Control of Fatty Acid Intake and the Role of Essential Fatty Acids in Cognitive Function and Neurological Disorders

Abstract

A fatty acid is a carboxylic acid often with a long unbranched aliphatic chain and is divided into two categories based on structural and chemical properties: (1) saturated and (2) unsaturated. Saturated fatty acids do not contain any double bonds or other functional groups along the chain. Unsaturated fatty acids contain at least one pair of carbon atoms linked by a double bond enabling the addition of other atoms to these carbons. Distinction between the two is simply that saturated fatty acids are usually solid at room temperature whereas unsaturated fatty acids are liquid. Unsaturated fatty acids can be further divided into monounsaturated (which contains only one double bond) or polyunsaturated fatty acids (PUFAs), which contain more than one double bond. PUFAs are further grouped based either on the location of the double bonds and/or according to the chain length. An omega (ω ) notation indicates the number of carbon atoms from the methyl end to the first double bond. Omega-3 (ω – 3 or n – 3) and Omega-6 (ω – 6 or n – 6) are two well-known fatty acids that are termed “essential fatty acids” (EFA). Such EFA are obtained from diet since they cannot be manufactured by cells (double bonds can be introduced into all positions of the fatty acid chain except the n – 3 and n – 6 positions). α-Linolenic acid (ALA) is an ω – 3 fatty acid that is converted to eicosapentaenoic acid (EPA) and subsequently from EPA to docosapentaenoic acid (DPA) and then to docosahexanoic acid (DHA). Linoleic acid (LA) is the parent fatty acid for ω – 6 class of fatty acids. LA is converted to γ-linoleic acid (GLA) which through subsequent conversions results in the formation of arachidonic acid (AA) and is a precursor for several classes of eicosanoids. In the nervous system, cell membranes contain relatively high concentration of PUFAs, such as docosahexaenoic acid (DHA) (Stillwell and Wassall, 2003).In this review we provide a synthesis of evidence concerning the neural and hormonal control on food intake with a special emphasis on long-chain fatty acids. Fatty acids act on the central nervous system (CNS) as important physiological regulators of energy metabolism and overall energy homeostasis. In addition, we will examine evidence on key neural structures and systems influenced by fatty acids that are involved in feeding behavior. Lastly, we will review evidence on the role of EFA in preventing cognitive decline as well in neurological disorders.