Many Fish Oil Supplements Are Rancid, Report Finds

People’s fish oil supplements may be even fishier than they’d want them to be, according to a new report from independent testing company Labdoor. The company claims to have found that a substantial number of supplements sold on 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 findings were reported Monday by the Guardian. The lab tested 54 best-selling fish oil brands marketed in the U.S. and available elsewhere in the world. Around 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 had levels 11 times higher than recommended.

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

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

The report is far from the first piece of evidence to suggest that a sizable chunk of fish oil products are rancid, though estimates are lower from industry-run studies. Often, these products have flavoring added to them to mask any potential odor or taste, which could also disguise the level of oxidization present in a product. But aesthetics aside, too much oxidation could be bad in other ways. Limited data has suggested that oxidized fish oil may simply not provide the same potential benefits as fresh fish oil and could even have a negative effect on blood cholesterol levels.

Oxidation isn’t the only possible issue with these products. The Labdoor report and other studies have found that, much like other types of supplements, fish oil can be inconsistently dosed, with some pills having very different amounts of omega-3s than labeled. Even if you assume that fish oil is worth taking, this inconsistency could mean that users aren’t getting enough of the product to actually benefit. As a whole, the supplement industry is barely regulated relative to drugs and other pharmaceuticals. What’s more, as the Guardian also reported this week, the fish oil industry contributes to ongoing environmental issues like overfishing.