In fish oil, a rancid example can involve a strong fishy taste and rotten smell.
The rancidity is often masked by flavourings, which are added to most fish oils to reduce the fishy taste and smell.“That means if you go out and buy fish oil, there is at least a one in five chance of you getting an oil more oxidised than the recommended level,” said Dr Ben Albert, fellow at the University of Auckland, whose research focuses on the health effects of fish oil.“Flavouring is added to fish oils to help mask fishy smell and taste, and … might make more oxidised oils more palatable for people to take, so it could also be used to hide oxidation of the oil,” said Albert.“Some fish oils will smell more than others, but if they don’t smell bad, that doesn’t tell you it’s not oxidised,” he said.
The GOED maintains that the majority of its members’ fish oil products are within the limits.But according to Labdoor’s analysis, conducted on products between 2014 and 2018, fish oils under the brand names Carlson Labs and Puritan’s Pride, which retail in chains such as Walmart and Amazon, had rancidity grades significantly higher than the suggested limits: 281.8 for Carlson’s Norwegian cod liver oil and 37.1 for Puritan Pride’s soft-gel fish oil.Whether it is harmful or not, rancid oil is likely to be less effective than fresh fish oil, according to Martinsen.