Essential fatty acids
Linoleic and alpha-linolenic acids must come from food because the body cannot make them. They form membranes, give rise to eicosanoids, and protect skin and brain.
The essential fatty acids
| Fatty acid | Family | Status | Indian food sources |
|---|---|---|---|
| Linoleic acid (18:2) | ω-6 | Essential | Sunflower, safflower, soybean, groundnut, gingelly oils |
| Alpha-linolenic acid, ALA (18:3) | ω-3 | Essential | Flaxseed (alsi), mustard oil, soybean, walnuts, green leafy vegetables, methi seeds |
| Arachidonic acid (20:4) | ω-6 | Semi-essential: made from linoleic | Meat, egg yolk, liver |
| EPA and DHA | ω-3 | Made in small amounts from ALA | Fish (sardine, mackerel), fish oil; DHA in breast milk |
Functions
- Cell membranes: part of membrane phospholipids, keeping membranes flexible.
- Eicosanoids (hormone-like messengers): arachidonic acid and EPA form prostaglandins, thromboxanes and leukotrienes, which control inflammation, clotting and blood pressure.
- Skin: linoleic acid keeps the skin's water barrier intact.
- Brain and eyes: DHA is concentrated in the brain and retina and is needed for their growth in the fetus and infant.
- Heart: PUFA eaten in place of saturated fat lower LDL cholesterol; ω-3 fats lower blood triglycerides.
Deficiency
EFA deficiency is rare in adults. It is seen in infants fed fat-free formula, in patients on long-term fat-free tube or intravenous feeding, and with fat malabsorption. Signs: scaly dermatitis, hair loss, poor wound healing and poor growth in children. Indian textbooks link phrynoderma ('toad skin': rough, horny bumps on elbows, knees and thighs) to EFA deficiency; vitamin A deficiency can also cause it.
Omega-6 and omega-3 balance
Both families use the same enzymes to make their longer products. If the diet has far more ω-6 (for example, only sunflower or safflower oil), less ω-3 gets converted and the eicosanoids made lean towards inflammation and clotting. The simple fix: combine oils (for example groundnut with mustard) and add flaxseed, walnuts, green leafy vegetables or fish.
Indian diets usually get enough linoleic acid from cooking oils but too little ω-3. ICMR-NIN advises a combination of oils rather than a single oil, plus ω-3 foods such as flaxseed, mustard oil, greens and fish. PUFA-rich oils also supply vitamin E, which protects these fatty acids from oxidation.
5 marks: “Write a short note on essential fatty acids.” Define, name linoleic, alpha-linolenic and arachidonic acids, list functions (membranes, eicosanoids, skin, brain), deficiency signs and food sources.
2 marks: “Define essential fatty acids. Give two examples.” Fatty acids the body cannot make and must get from food: linoleic acid (ω-6) and alpha-linolenic acid (ω-3).
2 marks: “Why is arachidonic acid called semi-essential?” The body makes it from linoleic acid, so it is needed in food only when linoleic acid is short.
Two must-haves from food: LA (linoleic, ω-6) and ALA (alpha-linolenic, ω-3). Arachidonic is the 'semi' one because the body makes it from LA.