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 omega-3 fatty acids differ structurally from omega-6 fatty acids. Evidence from studies show that omega-3 fatty acids may reduce the chances of getting atherosclerosis, rheumatoid arthritis, migraine headaches, and other heart and inflammatory diseases. A study suggests that fish oil can be very helpful for bipolar disease, more commonly known as manic-depressive disorder. More research is needed, but this appears to be a potential breakthrough for this devastating illness, whose conventional treatments cause many side effects.