Some years ago, researchers discovered that members of the Inuit tribe, native to the Arctic, had a much lower rate of heart disease than non-natives. In time, the researchers concluded that the reason was that the Inuit diet consists mainly of fish that are high in certain types of fats.

These fish contain what scientists call “long-chain n-3 fatty acids” (including omega-3 and omega-6 fatty acids) that are polyunsaturated and improve cholesterol levels and reduce triglyceride levels in the bloodstream. These fatty acids may reduce the risk of fatal heart rhythms and may have beneficial effects on triglyceride levels and blood clotting.

Subsequently, the Physicians’ Health Study found that high blood levels of n-3 fatty acids were related to a greatly lowered risk of sudden death from heart problems. In the Nurses’ Health Study researchers found that the more frequently a woman eats fish, the lower her risk of getting heart disease or having a heart attack.

The Health Professionals’ Study revealed that eating fish at least once per month was associated with an over 40 percent lower risk of stroke. In addition, there’s now evidence that eating fatty fish also helps protect the hearts of people who already have heart disease.

One study of more than 11,000 people with heart disease found that taking a 1-gram daily supplement of n-3 polyunsaturated fatty acids (equivalent to 3.5 ounces of salmon or 7 ounces of tuna) lowered their risk of having a fatal heart problem by up to 30 percent.

In another study, British heart patients who were advised to eat two servings of oily fish a week for two years had a 29 percent lower risk of death. These studies suggest that eating fatty fish helps heart disease patients. By the way, the fish themselves do not produce these substances.

The oils are made by small marine organisms that the fish eat. They occur in varying proportions in different fish. In general, the fish that seem to have more oil have more of these fatty acids. High concentrations are found in tuna, sardines, salmon, mackerel, and herring.

But it’s likely that not all fatty fish are alike in providing these benefits. Mackerel, for example, is a fatty fish that can provide as much as 1 gram of omega-3 fatty acid with each serving. But it also contains nearly 2 grams of saturated fat. Tuna, on the other hand, has between 0.2 and 1.2 grams of omega-3 fatty acid per serving (depending on the type of tuna), but no saturated fat.

So it pays to know which fish offer the greatest benefits. How the fish is prepared also matters. Fried, processed, salted, or pickled fish typically contain ingredients, including saturated fats and high concentrations of salt, that pose a risk to heart health that outweighs any possible benefit.

Regularly consuming food that is high in saturated fats or high in salt can raise your cholesterol or your blood pressure, respectively. So when eating fish, it is best to choose nonfried fish that was not processed or prepackaged. Given these new findings, the American Heart Association now recommends that everyone eat a full serving of fish two to three times per week.

In addition, the AHA recommends that people with heart disease consume approximately 1 gram of fish-derived omega-3 fatty acids, preferably by eating fish itself, though fish-oil supplements (also called “EPA + DHA” capsules) also may be used.

What’s more, if you have a high triglyceride level in your bloodstream, the AHA recommends that you consume 2 to 4 grams of fish-derived omega-3 fatty acids in the form of EPA + DHA capsules under the supervision of your doctor. If you take capsules, you should know that they can be taken any time with meals or not.

When they dissolve in the stomach and release the oil, some people have a fishy burp. Some experts suggest that freezing the pills can eliminate this problem. Another solution is taking them at bedtime. Fish-oil capsules vary markedly in price, so you should shop around.

And it is best to choose a supplement with an EPA/DHA ratio between 2:1 and 1:2. Some people are concerned about mercury and other pollutants in fish. It is true that the FDA has issued an advisory that is directed at reducing mercury exposure for women who may become pregnant, pregnant women, nursing mothers, and young children.

The advisory states that these groups should avoid shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury. It also expresses a concern about albacore tuna, suggesting that the above groups eat no more than one serving a week.

The advisory acknowledges that there are many benefits to eating fish and that it is an important component of a balanced diet. For patients with heart disease, the benefits of eating fish likely far outweigh any concern about mercury or other pollutants. Also, fish-oil capsules do not contain any mercury.

Some people also wonder whether it is better to eat salmon from the wild or from fish farms. Both types of fish are good sources of these fatty acids. A recent report raised some concerns about contaminants in fish from farms. The amount is very small and the benefits of eating the fish seems to far outweigh any concerns.