By Biplab Das
Introduction
Ancient hunter-gatherer populations subsisted on a diet much lower in saturated fatty acids than is today’s diet. The ancient diet contained small and roughly equal amounts of two types of polyunsaturated fatty acids (PUFAs) – linoleic acid (LA) and alpha-linolenic acid (ALA) with lower amounts of trans fatty acids. The current Western diet is very high in n-6 (Omega-6) fatty acids (ratio of n-6 to n-3 fatty acids is 20-30:1). Decrease in fish consumption coupled with industrial production of animal feeds rich in grains containing n-6 fatty acids is leading to production of meat rich in n-6 and poor in n-3 (Omega-3) fatty acids.
Even cultivated vegetables contain fewer n-3 fatty acids than do plants in the wild. Modern agriculture driven by the goal to produce is suggested to have decreased n-3 fatty acid content in many foods: green leafy vegetables, animal meats, eggs and even fish. These dietary composition alterations, deficiencies and other environmental changes are contributing to diet-related diseases like cardiovascular disease (CVD), brain disorders and other diseases.
Essential Fatty Acid Metabolism and Function
Linoleic acid (LA) and alpha-linolenic acid (ALA), the parent essential fatty acids (EFA), cannot be synthesized in the human body and diet is the only source of them. After ingestion, both linoleic acid (LA) and alpha-linolenic acid (ALA) are converted into long-chain metabolites known as long-chain polyunsaturated fatty acids (LCP) through chain elongation, desaturation and chain-shortening. The most important long-chain polyunsaturated fatty acids of the (n-6) fatty acid series is arachidonic acid (AA). Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the major long-chain polyunsaturated fatty acids of the (n-3) fatty acid series. Long-chain polyunsaturated fatty acids may also be derived from diet – AA from meat and EPA and DHA from fish.
Brain and retina are rich in AA and DHA, which are important building blocks of structural lipids. Long-chain polyunsaturated fatty acids in phospholipids contribute to membrane properties like permeability, fluidity and flexibility. For instance, DHA in retina and postsynaptic membranes is crucial for adequate functioning of embedded proteins like rhodopsin for vision and postsynaptic receptors (protein molecules on the nerve cell membrane) for transmission of nerve impulses across the nerve cells. AA, EPA and dihomo-gamma-linolenic acid (DGLA of omega-6 series) give rise to highly potent regulatory hormones collectively known as eicosanoids. These short-lived chemicals play vital roles in inflammatory reactions, blood pressure control and platelet (a type of blood cell) aggregation. In recent years, polyunsaturated fatty acids (PUFA), long-chain polyunsaturated fatty acids and their derivatives are getting attention from researchers, as these chemicals are believed to modulate the expressions of genes.