Too Much Omega-6, Not Enough Omega-3; Imbalance Linked to Increased Cancer Risk
WASHINGTON — Cancer experts said today that even though many Americans have cut back on fat, the relative amount of two specific kinds of fat in the typical diet remains â€œout of whackâ€� â€“ and unhealthy. Researchers at the American Institute for Cancer Research (AICR) expressed concern that American diets are overloaded with omega-6 fats and deficient in omega-3 fats, a state of affairs that has been linked to increased cancer risk.
Omega-6 fats are found in vegetable oils such as corn, safflower, sunflower and soybean oil. They are often used in processed snacks, baked products and commercial salad dressings.
Omega-3 fats are found mostly in fatty fish like salmon, sardines, trout and herring. Smaller amounts are found in canola oil, flaxseed, green leafy vegetables and walnuts. Omega-3 fats have displayed a range of anti-cancer activities in the laboratory and have been repeatedly associated with lower cancer risk in population studies.
Different Ratios = Different Risk
â€œThe ratio of omega-6s to omega-3s in the current American diet has been measured as high as 15:1,â€� said Melanie Polk, RD, Director of Nutrition Education at AICR. â€œTo put that figure in perspective, consider that according to the World Health Organization, in countries consuming a traditional plant-based diet, the ratio of omega-6s to omega-3s is closer to 4:1, or even 2:1.â€�
The ratio of â€œomegaâ€� fats in a given diet has been linked to heart disease for years, but new research suggests that it seems to have a direct effect on cancer risk, Polk said. â€œStudies that have compared the diets and disease rates of large populations show that when the â€œomegaâ€� fats are in better balance, the risk for breast cancer, prostate cancer and colon cancer is lower. The risk for heart disease and inflammatory conditions such as arthritis is also lower.â€�
But only recently have researchers uncovered a â€œsmoking gunâ€� that could explain how and why different ratios coincide with such striking differences in cancer risk.
Laboratory Reveals Possible â€œSmoking Gunâ€�
The key seems to be that both omega-6 fats and omega-3 fats are metabolized (processed) similarly by the body. Because their molecular structures are so similar, they compete for many of the same enzymes.
Once paired with an enzyme, however, omega-3s and omega-6s behave very differently. The molecules that arise when omega-3 fatty acids get metabolized provide a range of potential anti-cancer benefits. They show the ability to reduce the production of other, cancer-promoting enzymes, increase the rate at which cancer cells die, and help keep cancer cells from forming the new blood vessels needed for them to grow.
In fact, research funded by AICR has shown that adding omega-3 fatty acids to the diet of mice can actually reduce the occurrence of tumors and slow tumor growth. Dr. W. Elaine Hardman, Ph.D., a researcher at the Pennington Biomedical Research Center of Louisiana State University, has received several AICR grants to study the cancer-fighting potential of omega-3 fatty acids.
Her previous AICR-funded research has demonstrated that omega-3s also have a potential role in helping chemotherapy drugs work more effectively and in reducing side effects from cancer treatment. This July, Dr. Hardman will chair a panel devoted to the role of fat in the cancer process at the Annual AICR/WCRF International Research Conference on Food, Nutrition and Cancer taking place in Washington.
Another recently funded AICR grantee is investigating still another possible protective mechanism. Researchers Robert Chapkin, Ph.D. and Joanne Lupton, Ph.D. of Texas A & M University are investigating how a particular omega-3 fatty acid (docosahexaenoic acid, or DHA) interferes with a specific protein that is critical for tumor formation in the colon.
When omega-6 fatty acids pair with an enzyme, on the other hand, the resulting molecules can actually promote inflammation, spur cells to multiply, and decrease cancer cell death.
â€œOmega-6 fats do have a place in healthy diets,â€� said Polk. â€œThe problem right now is that 15:1 ratio. When the amount of omega-6 fat we consume is so hugely out of proportion with the amount of omega-3s in our diet, we effectively cut ourselves off from the protective benefits that omega-3s provide.â€�
Experts Advise Seeking Safe Dietary Sources of Omega-3s
Cold-water fish are the best dietary source of omega-3 fatty acids, but recent concerns about toxins in some fish have confused many people who are looking to get more omega-3s into their diet.
An article in the Summer 2004 issue of the AICR Newsletter helps individuals â€œfishâ€� for healthy omega-3 fats. Among its recommendations:
* Make sure to eat a variety of fish, but limit consumption of farmed salmon to two 3 oz. servings per week. Look for wild salmon, which is usually available frozen or canned.
* To reduce PCBs, remove skin and visible fat from fish. Bake, broil or grill fish instead of frying.
* Add plant foods that contain omega-3s to the diet. These include flaxseed and flaxseed oil, canola oil, walnuts, soybeans, wheat germ, green leafy vegetables such as spinach, kale, leeks and broccoli.
The AICR Newsletter also notes that although fish oil supplements can provide a hefty dose of omega-3s, they raise serious concerns for some people. Diabetics should note that fish oil supplements can affect blood sugar control. Individuals with bleeding disorders, and people taking blood-thinning medications such as aspirin, should not use fish oil supplements because they decrease the ability of the blood to clot. Cancer patients should get their doctorâ€™s approval before taking fish oil or any dietary supplement. Anyone who decides to take fish oil supplements should limit daily doses to 1000 mg.
The American Institute for Cancer Research (AICR) is the cancer charity that fosters research on diet and cancer and educates the public about the results. It has contributed more than $67 million for innovative research conducted at universities, hospitals and research centers across the country. AICR also provides a wide range of educational programs to help millions of Americans learn to make dietary changes for lower cancer risk. Its award-wining New American Plate program is presented in brochures, seminars and on its website, http://www.aicr.org. AICR is a member of the World Cancer Research Fund International.