Fish oil is probably the most important dietary source of omega‑3 fatty acids, which are vital nutrients. Omega‑3 fatty acids are one type of essential fatty acids, special fats that the body needs as much as it needs vitamins. Much of the research into the potential therapeutic benefits of omega‑3 fatty acids began when studies of the Inuit people found that, although their diets contain an enormous amount of fat from fish, seals, and whales, they seldom suffer heart attacks or develop rheumatoid arthritis; this is presumably because those sources of fat are very high in omega‑3 fatty acids.

These fatty acids reduce inflammation, protect against the abnormal clotting associated with heart attacks. These omega‑3 fatty acids differ structurally from omega‑6 fatty acids.

We do know that fish oil can lower serum triglycerides. Like cholesterol, triglycerides are a type of fat in the blood that tends to damage the arteries, leading to heart disease. Reducing triglyceride levels should help prevent heart disease to some extent. Fish oil also appears to modestly raise the levels of HDL (“good”) cholesterol.