HEALTH EFFECTS OF DIETARY UNSATURATED FATTY ACIDS

INTRODUCTION :

Fatty acids are long hydrocarbon chains with a methyl group at one end (the omega or n- end) and an acid group at the other. Unsaturated fatty acids are hydrocarbon chains containing at least one carbon–carbon double bond; monounsaturated fatty acids (MUFAs) contain one double bond, polyunsaturated fatty acids (PUFAs) contain many double bonds. Fat slows down the digestion of foods, thus contributing to meal satiety. Dietary fat aids in the absorption of the fat-soluble vitamins. Specific fatty acids have important structural, biochemical, and regulatory functions that are required for optimal tissue function, growth, and repair.

Fat is the most energy dense of all the macronutrients with 1g providing 9kcal. However, the constituent parts of fat, fatty acids, are required by the body for many other functions than as simply an energy source and there is an increasing awareness of the potential health benefits of specific types of fatty acids. Fat is found in most food groups and foods containing fat generally provide a range of different fatty acids, both saturated and unsaturated fatty acids. In humans, the essential fatty acids are the omega 3 polyunsaturated fatty acid α-linolenic acid(ALA) and the omega 6 polyunsaturated fatty acid linoleic acid (LA). Docosahexaenoic acid (DHA) is an omega-3 (n-3) long-chain (LC) polyunsaturated fatty acid (PUFA) that is a primary structural component of the human brain, testes and retina. It is derived from LA and arachidonic acid (AA)

Eicosanoids Synthesis :

Linoleic acid and α-linolenic acid are substrates for the synthesis of physiological regulators called eicosanoids. Eicosanoids include prostaglandins, prostacyclins, thromboxanes, and leukotrienes. For each, there are two or three separate series. These are potent mediators of many biochemical processes and play key roles in the regulation of blood clots, blood pressure, blood lipid levels, immune function, inflammation, pain and fever, and reproduction. The omega-6 eicosanoids (derived from LA) are generally pro-inflammatory. Consuming large amount of linoleic acid increases the quantity of arachidonic acid(AA) in cell membranes. Upon activation, in a variety of cells, arachidonic acid is converted to eicosanoids of the 2 series and leukotrienes of the 4 series. However, dietary α- linolenic acid is converted to Eicosapentaenoic acid (EPA) in the membrane, and when cells are activated, EPA is converted to eicosanoids of the 3 series and leukotrienes of the 5 series.

Sources of dietary unsaturated fatty acids :

A good dietary source useful for increasing n3 fatty acid consumption is a greater consumption of vegetable derived n-3 fatty acids. There are only three major commercial sources that have significant amounts of ALA: Linum usitatissimum, linseed or flaxseed oil (53% ALA); Brassica spp. Canola or rapeseed oil (9% ALA) and Glycine max, soybean oil (7% ALA) [1]. Perilla oil, Perilla frutescens, also contains a high percentage in ALA (approx. 60%) although its consumption is restricted to Asia, In plants, ALA is found in leaves, mainly in glycolipids, and as tri acyl glycerol (TAG) in certain seed oils (rapeseed, flaxseed, perilla seed, chia seed), beans (soybeans, navy beans) and nuts (walnuts).

Etiology of primary and secondary essential fatty acid deficiency
in human beings :

	Chronic malnutrition, especially in children
	Long-term fat-free total parental nutrition (TPN)
	Various fat malabsorption conditions
	Sjogren–Larsson syndrome
	Acrodermatitis enteropathica
	End-stage liver disease

Clinical manifestations of essential fatty acid deficiency in human
beings :

	Dermatitis; dry, scaly skin; impetigo; eczema; generalized erythema
	Coarse, sparse hair
	Increased frequency of stools
	Decreased growth rate
	Cellular hyperproliferation in skin, alimentary tract, and urinary tract
	Possible immune impairment
	Slow wound repair
	Slower early learning behaviour
	Mental retardation in human genetic defects involving desaturases and elongases