chap 5

Lipids: Organic compounds that are insoluble in water but soluble in organic solvents like ether and chloroform. They include fats, oils, waxes, phospholipids, and sterols.

Three classes of lipids & differences between them:

  1. Triglycerides: Composed of glycerol and three fatty acids. Main storage form of fat in the body and a major component of dietary fat.

  2. Phospholipids: Contain a phosphate group in addition to fatty acids. Important in cell membrane structure and function, enabling selective permeability.

  3. Sterols: Have a specific ring structure. Cholesterol is a prominent example, serving as a precursor for steroid hormones and a component of cell membranes.

Why is fat important? Fat is crucial for several physiological functions:

  • It provides a concentrated source of energy.

  • Fat serves as insulation, helping to maintain body temperature.

  • It protects organs by providing a cushioning effect.

  • Fat aids in the absorption of fat-soluble vitamins (A, D, E, and K).

Usefulness of fat in the body: Fat plays vital roles in:

  • Providing energy during prolonged activities.

  • Cushioning and protecting organs.

  • Insulating the body to maintain temperature.

  • Assisting in the absorption of fat-soluble vitamins.

  • Providing essential fatty acids necessary for cell function.

Satiety: Fat contributes to feelings of fullness or satiety after a meal, slowing down digestion and promoting a sense of satisfaction.

Phospholipids: Phospholipids are a type of lipid that forms the structural basis of cell membranes. They have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails, enabling them to form a lipid bilayer that surrounds cells.

Sterols: Sterols are a type of lipid with a specific ring structure. Cholesterol is the most well-known sterol, serving as a precursor for steroid hormones and a structural component of cell membranes.

Lipoproteins (HDL, LDL, etc.): Lipoproteins are complex particles that transport lipids (such as cholesterol and triglycerides) in the bloodstream. High-density lipoprotein (HDL) is considered "good" cholesterol as it helps remove cholesterol from the bloodstream, while low-density lipoprotein (LDL) is considered "bad" cholesterol as it can contribute to plaque buildup in arteries.

Triglyceride: Triglycerides are the most common type of fat found in the body and in food. They consist of glycerol and three fatty acids and serve as a storage form of energy.

Saturated/unsaturated fats: Saturated fats have no double bonds between carbon atoms and are typically solid at room temperature, while unsaturated fats have one or more double bonds and are usually liquid at room temperature.

Essential fatty acids: Essential fatty acids, such as omega-3 and omega-6 fatty acids, cannot be synthesized by the body and must be obtained from the diet. They are critical for various physiological functions, including brain function, inflammation regulation, and cardiovascular health.

Emulsification: Emulsification is the process of breaking down large fat globules into smaller droplets, increasing the surface area for digestive enzymes to work on. This process is facilitated by bile acids produced by the liver and stored in the gallbladder.

Fat digestion: Fat digestion begins in the mouth with lingual lipase and continues in the stomach and small intestine with the action of lipases and bile. Emulsification and enzymatic breakdown ultimately result in the absorption of fatty acids and monoglycerides into the bloodstream.

Omega-3 & omega-6 fatty acids: Omega-3 and omega-6 fatty acids are polyunsaturated fatty acids that are essential for health. They play crucial roles in brain function, reducing inflammation, and supporting heart health. Sources include fatty fish, flaxseeds, walnuts, and vegetable oils.

Trans fats: Trans fats are unsaturated fats with trans double bonds, often formed through the process of hydrogenation. They have been linked to an increased risk of heart disease and should be minimized in the diet.

Cholesterol and types: Cholesterol is a type of sterol found in animal products and synthesized by the liver. It plays essential roles in cell membrane structure and hormone synthesis. Types include LDL (low-density lipoprotein) and HDL (high-density lipoprotein), which transport cholesterol in the bloodstream.

Hydrogenation: Hydrogenation is a chemical process that converts unsaturated fats into saturated fats by adding hydrogen atoms. This process is often used to solidify liquid oils and increase the shelf life of food products but can lead to the formation of trans fats.