ, Chen YQ. Multi-targeted therapy of cancer by omega-3 fatty acids. Cancer Letters. 2008 May 12. [Epub ahead of print]

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