Fish oil has long been recommended as a supplement to help protect against heart disease, reduce cholesterol and to confer a whole host of health benefits. However, over the past few years the guidelines have changed –for example, in 2013 the British Heart Foundation changed its advice for patients taking omega-3 supplements following a heart attack, on the basis that the beneficial effect would be minimal.  Now, research published in JAMA Cardiology shows that fish oil may not have any cardioprotective effects in these individuals. 
This meta-analysis looked at data from 78,000 patients with a history of coronary heart disease, stroke or diabetes. All the patients were involved in randomised trials examining marine-derived omega-3 fatty acid supplements, placebo or no treatment. They discovered that the fish oil supplements were no better than placebo. In other words, the supplements: “did not reduce the risk of coronary heart disease deaths, nonfatal heart attacks, fatal or nonfatal strokes, revascularization procedures, or all-cause mortality among the full study population. The supplements also didn’t protect against major vascular events in any subgroups, including people with a history of heart disease, diabetes, high cholesterol, or statin use.” 
The groups authors do concede that the patient populations were ‘heavily medicated’, which may have made it difficult to fully assess any beneficial effects of fish oil supplements. Furthermore, the overall health benefits of eating oily fish as part of a balanced diet should not be discounted – the Mediterranean Diet is still recommended by the NHS, for example. 
In the meantime, two other studies – the Reduction of Cardiovascular Events with EPA–Intervention Trial (REDUCE-IT), and Statin Residual Risk Reduction with EpaNova in High Cardiovascular Risk Patients with Hypertriglyceridemia (STRENGTH) – will test high doses (4g) of fish oil supplements in patients with very high triglyceride levels and who are taking statins. These supplements have been shown to reduce triglyceride levels,  however as the study authors point out they have not been tested for heart attack, stroke or mortality. 
So, although at the currently recommended dose omega-3 fish oil supplements do not appear to protect against myocardial infarction, cardiac death or stroke, according to the recent meta-analysis mentioned above, the jury is still out on the possible benefits of higher doses in patients with high triglyceride levels and in subjects receiving treatment with statins.
The results of these prospective randomised trials are eagerly awaited. It is important to stress the fact that current guidelines recommend eating oily fish as part of a balanced diet. However, it is likely that the widespread use of powerful cardioprotective medications is making certain interventions which were shown to be effective in the past -such as fish oil supplements- redundant nowadays.