This article originally appeared on Time.com.
Doctors and health officials have long urged the public to eat more fish, since the healthy fats in fish—primarily from the omega-3 family—tend to lower risk of heart attacks and other heart problems. In fact, the most recent dietary guidelines recommend that Americans eat more fatty fish per week. (About half of Americans don’t eat any fish at all, or consume it only occasionally.)
But lately, there’s been confusion over whether the benefits of omega-3 fatty acids from food or supplements actually lead to healthier hearts and fewer cases of heart disease. For example, some studies suggest that fish oil supplements, which contain the active ingredients eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), may not lower risk of having a heart attack, but may lead to fewer fatal ones.
In a study published in the Mayo Clinic Proceedings, researchers reviewing 34 studies on EPA and DHA from food and supplements, as well as heart disease risk, found evidence of the benefits of omega-3 fats in reducing heart problems. There is a caveat, however: the study was funded by the Global Organization for EPA and DHA Omega-3s (GOED), a group of makers and marketers of fish oil products. According to the study authors, GOED did not play a role in the design or interpretation of the study results.
The analysis included gold-standard clinical trials—in which people were randomly assigned to take omega-3s or not, then followed for their heart disease outcomes—as well as population-based studies, which looked for trends among people eating or taking omega-3s and those who did not over longer periods of time. Overall, those consuming more fish oil in the population studies lowered their risk by 18%.
Among the people participating in the clinical trials, those at higher risk of developing heart disease seemed to benefit more from the fish oil. In people with high triglyceride levels, coronary heart disease risk dropped 16%, and 14% in people with high LDL cholesterol.
While the results suggest that EPA and DHA may help to lower heart disease risk, experts point out that population studies may be biased toward finding benefit, since people who take omega-3 fatty acids may also engage in healthier behaviors like exercising regularly, avoiding smoking and eating healthy diets while avoiding high sodium foods.
Ongoing clinical trials looking at the effect of omega-3 supplements on heart disease risk—and taking into account the potential effects of things like exercise and diet—may provide a more definitive answer on whether fish oil pills are really worth the money. Until then, heart experts say it’s best to stick with the natural sources by eating at least two servings of salmon, tuna or other fatty fish a week.