Help Center

Are rancid oils a health issue?

Rancid oils, whether nutrient rich or not, can have a pro-oxidant (too much oxygen) effect within the body.  This can result in cellular damage.  Such oils should strictly be avoided by infants, children, pregnant mothers and those with impaired immune systems.

The Norwegian Institute of Food, Fisheries, and Aquaculture Research conducted an initial series of in vitro studies on the extra-virgin oils produced at ECO-Marie to determine their effects (versus the popular oils on the market) on oxidative stress parameters.  Preliminary results suggest that the popular oils result in oxidative stress in the human cells tested, leading to cellular damage.  The only oils which did not were the extra-virgin oils.

Research indicates that rancid oils may also inhibit the cells' own antioxidant system and reduces the inflammation-inhibiting effect of omega-3 fatty acids in cell models.  Even more worrying is the fact that rancid fats have been implicated in increased rates of heart disease, atherosclerosis and are possible carcinogenic.

Analytical testing

Various methods can be used for screening and monitoring lipid peroxidation (oxidatie rancidity) including measuring levels of:

  • Peroxide
  • Anisidine
  • Thiobarbituric Acid Reactive Substances' (TBARS)
  • Free fatty acids
  • Acid values


At the initial stages of oxidative rancidity primary oxidation products are produced and the oil will have elevated levels of peroxide and anisidine.  However, once the oil has been in a state of rancidity for a prolonged period of time the peroxide and anisidine values drop to normal or very low levels because the primary oxidation products (i.e. hydroperoxides) have been converted to secondary oxidation products.  If you test an oil that is in an "advanced stage of rancidity" (or putrid) you will see low levels of peroxide and anisidine and assume that the oil is still fresh.  No so!  The low levels are simply because the primary oxidation products have now been converted to secondary oxidation products.  These secondary oxidation products can be detected by measuring TBARS.  Oils which are in an advanced stage of rancidity will also typically have raised TBARS, a dark color and strong taste and smell.  The old time Nrose fishermen and Vikings actually favored the clear/pale golden colored oil that was fresh and health.

As a final note, another form of rancidity is "hydrolytic rancidity" which is evident in oils which have raised free-fatty acid levels and elevated acid levels.


This article applies to: Rosita Extra-Virgin Cod Liver Oil (EVCLO).

Was this article helpful?
0 out of 0 found this helpful
Have more questions? Submit a request