American Institute for Cancer Research
Newsletter 84, Summer 2004
How Omega-3 Fats May Protect against Cancer
A growing body of research suggests that omega-3 fatty acids may reduce cancer risk and help manage certain cancers. For good health, Americans need to eat more omega-3 and fewer omega-6 fatty acids.
Cancer scientists continue to find cancer-fight- ing potential in omega-3 fatty acids. Omega-3s are a type of polyunsaturated fat, found mainly in fatty fish like salmon, and to a lesser extent in certain vegetables, nuts, seeds and oils. Human and laboratory studies show evidence that omega-3s may lower cancer risk.
"Populations in countries that consume high amounts of omega-3 fatty acids from fish have lower incidences of breast, prostate and colon cancer than people in countries that consume less omega-3s," explains W. Elaine Hardman, Ph.D., a researcher at the Pennington Biomedical Research Center of Louisiana State University. In laboratory studies funded by AICR, Hardman has found that supplementing the diet with omega-3s can reduce occurrence of tumors.
Omega-3s may also help cancer therapy's effectiveness. In other laboratory studies, Dr. Hardman found that adding fish oil to the diet can slow tumor growth, help chemotherapy drugs work more effectively and reduce side effects from cancer treatment.How Omega-3s Work
Many mechanisms are thought to be responsible for the ability of omega-3s to fight cancer. For example, they may reduce the production of enzymes that promote cancer cell growth, increase the rate of cancer cell death and suppress the formation of new blood vessels required for cancer cells to grow.
Supported by a grant from AICR, researchers Robert Chapkin, Ph.D., and Joanne Lupton, Ph.D., of Texas A & M University, are investigating the mechanisms by which DHA (docosahexaenoic acid), the major omega-3 fatty acid in fish oil, alters colon cell function in mice and rats. A type of protein called Ras plays a critical role in tumor formation in the colon. For this protein to function and drive the cancer process, it needs to reach a specific destination within the cell.
"We found that DHA interfered with the ability of the protein to get where it needs to go in the cell," says Dr. Chapkin. "Altering the migration patterns of protein within cells may reduce the risk of developing colon cancer." This research adds to other evidence suggesting omega-3s may reduce colon cancer risk and tumor growth.Fat Ratio Is Important
It's not only important to consume enough omega-3s, but also to get a healthy balance with other fats in the diet. Both laboratory and human studies suggest that the ratio of omega-6 to omega-3 fatty acids is important to reducing cancer risk.
Omega-3 and omega-6 fatty acids compete metabolically for many of the same enzymes, Dr. Hardman explains. When the enzymes are paired with omega-3 fatty acids, they produce beneficial molecules that tend to be anti-inflammatory and promote cancer cell
death. The enzyme activity with omega-6s, however, promotes harmful inflammation, cell multiplication and less cancer cell death.
Omega-3s 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-6s are found in vegetable oils, such as corn, safflower, sunflower and soybean oils. They are often used in commercial snack foods, baked products and salad dressings. Omega-6 oils have a place in a healthy diet, as long as they are eaten in a healthy proportion to omega-3s.
Unfortunately, the ratio of omega-6s to omega-3s in the current American diet ranges from 10:1 to 15:1. Such a high omega-6 to omega-3 ratio is linked to numerous diseases, including cancer, heart disease and inflammatory conditions like arthritis. In healthy populations that consume traditional plant-based diets, the ratio ranges from 2:1 to 4:1 (omega-6: omega-3).How Much Is Enough?
Scientists are not yet certain exactly how much omega-3 fat is needed to reduce cancer risk or enhance cancer treatment. However, AICR recommends eating 3-ounce servings of different types of fatty fish twice a week.
Although fish oil supplements can provide a hefty dose of omega-3s, they raise serious concerns for some people, including diabetics. Individuals who have bleeding disorders or are taking blood-thinning medications (such as aspirin) daily should not use fish oil supplements because they decrease the ability of blood to clot. Those undergoing cancer treatment should get their doctor's approval before taking fish oil or any other dietary supplements. Anyone who does take fish oil supplements should limit daily doses to 1,000 mg to avoid health problems.
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