Cruise any grocery store, and you'll find packages of enriched eggs, orange juice, margarine, and even peanut butter emblazoned with enthusiastic statements about their omega-3 content. Marketers have taken health research on the fatty acids and run with it, but there's more to the omega story than is apparent on food packaging.
The case for omega-3s' role in heart protection is stronger than ever. A recent study led by epidemiologist Akira Sekikawa of the University of Pittsburgh, for example, found that eating lots of fish rich in omega-3s may protect against atherosclerosis. Prior research had suggested omega-3s may help control or protect against rheumatoid arthritis, cancer, asthma, depression, and other conditions. Yet omega-3s are not all the same. Those from fish may be more beneficial than those found in plants (and typically used to fortify processed foods). What's more, scientists disagree over the role played by related fatty acids called omega-6s; some believe they can be harmful if out of balance with omega-3s.
Essential fats. Both kinds of fatty acids serve critical roles—omega-3s assist neurological development and help reduce excess inflammation, for example, while omega-6s aid blood clotting and help battle infection. The human body can't make either substance from scratch, so we must get them from food sources. The American Heart Association recommends getting at least two weekly servings of fish, preferably fatty, omega-3-rich varieties like salmon and tuna. But the typical American diet provides scant omega-3 and loads of omega-6. And a recent study suggests that certain kinds of nonfatty, farm-raised fish—tilapia and catfish—may actually worsen that imbalance.
Fatty fish is generally the best source of two types of omega-3s—eicosapentaenoic acid and docosahexaenoic acid —that the human body needs. Plant sources like flaxseed, canola oil, and walnuts contain a different kind of omega-3—alpha-linolenic acid—that has a shorter chain of carbons. In the body, "plant-derived omega-3 fatty acid can be elongated to EPA or DHA, but the conversion rate is extremely low—about 5 percent or less," says Pitt's Sekikawa. By comparison, omega-6s are abundant in vegetable oils used in processed and baked foods (including soybean, corn, and cottonseed oils) and also in meats and egg yolks.
Experts diverge on whether Americans' considerable intake of omega-6 should be of concern. Some theorize that excess consumption of omega-6s may contribute to harmful inflammation and encourage cardiovascular disease, and a 2004 study in people suggested that a type of omega-6 called arachidonic acid promotes inflammation that may lead to atherosclerosis in genetically susceptible people. According to Floyd Chilton, director of Wake Forest University's Center for Botanical Lipids, the ratio of omega-6 to omega-3 in the typical American diet has gone from about 2 to 1 in previous generations to as high as 40 to 1 today. That shift, he says, is "at least partially responsible for the epidemic of inflammatory diseases" such as asthma, arthritis, and diabetes.
The case against an overload of omega-6s isn't airtight, however. A study of some 2,200 people published in the journal Hypertension in July showed a relationship between high intake of omega-6, mostly from vegetable oils, and slightly reduced blood pressure. "Omega-6 fatty acids are not unhealthy," says Robert Eckel, past president of the American Heart Association. "In animals," he says, "they may be precursors to inflammatory molecules, [but in people] the clinical evidence for harm just isn't there." Other experts believe we can avoid a debate over omega-6 altogether. Says cardiologist Stephen Nicholls of the Cleveland Clinic: "Let's praise the virtues of [omega]-3 rather than get bogged down in the issues of [omega]-6."
Supermarket selections. But conscientious consumers are still left to make decisions. Last month, in the Journal of the American Dietetic Association, researchers led by Chilton analyzed the omega-3-to-omega-6 ratios in commonly eaten fish and found that farmed tilapia and farmed catfish skew considerably toward omega-6 and were low in omega-3. By comparison, farmed salmon and trout have far more favorable ratios. "Not all fish are made the same," Nicholls notes.