Linoleic acid (18:2n-6) and α-linolenic acid (18:3n-3) are essential fatty acids (EFAs), meaning that they must be obtained from the diet. Indeed, they are synthesized by plants and cannot be synthesized sufficiently by the human organism [190]. However, animals can metabolize α-linolenic acid by further desaturation and elongation to yield eicosapentaenoic acid (20:5n-3; known as EPA) and docosahexaenoic acid (22:6n-3; known as DHA). It is important to note that the same enzymes are employed by omega-6 fatty acids for their metabolic pathways, which leads to the production of arachidonic acid. This means that α-linolenic acid is a competitive inhibitor of linoleic acid metabolism and vice versa [191]. However, it has been demonstrated that the conversion to EPA and DHA is generally poor in humans, with reported rates of less than 15%. Therefore, these fatty acids must be supplied with food [192]. Alfa-linolenic acid is present in plant oils, DHA and EPA are present in fish, fish oils, and krill oils.