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United States Department of Agriculture

Agricultural Research Service

Fish for Health
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By Forrest Nielsen

Many people are surprised when told that it is not a vitamin or mineral but two fatty substances that may have the most far-reaching health benefits when consumed in higher than usual amounts in U.S. diet. The substances are omega-3 fatty acids known as docosahexanoic acid or DHA, and eicosapentaenoic acid or EPA. These polyunsaturated fatty acids with a long carbon chain backbone are high in certain fish oils and thus often are found in supplements as fish oil. Claims have been made of the benefits of DHA and EPA based on a large amount of carefully done scientific studies, unlike claims for many herbal supplements.

Interest in fish oil began when it was observed that Eskimos living on diets high in foods from the sea, including whale fat, had lower heart disease deaths than Danish people eating diets high in saturated fats such as lard, but low in omega- 3 fatty acids. Since then, numerous studies have found that higher intakes of DHA and EPA reduce the risk of heart attack, stroke and atherosclerosis (hardening of the arteries) and may improve blood pressure.

After scientists found reasons why the long-chain polyunsaturated omega-3 fatty acids were beneficial to heart health, other health problems that could be beneficially affected in a similar manner were studied. This resulted in finding many other health benefits. DHA, especially in the form of breast milk, enhances eye and brain development in babies, which results in better vision and learning ability. The fatty acids inhibit bone loss that results in osteoporosis. Some studies suggest that DHA fights psychological stress and can reduce the development of depression. Other studies have found that DHA and EPA supplementation reduced joint tenderness and stiffness associated with rheumatoid arthritis and improved inflammatory intestinal diseases such as ulcerative colitis. Increased dietary intakes of DHA and EPA have been associated with a reduced risk of prostrate cancer. Animal studies suggest that DHA improves male fertility and the ability to smell and protects the brain from damage caused by Alzheimer's disease.

A good diet - one that provides essential and beneficial nutrients in ample amounts - helps in gaining benefits from consuming DHA and EPA. For example, decreasing intakes of omega-6 fatty acids (high in safflower and corn oils) and saturated fatty acids promotes the beneficial action of DHA and EPA.

Still, these fatty acids will not prevent bone loss caused by an inadequate calcium and vitamin D intake. Animal studies at the Grand Forks Human Nutrition Research Center show that a diet rich in boron is needed for the omega-3 fatty acids to improve bone strength.

Although DHA and EPA have many health benefits, they are not considered essential nutrients. As a result there is no RDA (recommended dietary allowance) for these fatty acids. An intake of 1.0-1.6 grams per day of alpha-linolenic acid (ALA), an omega-3 fatty acid that the body can use to make EPA and DHA is recommended by the Food and Nutrition Board. Foods high in ALA include canola oil and flax seed. Unfortunately, most people do not consume diets containing foods high in ALA. In addition, humans are not good at converting ALA to EPA and DHA. Because fish, especially cold water fish such as salmon, cod, halibut and lake trout, are high in EPA and DHA some health officials have recommended that people should consume two to three servings of fish per week. Because average consumption is about one fish serving per week, most North Americans fail to obtain the maximum benefits provided by EPA and DHA. In the United States, the average estimated daily intake of EPA plus DHA is .13 grams. An additional two servings per week of foods rich in EPA and DHA should increase the intake to over 250 mg per day. In addition to fish, other foods containing fair amounts of DHA and EPA are shrimp, crab, lobster, oysters, scallop and egg yolk.

Last Modified: 10/23/2006
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