A fatty acid is a carboxylic acid having a chain of 4 to 28 carbon atoms which is either saturated or unsaturated. Fatty acids are the main components of fats, and the quality of food fats depends on the type of fatty acids that they contain.
In the human body, fatty acids are important sources of fuel because, when metabolized, they yield relatively large quantities of energy. Beside the energetic function, some fatty acids can modulate biological functions. By example, regulatory functions are mainly ascribed to polyunsaturated fatty acids (PUFAs), which are classified according to the position of the first unsaturation in the carbon chain.
Alpha-linolenic acid (ALA), the shorter omega-3 (or n-3) PUFA, cannot be synthesized by the human body, and it is therefore considered an essential fatty acid. Two longer and more unsaturated n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can be synthesised by humans from ALA. However, the capacity of synthesis is relatively low, not enough to cover the body's requirement: the conversion of ALA into EPA is estimated to be around 8-12% and may be less than 1% for ALA into DHA.
EPA and DHA, usually referred to as n-3 long-chain PUFAs (n-3 LC-PUFAs), are important components of cell membranes, precursors of bioactive molecules (eicosanoids and docosanoids), and modulators of the expression of several genes. Consequently, it is important to cover their requirement through the diet. Relatively few natural foods contain EPA and DHA in sufficient quantity to impact levels in the body. The main natural source of DHA and EPA is fish, particularly fat fish. Fish consumption is below reccommended levels in several countries.
In recent years some protective effects related to EPA and DHA have been evidenced, particularly in cardiovascular disease prevention. Considering all the scientific studies related to cardiovascular health, an intake of 250 mg per day of EPA plus DHA appears to be beneficial for cardiovascular disease primary prevention (http://www.efsa.europa.eu/en/search/doc/1461.pdf).
The metabolic syndrome is characterised by accumulation of cardiovascular risk factors, and the use of n-3 LC-PUFA could potentially benefit it. Actually, many studies indicate that the administration of EPA + DHA doses > 1 g for at least 3 months produces a significant reduction of triglycerides.