The body can make most of the twenty or so fats that we normally consume. Only two fats are essential - omega- 6s and omega-3s, and these polyunsaturated fatty acids must be obtained from diet or from supplements. The omega-3 fatty acids include the long-chain fatty acids eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and ??-linolenic acid (ALA). These essential fats get stored as phospholipids on the cell membranes and then serve as precursors for many biological functions. Within the past 100 years, the consumption of total fat and omega-6 has increased, while the intake of omega-3s has decreased. Various authorities consider the modern increase in the consumption of omega-6 fatty acids and the vastly increased ratio of omega-6 to omega-3 ingestion to be a root cause of chronic activation of inflammatory responses.

Omega-3 fatty acids are distinguished by their molecular structure. Fats are long chains of carbon atoms. The "omega" refers to the place along the chain where the first double bond connects the carbons (see figure). Starting from the methyl end (CH3 or omega end) of the chain, the place where the first double bond is placed defines a "family" of similar fats. Omega-3s have the first double bond between the third and fourth carbon atoms. Marine animals supply mostly EPA and DHA and some plants (fl ax, canola, soy oils) provide dietary sources of ALA.

ALA from plant oils must be elongated (more carbon atoms added) and desaturated (more double-bonds between the carbons added) before this omega-3 fatty acid can be utilized for many purposes in the body. Conversion to the bioactive form is poor; only about 10% of ALA makes it to a bioactive state.

The Food and Drug Administration on September 8, 2004 gave "qualified health claim" status to EPA and DHA omega-3 fatty acids because "supportive but not conclusive research shows that consumption of EPA and DHA [n-3] fatty acids may reduce the risk of coronary heart disease." The omega-3 fatty acids also are essential for normal growth in young children. A great deal of evidence also supports roles for the omega-3 fatty acids, especially EPA and DHA, in boosting brain function and promoting cardiovascular health.