Nutritional Role of Fatty Acids

Abstract

Saturated fatty acids and monounsaturated fatty acids (MUFA) are synthesized by the body to provide adequate levels needed for their physiological and structural functions. There are four families of polyunsaturated fatty acids (PUFA). Two are derived from palmitoleic and oleic acids, which can be formed endogenously. Linoleic acid (LA), W6, and alpha linolenic acid (ALA), W3, cannot be synthesized by humans but are required for normal growth and function of all tissues. These two fatty acids must be supplied by dietary sources and are called essential fatty acids (EFA). The four precursor fatty acids are desaturated and elongated by the same enzyme system to form long-chain PUFA. The principal products derived from LA are arachidonic acid (AA) with four double bonds (tetraene) and dihomo-gamma-linolenic acid (DHGL/DGLA), whereas products of ALA are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The major products of palmitoleic and oleic acids are 20 carbon fatty acids with three double bonds (triene). In the presence of adequate dietary amounts of EFA, tetraene products predominate in plasma. When the intakes of EFA are low, triene formation is high, and hence triene/tetraene ratio in the plasma is used to assess the index of EFA deficiency. The PUFA derived from EFA are components of cell membrane phospholipids, can influence the physicochemical characteristics of the lipid bilayer, and can result in altered cell and organ functions. Linoleic acid and its derivative gamma-linolenic acid (GLA) are specifically required in the skin to maintain the integrity of the epidermal water barrier. DHA has a role in the development of the brain and retinal functions. AA, DGLA, and EPA are precursors of eicosanoids that influence many cell processes and organ functions. In general, eicosanoids derived from AA are pro-inflammatory, while those formed from EPA and DHGL/DGLA are less inflammatory or anti-inflammatory. W3 fatty acids, and especially EPA and DHA, are associated with reduction in the risk for coronary heart disease. Some drugs can decrease the formation of eicosanoids. It is possible to modulate the fatty acid components of membrane phospholipids by dietary means, which in turn can alter the types of eicosanoids formed endogenously. Fish and fish oil supplements are rich in EPA and DHA, along with algae sources of DHA. The EFA deficiency symptoms include reduced growth, scaly dermatitis, impaired reproduction, and susceptibility to infection. There is a positive linear trend between intake of trans-fatty acids and increased risk of coronary heart disease. Small amounts of trans-fatty acids are unavoidable in an ordinary non-vegan diet because it is present in meat and dairy products. However, one can limit or reduce the quantity by eliminating products made by using hydrogenated saturated fats. There are few reports on favorable effects of conjugated fatty acids. However, more data are needed to determine their beneficial health effects.