About Fish Oil

Ask the DOC

Omega-3 fatty acids, also known as fish oil, have been around for years. Last month, the Journal of the American Medical Association published the results of the STRENGTH trial, which looked at whether omega-3 fatty acids were helpful at preventing heart disease and stroke. The trial was huge with tens of thousands of participants in countries in North and South America and Asia. While the results of the trial were disappointing (they failed to show a reduction in risk of heart disease with omega-3 acids), there were some interesting tidbits of information that came out of the trial.

Omega-3 fatty acids are thought to lower triglyceride levels, slightly raise HDL (“good” cholesterol) levels, and slightly lower blood pressure. Omega-3s cannot be made in the body and help with cell growth, muscle activity, and have anti-inflammatory properties. They are derived from fatty fish such as salmon, mackerel, and trout and shellfish including mussels, oysters, and crabs. Some nuts and seeds contain a different omega-3, alpha linolenic acid (ALA).

There are different types of omega-3 fish oils and they have different properties. These types include docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and a derivative of EPA called icosapent ethyl (IPE). While it is known that people who eat dietary sources of fish oils have a lower risk of dying from heart disease, most research so far has shown that fish oils have little to no benefit in preventing heart disease. Research is ongoing to explain that apparent contradiction. While there seems to be no direct harms from taking fish oil supplements, side effects do include a fishy aftertaste, bad breath, a rash, and heartburn, nausea, or diarrhea. Also, they may interact with some medications increasing the risk of bleeding if on blood thinners, low blood pressure if on blood pressure meds, and may interfere with the functioning of contraceptives.

So far, some studies, such as the STRENGTH study, have shown no benefit from taking fish oils, while other studies, for example REDUCE-IT, have shown a positive benefit. What is becoming clearer is that the fish oil being studied is important to the possible outcome. For example, studies that used EPA and DHA had different results from others that studied IPE or ALA. Another factor in determining the outcome may be the type of placebo that is used in the study. Since most fish oils are liquids, the studies have used either liquid-filled capsules or the liquid itself and used either mineral oil or corn oil as the placebo.

Extended use of either of these oils can have its own effects on health, thereby potentially altering the outcomes of the study. The importance of the specific omega-3 formulation in achieving a beneficial reduction in heart disease risk and the degree to which the placebo may have affected the outcomes remains unresolved, accounting for seemingly opposite outcomes from similar studies. Someone once said that science can be cloudy before it becomes clear (I think it was Yogi Berra ;). Obviously, more study and research are needed, but meanwhile if you do take a fish oil supplement you can be comforted by the fact that while it may not help you, it may give you bad breath but probably won’t harm you.

Please direct questions and comments to This email address is being protected from spambots. You need JavaScript enabled to view it.

By Peter Galvin, MD

Sign up via our free email subscription service to receive notifications when new information is available.