Lipids: Classification, Functions, Metabolism, and Dietary Recommendations
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This presentation offers a comprehensive overview of lipids, covering their classification, chemical composition, and vital roles in the human body and diet. It details the digestion, absorption, transport, and metabolism of fats, with special emphasis on essential fatty acids, sources, and recommended dietary allowances (RDA). The impact of dietary fat on coronary heart disease and current recommendations for healthy fat consumption are also discussed. Ideal for students and professionals in nutrition, dietetics, food science, and health sciences.
Lipids: Classification, Functions, Metabolism, and Dietary Recommendations
- 2. CONTENTS :- • Classification • Chemical composition • Fats in body • Fats in Food • Functions of lipids • Digestion and Absorption • Transport and Metabolism • Essential fatty acids • Recommended Dietary Allowance • Sources • Dietary Fat and Coronary Heart Disease • Recommendation on Fat components of Diet.
- 3. INTRODUCTION Lipids are a group of molecules that include fats, oils, waxes, and certain vitamins. • They do not dissolve in water, but they dissolve in oils and alcohol. • Lipids are important because: • They store energy (more than carbohydrates). • They build parts of your body, like cell membranes.
- 4. TERMINOLOGY :- FATTY ACID • A fatty acid is like a long chain made of carbon (C) and hydrogen (H) atoms. • One end of the chain has a special group called carboxyl group (–COOH). Think of a fatty acid like a train: • The train body = carbon and hydrogen atoms linked together • The engine = carboxyl group (–COOH) ESTER • When fatty acids react with an alcohol (like glycerol), they join together and form a new bond called an ester bond. • Simple example: • Fatty acid + Glycerol Forms → Fat (Triglyceride) + Water • So, ester = the link that connects fatty acids and glycerol.
- 5. MEDIUM CHAIN TRIGLYCERIDES (MCTS) • Medium Chain = Carbon chain length of 10–14 carbons. • They are easier to digest than long-chain fats. • Used in patients who have trouble digesting fat (like in diarrhea, malabsorption, or surgery). • Sources: Coconut oil, palm kernel oil. PHOSPHOLIPIDS • Special lipids with a water-loving (polar) head and fat-loving (non-polar) tail. • They make up the membranes of your cells. • Act like a wall that lets some things enter the cell and blocks others. Example: Lecithin in egg yolk. SATURATED FATTY ACID: • All carbon atoms are connected by single bonds (–). • No double bonds. • Example: Butter, ghee. • Saturated = "full" with hydrogen atoms.
- 6. UNSATURATED FATTY ACID: • Some carbon atoms are connected by double bonds (=). • Example: Olive oil, sunflower oil. • Double bonds = "space" left for more hydrogen. TRIGLYCERIDE • A triglyceride is the most common type of fat found in your body and in food. • It is made of two parts: • 1 glycerol molecule (this is like the "backbone") • 3 fatty acid chains (these are like the "tails" hanging from the backbone) So, tri- means three (three fatty acids). 04/29/2025 6
- 7. CLASSIFICATION OF LIPIDS : - Lipids are broadly classified into: • Simple Lipids: Esters of fatty acids with alcohols. • Fats (triglycerides): Esters of fatty acids with glycerol. • Waxes: Esters of fatty acids with higher molecular weight alcohols (e.g., beeswax). • Compound Lipids: Contain additional groups besides fatty acids and alcohol. • Phospholipids: Contain phosphate groups (e.g., lecithin). • Glycolipids: Contain carbohydrate groups. • Lipoproteins: Lipid-protein complexes important in lipid transport. • Derived Lipids: Substances derived from hydrolysis of simple and compound lipids. • Includes fatty acids, glycerol, sterols (e.g., cholesterol), and fat-soluble vitamins. 04/29/2025 7
- 8. 04/29/2025 8 Type What It Means Example Simple lipids Just fatty acids + alcohol Fats, oils, waxes Compound lipids Fatty acids + other groups (like phosphorus) Phospholipids, glycolipids Derived lipids From breakdown of simple or compound lipids Fatty acids, cholesterol
- 9. Chemical Composition • Lipids are composed mainly of carbon (C), hydrogen (H), and oxygen (O), with a lower proportion of oxygen compared to carbohydrates. • Basic units: • Fatty acids: Can be saturated (no double bonds) or unsaturated (one or more double bonds). • Glycerol: A 3-carbon alcohol. • Triglycerides are formed when three fatty acids esterify with one glycerol molecule. • Phospholipids consist of two fatty acids, glycerol, a phosphate group, and a nitrogen- containing molecule. 04/29/2025 9
- 10. Fats in Body • In the human body, fats are primarily stored as triglycerides in adipose tissue. • Functions: • Provide a major energy reserve. • Serve as insulation to conserve body heat. • Act as a cushion protecting internal organs (kidney, heart, etc.). • Phospholipids and cholesterol are integral components of cell membranes. • Cholesterol acts as a precursor for the synthesis of steroid hormones, vitamin D, and bile acids. 04/29/2025 10
- 11. Fats in Food • Visible fats: Ghee, butter, oils, margarine. • Invisible fats: Found within foods like milk, cereals, legumes, nuts, meat, fish. • Animal fats (butter, cream, lard) are rich in saturated fats. • Vegetable oils (except coconut oil and palm oil) are rich in unsaturated fats. • Fat content varies depending on the type of food and preparation methods. 04/29/2025 11
- 12. Functions of Lipids Energy Source • Lipids are the richest source of energy, providing approximately 9 kcal per gram, which is more than double the energy provided by carbohydrates (4 kcal/g) and proteins (4 kcal/g). • During rest and low-intensity activities, especially in a fasting state, lipids are the primary fuel source. • In times of starvation, body fat stores can supply energy for several weeks. Structural Component • Lipids are critical building blocks of cell membranes. • Phospholipids form the lipid bilayer structure of all cell membranes, ensuring: • Membrane fluidity (important for cell function). • Selective permeability (controls the movement of substances in and out of cells). • Cholesterol is embedded between phospholipids to stabilize membrane structure, especially at varying temperatures. 04/29/2025 12
- 13. Carrier and Absorption of Fat-Soluble Vitamins • Lipids are essential for the absorption, transport, and storage of fat-soluble vitamins: A, D, E, and K. • Without sufficient dietary fat, these vitamins cannot be absorbed properly in the intestine, leading to deficiencies even if vitamin intake is adequate. • Fats help in micelle formation in the intestine, aiding the solubilization and absorption of these vitamins. Satiety and Palatability • Fats enhance the taste, aroma, and texture of foods, making them more appealing and flavorful. • Dietary fat delays gastric emptying, meaning food stays longer in the stomach, which contributes to a feeling of fullness (satiety) after meals. • This function helps regulate appetite and can prevent overeating when fats are consumed in appropriate amounts. 04/29/2025 13
- 14. Precursor for Biologically Active Compounds • Certain lipids serve as precursors for important signaling molecules: • Eicosanoids (such as prostaglandins, thromboxanes, and leukotrienes) are synthesized from polyunsaturated fatty acids (PUFAs) like arachidonic acid and eicosapentaenoic acid. • These compounds: • Regulate inflammation, blood clotting, vascular tone, and immune responses. • Play roles in reproductive function and gastrointestinal activities. • Cholesterol is also a precursor for steroid hormones (like cortisol, aldosterone, estrogen, testosterone) and bile acids needed for fat digestion. 04/29/2025 14
- 15. Insulation and Protection • Adipose tissue (fat tissue) acts as a thermal insulator, helping to maintain body temperature by preventing heat loss. • Fat pads around organs (e.g., kidneys, heart, intestines) serve as mechanical shock absorbers, protecting these delicate structures from injury and trauma. • Subcutaneous fat provides cushioning and contributes to the body's shape and contour. Reservoir for Essential Fatty Acids • Stored fats serve as a reservoir of essential fatty acids like linoleic and alpha-linolenic acids. • These fatty acids are vital for growth, skin health, and brain development and are released into circulation when needed. Regulation of Body Functions • Lipids help regulate important body functions: • Blood pressure (via prostaglandins). • Immune function. • Nervous system development — especially myelination of nerves which speeds up nerve impulse transmission. 04/29/2025 15
- 16. Digestion and Absorption • Begins in the stomach with gastric lipase but primarily occurs in the small intestine. • Bile salts emulsify fat into smaller droplets (micelles). • Pancreatic lipase hydrolyzes triglycerides into monoglycerides and free fatty acids. • Micelles transport lipids to intestinal mucosa, where absorption occurs. • Inside enterocytes, triglycerides are re-synthesized and packed into chylomicrons. • Chylomicrons enter the lymphatic system and then the bloodstream for distribution. 04/29/2025 16
- 17. Transport and Metabolism 04/29/2025 17 Lipoproteins facilitate lipid transport: • Chylomicrons: Transport dietary triglycerides from intestine to tissues. • VLDL (Very Low-Density Lipoprotein): Transports endogenous triglycerides from liver to tissues. • LDL (Low-Density Lipoprotein): Delivers cholesterol to cells; elevated LDL increases cardiovascular risk. • HDL (High-Density Lipoprotein): Collects cholesterol from tissues and returns it to the liver (reverse cholesterol transport). Fatty acid metabolism: • β-oxidation: Fatty acids are broken down in mitochondria to generate ATP. • Ketogenesis: During fasting, fatty acids are converted to ketone bodies in the liver.
- 18. Essential Fatty Acids (EFAs) • Linoleic acid (omega-6) and alpha- linolenic acid (omega-3) are EFAs. • Must be obtained from the diet because the body cannot synthesize them. • EFAs are important for: • Formation of cell membranes. • Synthesis of eicosanoids (inflammatory mediators). • Proper growth, skin integrity, neurological function, and immune function. • Deficiency symptoms include scaly dermatitis, poor wound healing, and growth retardation. 04/29/2025 18
- 19. Recommended Dietary Allowance (RDA) • Total fat intake: 20–35% of total daily energy intake. • Saturated fat: Should be less than 10% of total energy. • Trans fats: Should be kept below 1% of total energy. • PUFAs: 6–11% of total energy intake. • Balanced intake of omega-6 and omega-3 fatty acids is emphasized for optimal health. Sources • Animal sources: Butter, cheese, ghee, meat, fish oils, eggs. • Plant sources: Vegetable oils (olive oil, groundnut oil, sunflower oil), nuts (almonds, walnuts), seeds (flaxseed, chia seeds), avocados. • Sources of omega-3 fatty acids: Fish (salmon, mackerel), flaxseeds, chia seeds, walnuts. • Sources of omega-6 fatty acids: Sunflower oil, corn oil, soybean oil. 04/29/2025 19
- 20. Dietary Fat and Coronary Heart Disease (CHD) • High intake of saturated fats and trans fats increases LDL cholesterol, promoting atherosclerosis and CHD. • PUFAs and MUFAs lower LDL and are protective against heart disease. • Omega-3 fatty acids help reduce triglycerides, blood pressure, and inflammation. • Replacing saturated fats with unsaturated fats and avoiding trans fats significantly lowers CHD risk. 04/29/2025 20
- 21. Recommendation on Fat Components of Diet • Limit saturated fat to less than 10% of total calories. • Keep trans fats as low as possible (<1%). • Increase intake of unsaturated fats — both MUFAs and PUFAs. • Include rich sources of omega-3 fatty acids like fatty fish, flaxseeds. • Focus on a balanced diet with both visible and invisible fats accounted for. • Emphasize whole foods over processed foods with hidden harmful fats. 04/29/2025 21
- 22. ICMR-NIN 2024: Recommende d Dietary Allowance for Lipids 1. Total Fat Intake • Adults: 20–30% of total energy intake • For a 2,000 kcal/day diet: 44–66 grams/day 2. Saturated Fatty Acids (SFA) • Should be less than 10% of total energy intake • For a 2,000 kcal/day diet: less than 22 grams/day 3. Trans Fatty Acids Should be as low as possible, ideally less than 1% of total energy intake • For a 2,000 kcal/day diet: less than 2 grams/day • 4. Polyunsaturated Fatty Acids (PUFA) • Recommended to be 6–10% of total energy intakeFor a 2,000 kcal/day diet: 13–22 grams/day 04/29/2025 22
- 23. 5. Monounsaturated Fatty Acids (MUFA) • Recommended to be 10–12% of total energy intake • For a 2,000 kcal/day diet: 22–26 grams/day 6. Essential Fatty Acids • Linoleic Acid (Omega-6) • 4–6% of total energy intake • For a 2,000 kcal/day diet: 9–13 grams/day • Alpha-Linolenic Acid (Omega-3) • 0.5–1% of total energy intake • For a 2,000 kcal/day diet: 1–2 grams/day 04/29/2025 23