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The benefits of fish oil, according to experts

Americans love their fish oil supplements. In 2012, 18.8 million American adults took them, making them the most popular natural products in the US at the time, per the National Institutes of Health. Although sales of the hazy yellow capsules began to plateau, then dip, in 2013, according to CNN, plenty of people still swear by the supplements for heart, brain, and eye health — but does fish oil actually work?

Fish oil is basically oil processed from fish, primarily species like sardines, herring, and anchovies, which are full of nutrients called omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular — which the body can’t produce on its own. Omega-3 fatty acids have been proven to reduce inflammation, and chronic inflammation has been associated with heart disease, diabetes, cancer, and other age-related conditions. But the science behind many of the health claims about taking omega-3 fatty acids in the form of fish oil supplements remains murky.

Plus, the fish oil supplement industry may be harmful to the planet. The fish caught for supplements are so-called keystone species, which larger fish heavily rely on for food, Paul Greenberg, author of The Omega Principle, told NPR. In fact, some 20 to 25 million metric tons of fish, or a quarter of all fish caught, gets processed into animal feed or supplements. Removing these keystone species can lead to declines in larger fish, which can vastly disrupt marine ecosystems.

With these disclaimers in mind, how do you know whether to start taking fish oil supplements? For which health claims do we have the strongest evidence? Mic asked two nutrition experts to weigh in.

Can fish oil improve my heart health?

Much of the rationale behind claims that fish oil can benefit heart health stem from evidence that omega-3 fatty acids lower levels of triglycerides — a type of fat — in the blood, explains Linda Van Horn, a nutrition professor at Northwestern University’s Feinberg School of Medicine. Elevated blood triglyceride levels are usually accompanied by low levels of high-density lipoprotein (HDL), or “good” cholesterol, and high levels of low-density lipoprotein (LDL), or “bad cholesterol.”

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Although prescription omega-3 fatty acid medications have been shown to lower triglyceride levels by 20 to 30% among most people who need treatment for high triglyceride levels, the American Heart Association advises people against treating themselves with non-prescription fish oil supplements. Since supplements aren’t regulated by the Food and Drug Administration, companies that manufacture them don’t need to prove their safety or efficacy in clinical trials.

Evidence of whether fish oil can lower heart disease risk in healthy people is more dubious. A 2017 scientific advisory from the AHA found there aren’t enough studies to support the use of omega-3 among healthy people to prevent heart disease. “If you’re trying to reduce your risk for cardiovascular disease, it might not be your best approach,” Van Horn says, adding that you’re better off eating a diet high in fish and plant-based proteins, and low in red and processed meat.

Is fish oil good for brain function?

Much of the brain consists of omega-3 fatty acids, which seem to be important for cell signaling. Again, though, whether omega-3-fatty acid-containing fish oil does anything for brain health is unclear. “There is no question” that maternal intake of DHA is important for cognitive development in utero, and in fact, the FDA recommends that pregnant women eat eight to 12 ounces of low-mercury fish a day — but Van Horn notes the agency stops short of recommending fish oil supplements.

Likewise, the FDA also recommends that adults and children consume fish, not fish oil supplements. And, there’s “no encouraging evidence” that fish oil supplements can improve symptoms of Alzheimer’s disease or other forms of dementia, Van Horn says. Clinical trials have investigated the use of omega-3 fatty acids for depression, but with conflicting results.

Can fish oil improve my vision and eye health?

Research has shown that children whose moms had more DHA in their diets while pregnant had better vision, Van Horn says, but it’s unclear whether taking DHA in supplement form would have the same benefit. Research on whether omega-3 fatty acids can prevent or slow age-related macular degeneration, a leading cause of blindness, remain inconclusive.

Can fish oil help me lose weight?

Popular claims that fish oil can help with weight probably stem from research associating chronic inflammation with obesity, as well as the anti-inflammatory properties of omega-3 fatty acids, says Cassandra Vanderwall, a clinical nutritionist at University of Wisconsin Hospital and Clinics. “I would say those claims are false,” she notes. Indeed, research on omega-3 fatty acid supplements and weight loss is scant and inconclusive.

Can fish oil lower my risk of cancer?

Studies of whether fish oil can stave off cancer have yielded different outcomes depending on the cancer type under investigation. Human studies have suggested fish oil may lower colon cancer and breast cancer risk. But a 2013 study of men with prostate cancer associated high blood concentrations of omega-3 fatty acids with an increased risk of prostate cancer, and suggested these nutrients may actually play a role in the formation of prostate tumors.

Should I take fish oil supplements?

While it’s questionable whether fish oil supplements will improve your health, they probably won’t harm it, Vanderwall says. If you’re considering taking fish oil supplements, she and Van Horn suggest first consulting with a doctor or nutritionist. Tell them what other supplements or medications you’re taking, in case they interact negatively with fish oil. You shouldn’t take fish oil supplements if you’re also taking the blood thinner warfarin or glucocorticoid drugs like cortisone or prednisone, according to Memorial Sloan Kettering Cancer Center.

Vanderwall also suggests doing your homework on the manufacturer. While the FDA doesn’t approve supplements, look for certification from organizations like the National Sanitation Foundation (NSF) International, which tests the safety of supplements and other products.

But ideally, if you can stand the fishy flavor, you would get omega-3 fatty acids from seafood (including not only certain fish, but farmed bivalves like clams, oysters, and mussels, per NPR) instead of supplements. Besides being more environmentally sustainable, it’s also a more efficient way for your body to absorb and metabolize these fatty acids, Van Horn says. Indeed, while the research on fish oil is spotty, studies have increasingly shown the health benefits of a diet rich in fish. “A supplement can never duplicate the food,” she says.