Omega-3 (and omega-6) fatty acids are part of a group classified as "essential" fatty acids. The human body cannot manufacturer them, but needs them. Nutrition experts believe they help prevent or lessen the effects of various ailments, including heart disease, depression, and swollen joints. They are best obtained from omega-3 rich foods, including fatty fish like mackerel, salmon, trout, and tuna. Good plant sources include flaxseed and walnuts. Fish-oil supplements are also widely available.