If you've been following the media trail on fish oil lately, you've probably been tempted to forgo the smelly capsules. A systematic review of 20 studies published last week in JAMA The Journal of the American Medical Association reported that neither eating extra helpings of fish nor taking fish oil supplements reduces the risk of stroke, heart attack or death. In June a review of studies published on behalf of the Cochrane Collaboration, an independent, not-for-profit organization that promotes evidence-based decision-making, concluded that fish oil pills fail to prevent or treat cognitive decline. And a 2011 meta-analysis by Yale University researchers debunked the idea that omega-3s alleviate depression. These proclamations run counter to what we have been told about fish and fish oil for decades. So why is the consensus changing? Is it time for us to toss out our pills for good?
Not necessarily. Although it's true that early research on fish oil seemed far more promising—one 1999 trial, for instance, reported that people who took omega-3 pills were 10 percent less likely to have a heart attack, stroke or die from cardiac disease than people who did not—some researchers think that recent negative findings reveal more about us than they do about fish oil. Omega-3 pills may be beneficial for certain people but not for others, they say, and existing studies may not account for individual differences.
There's no question that polyunsaturated omega-3 fatty acids—the technical name for the good fats found in fish and fish oil—are important parts of a healthy diet. Our bodies can't make them, yet we need them to survive, as they form part of our cell membranes. Although the mechanism by which they might prevent heart disease, cognitive decline and depression isn't well understood, research suggests that they reduce blood pressure and inflammation and that they increase brain blood flow and give neurons structural strength.
And no one questions the World Health Organization's recommendation (pdf) that pregnant and nursing women should consume at least 300 milligrams of omega-3s daily to boost fetal brain development. "That [benefit] has been clearly demonstrated in trials," says Dariush Mozaffarian, a cardiologist and epidemiologist at Harvard University, who studies fish oil.
But for other adults, the health benefits of supplementing have become much harder to gauge. That's in part because many of us get lots of these good fats from our diet anyway: According to the United Nations Food and Agriculture Organization, per capita fish consumption has doubled (pdf) since 1961, and "more consumption doesn't really add much bang for your buck," Mozaffarian says. In other words, adding more omega-3s to an already omega-3–rich diet does not do much good, a fact that could help explain why recent studies have been more equivocal than studies from several decades ago, when fish was less popular. "We have no evidence from populations whose dietary intake of omega-3 fatty acids may be low and who may therefore benefit from supplementation," says Alan Dangour, head of the nutrition group at the London School of Hygiene and Tropical Medicine and co-author of the recent Cochrane review. In addition, preliminary research suggests that certain ethnic groups—such as Japanese and Italians—may benefit more from omega-3 supplements than others, perhaps in part because of how well their bodies absorb the fats.