Fish oil supplements are popular across the UK and the US because they are rich in omega-3 fatty acids, but independent tests have found that more than 1 in 10 common fish oils are “rancid”.
Analysis of 64 fish oil supplements, which are sold under 60 large US retail brands and available globally, revealed that some recorded rancidity levels 11 times higher than recommended limits.
Labdoor, which analyses supplements and vitamins for purity, label accuracy and nutritional value, tested the fish oils for total omega-3s, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), vitamin D and CLA (conjugated linoleic acid) content.
It also analysed total oxidation values, which measures the freshness of each oil against international voluntary standards of rancidity.
Fish oil turns rancid when it becomes oxidised and can be characterised by a strong fishy taste and a sour, off odour. A number of products add flavours, such as citrus, to mask the rancidity as well as the fishy taste and smell of the oils.
About 10 per cent of the brands analysed had levels of oxidised fish oil high enough to be considered rancid, Labdoor’s report said.
Voluntary limits of oxidative quality created by the Global Organisation for EPA and DHA Omega-3 (GOED) are set at 26. The higher the number, the more rancid the oil is.
Fish oil has been labelled by previous studies as “extremely susceptible to oxidative degradation” due to its long supply chain.
One study, published in the Journal of Nutritional Science, detailed the journey from ocean catch to final consumer product, noting that the major sources of fish oil are from fish caught off the coast of Peru and Chile.
Catches are transported on a fishing vessel to shore, where it is then processed into crude fish oil, alongside other fish products. The oil is stored in large tanks before being shipped around the world for further refining.
“Less than 25 per cent of the total crude fish oil supply is destined for human consumption and undergoes additional refinement and deodorisation,” wrote the authors of the study.
“The end result is that consumers are at risk of purchasing an oxidised supplement, for which there is little tangible information on the packaging to provide details of the oil’s original source, age and levels of refinement.”
Labdoor’s analysis, which was conducted between 2014 and 2018, found some fish oils sold under the brand names Carlson Labs and Puritan’s Pride had significantly higher rancidity grades than the suggested limits.
Some products from Ocean Blue and Nature’s Answer were also found to have exceeded the limits, and half of all the products tested bordered on the GOED limit.
However, higher rancidity levels do not indicate that the oils are less safe, but rather lower in quality. It remains unclear if rancid fish oil is harmful to human health, but studies have shown they are less effective than fresh fish oil.
The Independent has contacted Carlson Labs, Puritan’s Pride, Ocean Blue and Nature’s Answer for comment.