Overview
This lecture covers Chapter 5 on lipids, explaining their roles in the body and food, the three main classes, metabolism, and nutrition recommendations.
Functions and Usefulness of Lipids
- Lipids are insoluble in water and serve as essential macronutrients.
- Provide 80-90% of the body's energy at rest and are the chief form of stored energy.
- Offer padding and insulation for organs and help protect against cold.
- Act as raw materials for cell membranes, vitamin D, sex hormones, and bile.
- In food, lipids supply 9 calories/gram, aid absorption of fat-soluble vitamins (A, D, E, K), increase satiety, and contribute to flavor and texture.
Classes of Lipids
- Three major classes: triglycerides, phospholipids, and sterols.
- Triglycerides: main form in body and food; made from three fatty acids and glycerol.
- Saturated fatty acids have no double bonds, solid at room temp, mostly animal sources.
- Unsaturated fatty acids (mono- and polyunsaturated) have one or more double bonds, liquid at room temp, mainly plant sources.
- Phospholipids: two fatty acids, phosphate group, and glycerol; function as emulsifiers and cell membrane components.
- Sterols: carbon ring structures; basis for cholesterol, vitamin D, and sex hormones.
Fat Digestion, Absorption, and Storage
- Fat digestion starts minimally in mouth and stomach, mainly occurs in the small intestine.
- Bile emulsifies fats; pancreatic enzymes break down triglycerides to fatty acids.
- Short/medium-chain fatty acids enter blood directly; long-chain are packaged as chylomicrons and enter the lymph system.
- Chylomicrons (lipoproteins) carry lipids in blood; triglycerides are stored in adipose tissue until needed for energy.
Nutrition Recommendations for Fat
- AMDR for fat: 20-35% of total calories; saturated fat should be ≤10% of total calories.
- American Heart Association recommends ≤5-6% saturated fat for those with high cholesterol.
- No current dietary recommendations for trans fat or cholesterol.
- Saturated fat raises LDL ("bad") cholesterol, increasing cardiovascular disease risk.
- LDL delivers cholesterol to cells; HDL ("good" cholesterol) removes excess cholesterol.
- Lower LDL by reducing saturated fat, replacing with unsaturated fat, and increasing fiber.
- Raise HDL with exercise and not smoking; diet alone has limited effect.
Key Terms & Definitions
- Lipid — fat or fat-like substance, insoluble in water.
- Triglyceride — main lipid form in body/food; three fatty acids + glycerol.
- Phospholipid — lipid with two fatty acids and phosphate; key in cell membranes and emulsification.
- Sterol — class of lipid, includes cholesterol and hormones.
- Chylomicron — lipoprotein that transports lipids from intestines.
- LDL (Low-Density Lipoprotein) — "bad" cholesterol, raises CVD risk.
- HDL (High-Density Lipoprotein) — "good" cholesterol, protective.
Action Items / Next Steps
- Review Chapter 5 recommended sections not covered in this lecture.