I read the Harvard Health Letter for March 2011 and then found a series of related medical articles and an interesting editorial. Let's start with the Harvard publication.It mentions four trials of fish oil supplements in people with pre-existing heart disease. None of those showed a positive effect in patients who are also on modern drug therapies.
Above the brief summary box was an longer commentary quoting Dr. Robert Eckel, the former president of the American Heart Association. He said "If you have heart disease, taking fish oil doesn't seem to replace eating fish." He also wrote the editorial I read in the journal Circulation. Dr. Eckel, who is on the staff of the Department of Medicine in the University of Colorado's medical school (down the road about 65 miles from me), carefully analyzed the four studies and concludes that prior evidence showing diets that include fish make sense, but taking fish oil supplements after you've had a heart attack doesn't.
A Mayo Clinic position paper I found online recommends eating one to two servings of fish a week and notes that fatty fishes, like salmon, herring and even tuna, are higher in the omega-3 fatty acids that may help. Talapia (which I've eaten twice this week) and catfish, are less likely to be heart healthy and any fish that's deep-fat fried may be bad for you.
What about those of us who haven't had clinical heart disease (yet)? Even the Harvard letter says fish oil may be okay for preventive therapy. But I'm not able to find good solid data to support this.
It seems true that populations that eat more fish, like the Inuit and some of the long-term participants in the Nurses' Health Study, were less likely to have a variety of severe heart disease issues (heart attacks, sudden death, heart rhythm problems). The unresolved question is whether they also had better health habits or genetics or other reasons for their diminished risk.
So from my point of view I'll continue taking my twice-a-day fish oil capsule. It's one that is third-party tested for heavy metals, PCBs and dioxins and the relative low dose of omega-3s (270 mg of EPA, 180 mg of DHA, 115 mg of other omega-3s) plus the addition of small doses of omega-9s and 6s seems more likely to help than harm
But I'm going to keep on eating fish, try some fatty fishes and watch the literature.