The Nation's Health + health

Omega-3 MUST be from fish oil

Despite my rants in this blog and elsewhere, at least once a day I'll have a patient say, "I cut back (or eliminated) my fish oil because I get my omega-3s from _______ (insert your choice of flaxseed oil, walnuts, yogurt, mayonnaise, bread, etc.)."

(See prior Heart Scan Blog post: Everything has omega-3.)

When I point out to them that the "omega-3s" in these products are not the same as the EPA and DHA from fish oil, they invariably declare, "But it says so here on the label: 'Contains 200 mg of omega-3 fatty acids'!"

Apparently, some of my colleagues have even endorsed this concept of replacing the omega-3s from fish oil with these "alternatives."

It's simply not true. The linolenic acid that is being labeled as omega-3, while it may indeed provide health benefits of its own, cannot replace the EPA and DHA that fish oil provides.

The most graphic example of the differences between the two classes of oils is in people with a condition called familial hypertriglyceridemia. People with this condition have triglyceride levels of 400, 600, even thousands of mg/dl--very high. Fish oil, usually providing EPA and DHA doses of 1800 mg per day and higher, reduce triglycerides dramatically. A person with a starting triglyceride level of, say, 900 mg/dl, may take 2400 mg of EPA and DHA from fish oil and triglycerides plummet to 150 mg/dl. This person then decides to replace fish oil with a linolenic acid source like flaxseed oil. Triglycerides? 900 mg/dl--no effect whatsoever.

Familial hypertriglyceridemia represents an exagerrated example of the differences between the two oils. Even if you don't have this genetic condition, the differences between the oils still apply.

EPA and DHA are activators of the enzyme, lipoprotein lipase, that accelerates clearance of triglycerides from the blood. Linolenic acid from flaxseed oil, walnuts, and other food sources does not. EPA and DHA block after-eating (post-prandial) accumulation of food by-products that can contribute to coronary and carotid plaque. Linolenic acid does not. EPA and DHA block platelets, reduce fibrinogen, and exert other healthy blood clot-inhibiting effects. Linolenic does not.

The 11,000-participant GISSI-Prevenzione Trial that showed 28% reduction in heart attack, 45% reduction in cardiovascular death with omega-3s used . . . fish oil .

The 18,000 participant JELIS trial that showed 19% reduction in cardiovascular events when omega-3s were added to statin therapy used . . . fish oil . (Actually, in JELIS, they used only EPA wtihout DHA.)

Linolenic acid is not a waste, however. It may exert anti-inflammatory benefits of its own, for instance. But it exerts none of the triglyceride-modifying effects of EPA or DHA.

EPA and DHA from fish oil and linolenic acid from foods each provide benefits in their own way. Ideally, you include both forms of oils--fish oil and linolenic acid sources--in your daily diet and obtain full benefit from each separate class. But they are not interchangeable.

Copyright 2008 House, MD

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