SN3 SHORT NOTE 5M ★ High-yield

Define essential fatty acids. Give their sources, functions and the features of deficiency.

Biochemistry · 1st Professional — Pre-Clinical

Essential fatty acids = polyunsaturated fatty acids that cannot be synthesised by man and must be supplied in the diet.

Man lacks desaturases beyond carbon 9, so a double bond cannot be introduced at position ω-3 or ω-6

Fatty acid	Carbons : double bonds	Family	Source
Linoleic acid	18 : 2	ω-6	Sunflower, safflower, corn, soybean oil
α-Linolenic acid	18 : 3	ω-3	Flaxseed, mustard, walnut, soybean oil
Arachidonic acid	20 : 4	ω-6	Semi-essential — made from linoleic acid
EPA and DHA	20:5 and 22:6	ω-3	Fish oil; made poorly from α-linolenic acid

Precursors of eicosanoids — prostaglandins, thromboxanes and leukotrienes, all derived from arachidonic acid
Membrane structure and fluidity; phospholipid components
DHA is a major structural lipid of the retina and brain — critical in fetal and infant development
Lower plasma cholesterol and LDL; ω-3 lowers triglyceride and has antithrombotic and anti-inflammatory effects
Maintain the integrity of skin and the epidermal water barrier
Needed for normal reproduction and growth

Scaly dermatitis and increased transepidermal water loss
Poor wound healing, hair loss
Growth retardation in children; thrombocytopenia
Fatty liver
Rare on a normal diet; seen in prolonged fat-free parenteral nutrition and severe fat malabsorption

Both families compete for the same desaturase and elongase enzymes
ω-6 derived eicosanoids are broadly pro-inflammatory and pro-aggregatory; ω-3 derived ones are less so
A ratio of about 5:1 to 10:1 is recommended; the modern diet is often 15–20:1 because of the heavy use of ω-6 rich seed oils

Fish oil (ω-3) reduces plasma triglyceride substantially and is used in severe hypertriglyceridaemia
Infant formula is fortified with DHA, since breast milk supplies it and it is needed for retinal and neural development
Trans fats, produced by partial hydrogenation of vegetable oils, raise LDL and lower HDL — the worst combination; now restricted by law in many countries including India
Prolonged parenteral nutrition requires intravenous lipid emulsion to prevent essential fatty acid deficiency, which can appear within 2–4 weeks

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