Many fish oil supplements are rancid, reports find

People’s fish oil subsidies can be even more fishermen than they would like them to be, according to one new report from independent testing company Labdoor. The company claims to have found that a significant number of dietary supplements sold in the market are heavy in oxidized oils, which can make them taste rancid and smell rotten, as well as possibly affect their quality.

Labdoor’s results were reported Monday by the Guardian. The lab tested 54 best-selling fish oil brands marketed in the United States and available elsewhere in the world. About 10% of brands had levels of oxidized oil high enough to be considered rancid, according to voluntary regulatory standards, the report found. Of these offenders, some levels were 11 times higher than recommended.

“It was quite frequent,” Dan Mark, Labdoor’s research director, told the Guardian. “For us, they would start to smell and feel bad.”

Fish oil is rich in omega-3 fatty acids, which are also a type of dietary fat known as polyunsaturated fat. Fats are essential for a healthy diet, but poly- and monounsaturated fats are thought to be the best fats for regularly consume over other types like trans fat and saturated fat. It is less certain whether fish oil and omega-3 fatty acids specifically provide some additional health benefits. Some data has suggested that regularly eating seafood rich in these oils is associated with a modestly lower risk of cardiovascular problems, for example, while other data have not found a similar benefit by simply taking fish oil supplements. Regardless of the mixed data, lots of people are taking fish oil supplements, and that’s it estimated to be a billion dollar industry.

The report is far from the first proof to suggest that a significant proportion of fish oil products are rancid, although estimates are lower from industry-driven studies. Often, these products are flavored to mask any potential odor or taste, which can also obscure the level of oxidation in a product. But aside from aesthetics, too much oxidation can be bad in other ways. Limited data have suggested that oxidized fish oil simply does not provide the same potential benefits as fresh fish oil and may even have a negative effect on blood cholesterol levels.

Oxidation is not the only possible problem with these products. The Labdoor report and other studies have found that fish oil, like other types of supplements, can be dosed inconsistently, as some pills have very different amounts of omega-3 than the labeled ones. Even if you assume that fish oil is worth taking, this inconsistency can mean that users do not get enough of the product to actually benefit from it. As a whole, the supplement industry barely regulated in relation to drugs and other drugs. What’s more, like the Guardian too reported this week, the fish oil industry is contributing to ongoing environmental issues such as overfishing.