& Joannie Dobbs Monday,
Fatty acids are not all created equal
The omega-3 fatty acids in fish oils are known to provide a variety of health benefits. But many people are concerned about eating fish for a number of reasons. Some types of fish can be high in mercury. Increasing demand for fish is straining the world's supply of fish, and various types are becoming depleted. Even fish farming has detractors among those concerned about potential environmental impact.
Question: Are there good food sources of omega-3 fatty acids besides fish?
Answer: Many plant oils supply an omega-3 fatty acid called alpha-linolenic acid (ALA). Flax (linseed) oil is extremely high in this fatty acid. Other good sources include walnuts, canola oil and soybean oil.
But the ALA found in these plant oils is not the same as the type of omega-3 fatty acid found in fish oils, nor does it provide the same benefits.
In fact, a high intake of ALA is associated with an increased risk of health problems such as prostate cancer and macular degeneration in the retina. In contrast, the fish omega-3 fatty acids, EPA and DHA, help to prevent these conditions.
Q: Are there any plant sources that provide the fish fatty acids EPA and DHA?
A: Other than dietary supplements containing a high-DHA algae oil, no good plant sources of EPA and DHA are currently available. But new developments are on the horizon.
Scientists in Germany recently developed a genetically modified flaxseed that produces oil containing small amounts of EPA. Future work on this oilseed might result in a good plant source of EPA.
Another promising development involves the genetic modification of seeds that produce canola oil. Researchers at the Monsanto Co. in Davis, Calif., developed a seed that produces very high levels of a fatty acid called stearidonic acid (SDA) which, unlike ALA, is efficiently converted into EPA in the human body.
Q: Is it possible to consume too much omega-3 fatty acids?
A: Yes. Although it is not entirely clear how much is too much, taking excessive amounts of fish oil on a regular basis could impair immune functions and increase the risk of hemorrhagic stroke due to a "blood thinning" effect. Due to this, people taking anticoagulant drugs should use fish oil supplements only with proper medical supervision.
Because scientific information on the risks of a high intake of omega-3 fatty acids is limited, the Institute of Medicine did not establish an upper-limit recommendation. It did, however, provide acceptable ranges of intake, recommending a limit of about 1 to 4 grams per day and that EPA and DHA combined average about 0.1 to 0.4 grams per day. Just a once-a-week serving of salmon or a can of sardines can meet this need.
Q: Are fish oil supplements a safe source of omega-3 fatty acids?
A: ConsumerLab.com recently conducted independent testing of 41 fish oil supplements. Only three had problems. Two had about half of what they claimed on the label, and one was not fresh. None of the products exceeded safety standards for mercury or PCB content.
Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S.
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service
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