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How does oxidation occur?

  • Oxidation occurs when unsaturated fats—such as the omega-3 fatty acids EPA and DHA—are exposed to heat, light, or oxygen.
  • The greater the degree of unsaturation (the more double bonds present), the more susceptible the fatty acid is to oxidation. That is, polyunsaturated fats are more prone to oxidative damage than monounsaturated fats.

How can you tell?

  • Fish oil that has sufficiently oxidized will have a pungent odor, off-flavor, and possibly gel-capsule discoloration.
  • Often, fish oil will contain flavors—typically added to make the taste more palatable—that may mask its natural scent and flavor, hiding signs of possible rancidity.
  • It’s generally considered that gel capsules offer more protection against oxidation than do liquid formulations, as they are air-tight. It also reduces or eliminates the fish odor/taste, making the supplement more palatable.

What happens at the molecular level that makes oxidation so bad?

Generally, oxidation (the removal of an electron) produces a reactive species that tries to restore its electron balance by stealing an electron from other molecular structures that will yield them. The chemical stability of the oxidant determines its capacity to cause cellular damage. In the case of fatty acids:

  • The unsaturated fatty acid itself is converted into an oxidant.
  • The fatty acid’s metabolic intermediates—such as malondialdehyde (MDA) & 4-hydroxy-2-nonenal—also become pro-oxidative species.

Related: What Are Antioxidants and How Do They Work?

Oxidation and Health

  • Generally, oxidation is a chemical process that, if not quelled, may ultimately lead to cell death by compromising cellular membrane integrity or by damaging other proteins, lipids, or DNA.
  • Oxidized fish oil suffers from reduced EPA/DHA potency—the fatty acids primarily responsible for fish oil’s health claims. But can consuming oxidized supplements actually cause harm?

What does the clinical literature reveal?

  • The majority of clinical evidence suggests that consuming fish oil—in both oxidized and non-oxidized forms—failed to lead to lipid peroxidation in healthy human adults.
  • Limited evidence suggests lipid peroxidation may occur following DHA consumption and after the combination of fish oil & exercise (prevented with the preservative antioxidant vitamin E).
  • Animal studies suggest that DNA damage becomes more probable in susceptible populations, such as the elderly.
  • Taken together, available evidence suggests oxidation of fish oil should not be a concern in humans.

Even with current data suggesting that fish oil oxidation should not be a health concern, it is still preferable to maintain biological functionality and reduce the risk of any negative health consequences. Here’s what you can do to prevent oxidation:

  • Buy small amounts at any given time to prevent oxidative-damage accumulation over time. Most brands will recommend that fish oil be used within 3 months of purchase. To reduce the risk of a spoiled product, aim for an even shorter life-span.
  • To prevent exposure to heat and humidity, consider storing the supplement in the refrigerator/freezer, if the packaging instructions recommend to do so. This may also reduce “fishy burps” and create a time-release effect. Be sure to read storage directions—often, capsules may be kept at room temperature unopened and refrigerated thereafter.
  • To prevent exposure to oxygen, store in airtight containers. Glass, PET (polyethylene teraphthalate), or high-density polyethylene (HDPE) containers, especially of the black/opaque variety, may often be the best choices to minimize exposure to light/damage by the sun.
  • Look for added antioxidants on the Supplement Facts label—these typically include vitamin E, rosemary extract, or astaxanthin—that could slow or prevent the oxidative process.

Sources

  1. Header Image: Peter Rosbjerg (Flickr)
  2. Is Your Fish Oil Rancid – Omega-3 Innovations
  3. Lipid Peroxidation – Oxidation in Foods and Beverages and Antioxidant Applications
  4. Fish Oil Consumption & Rancidity – European Food Safety Authority
  5. Flavors and Odors in Fish Oils – Journal of the American Oil Chemists Society
  6. Risk Assessment of Oxidized Fish Oil Products – Norwegian Scientific Committee for Food Safety
  7. Autoxidation of Fish Oil without Oxidants – Journal of Nutrition
  8. EPA Autoxidation – Journal of Biological Chemistry
  9. Chemistry and Biochemistry of Oxidized Fatty Acid – Journal of Free Radical Biological Medicine
  10. Omega-3 Fish Oil Peroxidation – Journal of the American Chemical Society
  11. Malonyl Dialdehyde in Lipid Peroxidation – Journal of Analytical Biochemistry
  12. Metabolic Mechanisms of Fatty Acid Peroxidation – Journal of Free Radical Biological Medicine
  13. Oxidized Fish Oil and Oxidative Stress in Humans – British Journal of Nutrition
  14. Fish Oil and Oxidation In Postmenopausal Women – Journal of Lipid Research
  15. EPA/DHA Supplementation and Oxidative Stress – American Journal of Clinical Nutrition
  16. DHA and Oxidative Stress – Journal of Atherosclerosis
  17. Fish Oil and Oxidative Stress at Rest and After Exercise – Journal of Applied Physiology
  18. DHA and Oxidative Stress in Older Rats – Journal of Free Radical Research
  19. Fish Oil – Examine.com
  20. Health Benefits of Fish Oil After Oxidation – Nutrition Research Reviews
  21. Omega-3 Fatty Acids and Cancer – American Journal of Clinical Nutrition
  22. Fish Oil Packaging – Barlean’s Q&A
  23. Fish Oil: What the Prescriber Needs to Know – Rheumatology Dept., Royal Adelaide Hospital
  24. Gamma-linolenic Acid – University of Maryland Medical Center
     

Research, find, and buy the best supplements.

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