Fish oil is a commonly used fatty acid supplement because it is a source of omega-3 fatty acids. Fatty acids are strings of carbon atoms, having a range of lengths. If links are all single (C-C), then the fatty acid is called saturated; with one double bond (C=C), it is called monounsaturated; if there are two or more double bonds (C=C=C), it is called polyunsaturated. Only two fatty acids, both polyunsaturated, are considered essential to be obtained from the diet, as the others are synthesized in the body. The "essential" fatty acids are alpha-linolenic acid (ALA), an omega-3 fatty acid, and linoleic acid (LA), an omega-6 fatty acid. ALA can be elongated in the body to create other omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).