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Catch of the Day

Catch of the Day

October 1998 -- Nutrition Notes

By: Andrea Platzman, R.D.
Contributing Editor

  After decades of blaming fat for a myriad of ills, science is finding strong evidence that by increasing their fat intake, people might strengthen their defenses against heart disease, stroke, rheumatoid arthritis, psoriasis, Crohn's disease, some cancers, and possibly hypertension. There's a catch, though - the fat has to come from fish or other rich sources of omega-3 fatty acids.

  "Omega-3 fatty acids have been shown to cut the risk of heart attacks," says Linda Candler, communications director, National Fisheries Institute, Arlington, VA. "There have been positive effects on arrhythmias and now some promising studies connect omega-3 fatty acids to attention deficit disorder and other neurological disorders."

  An omega-3 (n-3) fatty acid is a polyunsaturated fatty acid (PUFA) in which the first double bond occurs three carbons from the methyl (CH3) end of the molecule. Linolenic acid is the primary member of the omega-3 family. This 18-carbon acid is considered an essential fatty acid because the body cannot manufacture it. The body can make the longer-chain 20- and 22-carbon members of the omega-3 series, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) respectively, from alpha-linolenic acid, albeit the process is less efficient than consuming them directly. Scientists have found evidence to suggest these fatty acids play different, but equally vital, roles in the body.

  Ratios of omega-3 and omega-6 fatty acids, including linoleic (C18:2 n-6) and arachidonic acid (C20:4 n-6), also might contribute to health. Long-chain PUFAs, such as DHA, EPA and arachidonic acid, act as precursors to eicosanoids, hormone-like substances that affect many of the body's processes.

Take heart

  "Consuming omega-3 fatty acids has been shown to significantly lower blood triglycerides in individuals with elevated levels, which has been recognized as a risk factor for cardiovascular disease," says Barbara Schneeman, Ph.D., dean, College of Agriculture and Environmental Sciences, University of California-Davis. Omega-3 fatty acids make platelets less likely to coagulate, which decreases the risk of dangerous blood clots in narrowed arteries. These fatty acids also improve the heartbeat, blood flow and chemical reactions in the blood vessels - all enhancing the blood circulation in the heart.

  While omega-3 fatty acids can reduce heart disease, they have little effect on total blood cholesterol levels. Studies suggest, however, they help promote an increase in the ratio of HDL "good" cholesterol to LDL "bad" cholesterol; lower blood level of triglycerides (fats that might clog the arteries with cholesterol); and reduce blood pressure modestly in people with hypertension.

Other benefits

  In the growing infant, the omega-3 fatty acid DHA helps build brain tissue, affects nerve growth and is required for development of the retina. The fetus receives DHA from its mother's blood and infants obtain it from breast milk. Infants consuming only formula, which, in the United States, typically does not contain DHA, might not consume sufficient omega-3 fatty acids. This can lead to less DHA in their nervous tissue and potentially affect eye development.

  Arthritis sufferers who regularly consume omega-3 fatty acids have seen improvement in tender joints and reduced morning stiffness. Consuming omega-3 fatty acids might ease arthritis pain a bit. However, it should not be considered a replacement for traditional arthritis treatment.

  Preliminary research has shown that omega-3 fatty acids decrease the inflammation of Crohn's disease, a chronic problem characterized by intermittent episodes of intestinal inflammation. However, many patients suffering from this disease don't consume a lot of fish oil because it sometimes leads to gas, bad breath or a fishy body odor. Using omega-3 fatty acids in supplement form to decrease these symptoms is currently being researched.

  Other potential health benefits are being investigated. Some psoriasis patients have found that using fish oil helps to reduce the disease's itching and redness. Omega-3 fatty acids also might slow or prevent tumor growth. Since the brain requires omega-3 fatty acids for an optimal consistency of brain-cell membranes, new research is currently under way to test a possible link with these fatty acids and depression. But it is too early to suggest that people should eat more fish to relieve depression. At Purdue University, West Lafayette, IN, researchers found that boys diagnosed with ADHD (attention deficit hyperactive disorder) had significantly lower levels of omega-3 and omega-6 fatty acids in their blood, as compared to those without ADHD. Consuming large doses of omega-3 fatty acids might help maintain healthy blood-sugar levels in diabetics, especially in people whose diabetes is not insulin-dependent.

Finding omegas

  Because increasing total fat consumption isn't recommended, replacing some dietary fat with fats containing omega fatty acids is the best way to reap health benefits. The best source of omega-3 fatty acids is from fish, due to their diet of omega-3-rich algae. "Most fish contain some amount of the omega-3 fatty acids, but the fattier, cold-water fish, such as tuna, mackerel and salmon, contain the highest amounts," Candler says. The shorter-chain alpha-linolenic acid can be converted to eicosapentaenoic acid and DHA in the body. This fatty acid is found in plant foods such as spinach, mustard greens, walnuts, flaxseed, soybean and canola oil.

  "To date, the Recommended Daily Allowance for omega-3 fatty acids has not been quantified," Candler says. "However, the Journal of the American Medical Association reported beneficial results consuming fish twice a week, so that's what we recommend."

  Various world health organizations - such as British Nutrition Foundation, Health and Welfare Canada, and the Ministry of Health-Sweden/Finland - suggest daily intakes of 0.5 to 2.0 grams per day of omega-3 fatty acids.

  "Overall, even consuming just one fish meal per week can have a health benefit," says Schneeman. "It is recommended to incorporate fish into a healthy lifestyle."

  Last year, FDA approved fish oil as a GRAS additive, making it a prime candidate for functional foods. "Most nutritionists encourage people to consume fish," Schneeman says. "However, not everyone has the ability to do so. It would be encouraging to have palatable and appealing products which contain omega-3 fatty acids when it is not possible to consume fish."


  Andrea D. Platzman is a registered dietitian who is a consultant to the food industry, and regularly writes for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.


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