All About Omega-3s
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.
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.[pagebreak]
The strongest evidence links omega-3s to helping the following:
Your heart: It can benefit from omega-3s in a number of ways. They help reduce triglyceride levels, counteract inflammation, keep arteries elastic so blood flows smoothly, and prevent the buildup of plaque deposits that can break off and block an artery―all risk factors for deadly heart conditions.
The most potent effect, however, was discovered in 2006, when Harvard researchers pooled and reviewed heart-health/omega-3 studies and determined that 250 milligrams a day of EPA and DHA from either fish or fish-oil supplements helped reduce the risk of dying from a heart attack by 36 percent. “Omega-3s stabilize each individual heart-muscle cell so that during a heart attack, it’s less likely to beat out of rhythm, called an ‘arrhythmia,’” Dariush Mozaffarian, MD, DrPH, study author and assistant professor of medicine and epidemiology at Harvard University. An arrhythmia can be fatal because it impairs the heart’s ability to pump blood throughout the body.
Your joints: To counter rheumatoid arthritis, omega-3s act at the synovium, a one-cell-thick layer of tissue that encapsulates joints and feeds nutrients to cartilage. Omega-3s decrease the production of inflammatory proteins called cytokines. “Cytokines play a role in stripping cartilage and [eroding] bone,” says Patience White, MD, MA, professor of medicine and pediatrics at George Washington School of Medicine and Health Sciences and chief public health officer for the Arthritis Foundation.
While omega-3s haven’t been proven to stop the progression of rheumatoid arthritis, researchers have found that those who consume EPA and DHA have fewer tender joints and decreased stiffness. For example, last year when University of Pittsburgh scientists gave patients with neck and back pain 1.2 grams of fish oil daily for a month, 60 percent of subjects reported improvement of their arthritic symptoms, so much so that half of them stopped taking nonsteroidal anti-inflammatory drugs (NSAIDs).
Studies in which scientists have compared fish intake across 10 countries have concluded that rates of clinical depression, bipolar disorder, and postpartum depression are nearly 30 to 50 times greater in countries with low fish consumption.
Omega-3s may offer mood-enhancing effects even in those who aren’t diagnosed with mental illness. In a 2007 study, University of Pittsburgh scientists measured fatty-acid levels in 106 healthy adults and asked them to complete mood questionnaires. The researchers observed that people with higher levels of EPA and DHA were less likely to report feeling blue, even when measured against a normative range of depressive symptoms. “That suggests that higher blood levels of EPA and DHA are protective against depression,” says Sarah Conklin, PhD, lead study author and professor of psychology at Allegheny College in Meadville, Pennsylvania. Because brain-cell walls are made up of DHA and EPA, consuming more of these fats may improve brain cell composition and neurotransmitter function, which is dysfunctional in people who are clinically depressed.
Studies have made promising associations, calculating that people who eat fish two to three times a week are about half as likely to experience age-related cognitive decline, including Alzheimer’s disease.
While the causes of Alzheimer’s are not entirely understood, experts believe that inflammation in the memory centers of the brain may play a role. “Senile plaques in the brain [produce] inflammatory proteins,” says Caleb Finch, PhD, professor of gerontology and neurobiology and codirector of the Alzheimer’s Center at the University of Southern California. Some accumulation of these plaques occurs naturally with age, but there is excessive buildup in those with Alzheimer’s. As a result, brain cells die. Reducing the inflammatory status may help prevent progression of the disease.
Although research isn’t conclusive, evidence indicates omega-3s may help decrease severity of asthma and medication use in certain populations, says Jane Burns, ScD, a Harvard researcher. In a 2007 Harvard study of more than 2,000 teens ages 16 to 19, Burns and colleagues determined that those with the lowest omega-3 intake―22 milligrams of total EPA and DHA daily―had a 70 percent increased risk of asthma. Asthma is caused by inflammation in the airways, and omega-3s may help quell that inflammation.
While there’s no official Recommended Dietary Allowance, the Institute of Medicine (IOM)―a government-funded group that supplies the data on which dietary guidelines are built―states that adequate daily intake for omega-3 fatty acids is 1.1 grams for women and 1.6 grams for men. The IOM does not distinguish between ALA, EPA, or DHA.
“The most efficient way to obtain omega-3 fatty acids is from fish,” says Donald Hensrud, MD, MPH, associate professor of preventive medicine and nutrition at the Mayo Clinic College of Medicine in Rochester, Minnesota.
Doing so will ensure that the omega-3s you consume are the two types associated with potential health benefits. The American Heart Association and American Dietetic Association recommend at least two servings (approximately four ounces each) of fatty fish per week.
Supplements and fortified foods
When shopping for omega-3 fortified foods, consider the type of omega-3 that is added. “Most of the food products that say they have omega-3s contain ALA,” Mozaffarian says. Although ALA offers some of the heart-health benefits of any other type of polyunsaturated fat, it has not yet been shown to offer the specific health benefits linked to EPA and DHA. A food is fortified with ALA if the ingredient list mentions flaxseed or canola oil. Foods with added EPA and DHA usually say so on their packaging or list algal oil as an ingredient (algae, unlike terrestrial plants, is a rich source of EPA and DHA, and contains little ALA). For instance, some milk now contains 32 milligrams of DHA per eight-ounce serving. “But there isn’t any good, firm data that these fortified foods will have the same benefits as natural food sources, specifically fish,” Hensrud says.
Plus, as one researcher points out, the omega-3s from fish are just like the vitamins, minerals, and antioxidants in other whole foods in that they may have a synergistic effect. “We aren’t sure if it’s the omega-3 fatty acids alone that are responsible for the benefits of fish,” says Malden C. Nesheim, PhD, provost and professor emeritus at Cornell University and chair of the National Academies’ Committee on Nutrient Relationships in Seafood. It’s possible that other, as-yet-unidentified nutrients in fish may work together with the omega-3 fatty acids to help improve health.
Health and nutrition writer Lauren Russell Griffin lives in New York City.