These good-for-you fats are found in foods from fish to flax and are increasingly popular thanks to the host of benefits they may provide.

Research on the potential health benefits of omega-3 fatty acids has been under way since the 1970s, when Danish scientists discovered that eople who eat more fish have lower risks of heart disease. But the findings were often eclipsed by the low-fat, no-fat movement of the 1980s and early 90s.

“I think omega-3 fatty acids were overlooked for a long time,” says Mary-Ellen Camire, PhD, professor of food science and human nutrition at the University of Maine. “The more we study them, the more benefits we see.”

As notions about dietary fat changed and researchers explored the links of omega-3s to the possible prevention of diseases from asthma to Alzheimer’s, consumers took notice. Americans’ per capita consumption of fish, a top source of omega-3s, has risen to record highs. Food manufacturers also have caught on; the number of omega-3 fortified foods is projected to grow by 60 percent next year, according to product research firm Packaged Facts.

We turned to the experts―scientists, nutritionists, doctors―to learn more about omega-3 fatty acids and if they do indeed live up to their promise.

Basic facts
There are three types of omega-3 fatty acids. Two are found mostly in coldwater fish and are called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). “Fish that live in cold water have adapted to have higher omega-3s so that the fat in their tissues stays liquid, almost like antifreeze,” Camire says. Salmon ranks highest in omega-3s, followed by trout, white tuna, king mackerel, sea bass, herring, oysters, and sardines. The third type of omega-3 is called alpha-linolenic acid (ALA) and is found in plant sources, such as flaxseed, English walnuts, sunflower seeds, canola oil, soy, wheat germ, and dark, leafy greens.

Unlike the fat in a porterhouse or French fries, omega-3 fatty acids are polyunsaturated, so they don’t cause the plaque build-up in arteries that can lead to heart disease. In fact, when substituted for saturated or trans fat, polyunsaturated fats raise “good” high-density lipoprotein (HDL) cholesterol, helping to lower the risk of cardiovascular disease, according to the American Heart Association.

Your body absorbs and uses each type of omega-3 in different measures. Most potential health benefits are attributed to EPA and DHA, which are readily absorbed and put to use. Enzymes in your liver convert plant-sourced ALA to EPA, and to a lesser extent, DHA, but this process is inefficient. “When you eat plant sources of omega-3, only about five percent is converted to EPA,” says Penny Kris-Etherton, PhD, professor of nutrition at Pennsylvania State University. For this reason, many scientific studies use fish and fish oil, which both contain fats composed mostly of EPA and DHA, interchangeably.

Read on for the health benefits of Omega-3s.