Omega-3 fatty acids are found in fatty layers of cold-water fish and shellfish, plant and nut oils, English walnuts, flaxseed, algae oils, and fortified foods. You can also get omega-3s as supplements. Food and supplement sources of these fatty acids differ in the forms and amounts they contain.
Long-chain omega-3 fatty acids are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These are plentiful in fish and shellfish. Algae often provides only DHA.
Short-chain omega-3 fatty acids are ALA (alpha-linolenic acid). These are found in plants, such as flaxseed. Though beneficial, ALA omega-3 fatty acids have less potent health benefits than EPA and DHA. You’d have to eat a lot to gain the same benefits as you do from fish.
In addition to omega-3s, fish is high in protein, vitamins, and minerals. And, it’s low in saturated fat. Studies suggest that omega-3s may provide some benefits to a wide range of diseases: cancer, asthma, depression, cardiovascular disease, ADHD, and autoimmune diseases, such as rheumatoid arthritis.