Nutrition Notes
Week of September 29, 2008
Contact: Sarah Wally, (202) 328-7744

Fish Still Our Best Source of Omega-3 Fat

Karen Collins, MS, RD, CDN
American Institute for Cancer Research

Fish offers our best dietary source of omega-3 fat, the type of fat identified as protective against heart disease, dementia, inflammation and potentially cancer. But with several different types of omega-3s and varying amounts in different varieties of fish and other foods, consumers are often confused about how best to maximize their dietary intake.

Omega-3 fat includes both ALA, which is found in plant foods such as flax, walnuts and canola oil, and EPA and DHA, found only in seafood and algae. Health experts used to consider all three together when evaluating the benefits of omega-3 fats, but evidence increasingly shows that humans are relatively inefficient at converting ALA into EPA and DHA.

Unfortunately, most Americans do not eat enough fish to obtain the levels of EPA and DHA identified as protective. Fish consumption averages about 2.5 to 3 ounces a day in the U.S., much of which includes fish that is relatively low in omega-3 fat like shrimp, pollock, tilapia and catfish. To meet current recommendations, Americans are encouraged to choose fish that are naturally high in fat: examples include salmon, mackerel, trout, sardines and albacore (white) tuna.

The good news: A mere 8 ounces of fatty/oily fish per week is all that is needed to reach the recommended amount of omega-3s for preventive heart health benefits (500 milligrams of EPA and DHA per day). People who already have heart disease should try to average 1000 mg per day, consuming about 16 ounces of fatty fish per week. Those with elevated blood triglycerides may benefit from 2000 to 4000 mg a day, but this will almost always require supplements and should be taken under a physician’s care.

With EPA and DHA-specific recommendations, questions arise about whether vegetarians and others who don’t eat fish can get equal health benefits from high intake of ALA. Several studies link higher ALA consumption with lower heart disease, but it’s not clear whether nonfish-eaters are protected through dietary sources like flaxseed oil and walnuts alone, or if using EPA and DHA-fortified foods or algal supplements provides further protection.

The protective effects of omega-3 fats seem to come by increasing body production of anti-inflammatory hormone-like compounds called eicosanoids. But this benefit may be diminished if other polyunsaturated fats – omega-6 fats – are eaten in excess. These fats (found in corn and safflower oil and fish like farmed tilapia and catfish) boost production of different eicosanoids that increase inflammation. While some research focuses on finding an ideal dietary ratio between the two fats, this approach is hotly debated. Rather, many experts recommend that we simply focus our attention on increasing the amount of omega-3 sources in our diet. The best advice to meet this goal: Eat at least two servings of high omega-3 fish (oily fish) per week.

Today research is giving us a clearer picture of how omega-3 fat protects our hearts; promoting normal blood pressure, heart rhythm and blood clotting seem to be its strongest effects. Studies also show that omega-3 fat, in utero and during infancy, clearly benefit babies’ visual and nervous system development. Experts are trying to encourage women of childbearing age to consume 8 to 12 ounces of seafood weekly, simply avoiding those fish highest in mercury.

Lastly, researchers are starting to look at a potential link between omega-3 consumption and cancer protection. While a major report on diet and cancer risk did not find any concrete evidence, it did note that some emerging (though limited) research suggests a link between fish consumption and lower risk of colon cancer. Additional laboratory studies suggest that omega-3’s anti-inflammatory effects could reduce cancer development, but studies are not consistent. If a link does exist, it is possible that the benefit of omega-3 fish is being obscured by studies that look at total fish consumption, grouping fish high in omega-3 fat together with low fat fish and batter-covered fish high in omega-6 fat.

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