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Fish vs. Flax for Omega-3: Which is better?


Dear Dr. Blonz,
I have read that fish oil supplements may be contaminated due to pollution of the seas. Is a supplement that contains flax seed oil a better alternative as a source for the omega-3 fats? PZ, London

Dear PZ,
I recommend the eating of fish over taking fish oil supplements. Population studies have shown that those with a regular consumption of fish have a lower risk of several chronic diseases, including heart disease, hypertension and certain inflammatory conditions, such as arthritis. Your question, however, relates to supplements, so let's first look at the differences between fish oil and flaxseed oil. I will follow this with a few comments on the pollution issue.

Health benefits from the consumption of fish, or from fish oil supplements, are related to the specific omega-3 fatty acids they contain. Fish containing high levels of omega-3s include salmon, mackerel, tuna, herring, yellow tail and trout.

You can, however, also find omega-3 fatty acids in flax seed, and to a lesser extent in canola and walnut oils. But and this is key all omega-3 fatty acids are not the same. In particular, the ones found in flaxseed and other plants are not the same as those found in fish.

What's the difference? To answer this will require a little biochemistry.

It helps to appreciate that oils are made up of fatty acids, and all fatty acids are primarily long chains of carbon atoms that are bonded together.  The omega-3s fatty acids in fish, are often referred to by the initials EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), and they are 20 and 22 carbons long respectively. The omega-3s in flaxseed and other plant sources are called linolenic acid, and it is only 18 carbons long.

Most people need more omega-3 fats in their diet, whether they come from fish or flax, but the key benefits come from EPA and DHA. The body has an ability to take the 18 carbon long omega-3 from flaxseed and lengthen them into EPA and DHA, but it is not an efficient process.

The bottom line is that if you are looking for omega-3 fats, the two supplements are similar, but certainly not equal. It is, however, better to have the omega-3s from flaxseed than to not have any at all.

I would be remiss if I didn't point out that flaxseed has other health attributes. It is an excellent source of lignan, a phytochemical that may have cancer protective effects. Flaxseed also is also an excellent source of dietary fiber.

What about the pollution factor?

The pollution of the seas is a disturbing topic, and it is true that some fish have been affected. Because fish from polluted waters can be sources of contamination, its best, when eating fish, to avoid those caught or raised near industrial plants, sticking instead with offshore or deep-sea areas, or from lakes and streams known to be free from harmful chemicals. In this case, guidance from a reputable fish market should be sought.

Where supplements are concerned, it is best to check individual products to find one that is free of contaminants. There are processes that allow manufacturers to filter out environmental toxins without affecting the level of the omega-3 fatty acids. Look for the appropriate descriptive claims on the label stating that the product is contaminant free. If in doubt, give the manufacturer a call.

One final note: fish oil supplements should be avoided by those with bleeding disorders, or if you are on anticoagulant medications. Caution is also dictated for those with high blood pressure. Always consult your physician if you have an questions.

Dr Blonz Do you have a question that involves nutrition, health and wellness? Dr. Ed Blonz holds an M.S. and Ph.D. in nutrition, and has more than 30 years of experience in the fields of nutrition, foods and health. He is the author of seven books and writes the nationally syndicated column, "On Nutrition," available through Universal Press Syndicate.

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Copyright Ed Blonz, Ph.D.