In the chloroplasts of green leaves and in the phytoplankton in the oceans linoleic acid can be further desaturated with a third C=C double bond inserted between carbons 3 and 4, so now the first double bond is encountered starting with carbon 3 from the methyl end to form the parent compound of the n-3 polyunsaturated fatty acids, α-linolenic acid (C18:3n-3, LNA). In the bodies of fish and humans the LNA can be further desaturated and elongated to form eicosapentaenoic acid (C20:5n-3, EPA). EPA can be further elongated and desaturated to form docosahexaenoic acid (C22:6n-3, DHA). DHA is the longest and most unsaturated fatty acid normally in our diets. EPA and DHA are the two physiologically most active ingredients in fish oil.