When you take fish oil, do its omega-3 fats generate damaging free radicals in your body?

The short answer is "no” …despite what some (under-informed) health writers and sellers of fish oil may say.

The myth began because the omega-3 fatty acids found in seafood
EPA and DHAoxidize relatively rapidly when exposed to air (Oxidized omega-3s emit the "fishy” smell that signals a spoiled, unhealthful state).

Key Points
  • Omega-3 fish fats were (again) clinically proven to reduce, not raise, body levels of free radicals and the oxidative stress they can cause in the body.
  • Aussie-French clinical trial confirms the findings of at least four other trials with similar results.
Years ago, some lab studies suggested that consuming concentrated amounts of fish fats from supplements might raise body levels of the unstable oxygen molecules called free radicals.

Free radicals tend to oxidize other molecules in the body, and this propensity initiates a cell-damaging, self-perpetuating chain reaction call "oxidative stress”.

Despite persuasive new clinical and lab evidence to the contrary, some people keep repeating the myth that dietary omega-3s act as "pro-oxidants” in the body unless you take them with supplemental antioxidants.

Free radicals, oxidation, inflammation, and disease
People naturally produce unstable oxygen-based molecules called free radicals as a byproduct of metabolizing foods.

Free radicals play an important role in a range of bodily functions.

But an excess of free radicals
a condition called "oxidative stress”can overwhelm the body's own antioxidant defenses.

Chronic oxidative stress is linked to increased risk of cancer, Alzheimer's, and cardiovascular disease.

High, hard-to-control levels of free radicals yield oxidative stress and can result from normal aging, smoking, stress, pollution, sunlight, hard exercise.

And excessive intake of sugars, white starches promotes free-radical-generating compounds called advanced glycation end products (AGEs)… an oft-overlooked but substantial source of ongoing oxidative stress.

They often recommend taking extra vitamin E... small amounts of which are added to standard, refined fish oils to help stop oxidation in the capsule.

Alternately, they may suggest taking supplements of the more powerful antioxidant called astaxanthin (ass-tuh-zan-thin).

Astaxanthin also occurs naturally in wild salmon and krill, and in unrefined krill oil and our wild salmon oil, where it preserves the oil's integrity by blocking oxidation of omega-3s very effectively.

Evidence for omega-3s antioxidant effects dates back several years
Seven years ago, the results of a controlled clinical trial seriously undermined the idea that the omega-3s we ingest from fish or fish oil pills might generate free radicals… and thereby increase oxidative stress in our bodies (Mori TA et al. 2003).

And as we reported in 2008, not only did the results of a cell study and four clinical studies rebut omega-3s that assertion, they showed that omega-3s lower free radical levels in the body overall, and in specific cells and tissues.

For more on those findings, see "Surprise! Omega-3s May Exert Antioxidant Impacts”.

In addition to those studies, a clinical trial in healthy people also found that omega-3s produced a cut in oxidative stress. (Nalsen C et al. 2006).

Now, the outcomes of a new Australian clinical trial confirm that omega-3 fish oils actually reduce levels of free radicals and oxidative stress in the body.

And, of great importance, the new findings affirm prior indications that omega-3s reduce oxidative stress by means other than via their proven inflammation-moderating effects. (The cluster of immune responses that doctors call "inflammation” invariably includes the intentional creation of free radicals.)

Aussie-French trial reaffirms the antioxidant effects of fish oil
Once again, the results of a controlled clinical trial indicate that the two major omega-3 fats in fish
EPA and DHAreduce oxidative stress in the body (Mas E et al. 2010).

Scientists from Australia and France now report that, over a six week period, a standard measure of oxidative stress dropped by about 20 percent in people who took daily fish oil capsules providing either EPA or DHA.

The Aussie-French team recruited two groups of volunteers of 59 each:
  1. Overweight men with moderately unhealthy blood fat/cholesterol profiles (men aged 20 to 65)
  2. Diabetics with high blood pressure (men and post-menopausal women aged 40 to 75)
The participants were randomly assigned to follow one of three daily supplement routines for six weeks:
  • Four grams of EPA (in fish oil)
  • Four grams of DHA (in fish oil)
  • Refined olive oil (placebo)
People's blood levels of compounds called F2-isoprostaneswhich are created when bodily fats get oxidized by free radicalsprovide an accurate picture of the levels of oxidized fats and overall oxidative stress in the body.

Adding to the positive picture, blood levels of an essential but generally pro-inflammatory omega-6 fat call AA (arachidonic acid) dropped in both omega-3 groups.

Their final statement came to a clear conclusion: "The data, therefore, suggest 3 fatty acids reduce oxidative stress, which is likely related, at least in part, to their anti-inflammatory actions…” (Mas E et al. 2010).

And they made an obvious inference, given the proven role of chronic inflammation as a major factor in the formation
and potentially fatal ruptureof arterial plaque:

"These findings give further support for supplementation of the diet with 3 fatty acids for cardiovascular risk reduction” (Mas E et al. 2010).

Note: The fish oils were supplied by the U.S. National Institutes of Health, and the study was funded by Australian non-profit and public bodies.

Did the cut in oxidative stress stem from omega-3s' anti-inflammatory role?
Importantly, although the EPA and DHA groups showed reductions in blood levels of omega-6 AA, the scientists found no statistical link between a drop in the omega-3 groups' average omega-6 blood levels and their substantial reductions in levels of markers for oxidative stress.

As they wrote, "Therefore, the changes in F2-isoprostanes most likely reflect a true [direct] reduction in oxidative stress, rather than resulting from a reduction in the supply of substrate [i.e., omega-6 fat].”

By this they meant that both omega-3 groups showed reductions in their blood levels of inflammation-related immune system cells called leukocytes, which normally generate free radicals.

In addition, the levels of pro-inflammatory omega-6 fats dropped in the groups taking omega-3s.

This happens gradually when you increase your omega-3 intake… and displacement of pro-inflammatory omega-6s in your cells by anti-inflammatory omega-3s happens even faster and more fully when you also lower your omega-6 intake.

The omega-6 overload in American diets
Dietary omega-6 and omega-3 fats serve as the raw material (substrate) from which our cells make key immune system agents (autocoids), which help control free-radical-generating inflammation and the oxidative stress it produces.

Omega-6 fats often serve as the source of pro-inflammatory agents and omega-3s almost always yield anti-inflammatory agents.

Sadly, the American diet is wildly imbalanced in favor of omega-6 fats
with proven bad consequences for disease risk and overall health.

This because omega-6 fats abound in the cheap vegetable oils common in kitchens and in most packaged, prepared, and restaurant foods.

Omega-6 fats predominate in most common oils other than olive, macadamia, canola, and "hi-oleic" sunflower oils.

Canola oil and soy oils alike provide higher proportions of plant-form omega-3s (6-9 percent) than other common oils (0-3 percent).

However, the higher omega-3 levels of canola oil and soy oils is a minor advantage at best, because human bodies only convert two to 10 percent of the plant-form omega-3s we eat into the long-chain, "marine" omega-3s (EPA and DHA) our bodies actually need for critical body functions.

And both canola and soy oil are higher in omega-6 fats than the alternatives we've listed above... with soy being much worse in this regard (Soy oil contains about 53 percent omega-6 fat, versus about 20 percent omega-6 fat in canola).

The remaining fats in canola and soy  are "neutral" monounsaturated fats, which predominate much more in all of the alternative oils we recommend and are more heat-resistant than omega-3 or omega-6 oils.

If you have no other food or supplemental source of omega-3s, eating lots of soy or canola oil will meet your bare minimum omega-3 requirement... but otherwise, they are not ideal oils.

Omega-3s and air don't mix
Today's report confirms that dietary omega-3s actually reduce free radical and oxidation levels.

But their vulnerability to rapid oxidation once exposed to air
and slower oxidation inside a harvested fishexplains why fish can start smelling funky pretty fast... unless, like ours, it's kept cold until being flash-frozen within hours of harvest.

This also explains why quality conscious fish mongers
including Vital Choiceprefer flash-frozen fish.

While supermarket fish cases often feature frozen fish that's been fully or partially thawed, we will sell only fish that's been kept frozen continuously, through its delivery to your door.

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  • Mas E, Woodman RJ, Burke V, Puddey IB, Beilin LJ, Durand T, Mori TA. The omega-3 fatty acids EPA and DHA decrease plasma F(2)-isoprostanes: Results from two placebo-controlled interventions. Free Radic Res. 2010 Jun 14.
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