Fish Oil and Oxidation: Causes and Effects

Fish Oil

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.