NTR 306: Fundamentals of Nutrition - Chapter 5: Lipids Study Notes
Fundamentals of Nutrition - Chapter 5: Lipids
Introduction to Dietary Fat
InstaPoll Questions:
The body needs every type of fat in order to function.
Only some fats are healthy.
All types of fat are bad for the body.
Lipids: More Than Just Bad Fats
Definition and Types:
Generically referred to as fats but include:
Fats
Oils
Phospholipids
Sterols (e.g., cholesterol)
Sources of Fats:
Plant Sources: Oils, nuts, legumes
Animal Sources: Fatty meats, full-fat dairy, seafood
Not Necessarily Fattening:
Lipids serve as energy-dense storage used by skeletal muscles, cardiac (heart) muscle, and the liver.
Commonly emphasized in popular diets such as Ketogenic Diets and Atkins diets.
Fat’s Bad Rap
Health Issues Related to Fat:
Poor health can result from:
Consumption of too much fat.
Consumption of too little fat.
Consumption of too much of certain types of fat.
Chemist’s View of Lipids
Main Types of Lipids:
Triglycerides (TGs):
Commonly referred to as fats.
Most abundant in foods and the human body.
Important distinction: Fat refers specifically to TGs, while Lipid includes TGs, phospholipids, and sterols.
Phospholipids
Sterols
Composition:
Includes carbon (C), hydrogen (H), and oxygen (O).
Lipids contain more carbon and hydrogen than oxygen.
Provides more energy per gram, specifically 9 kcals/gram.
Detailed View of Triglycerides
Triglycerides Makeup:
Composed of three fatty acids (FAs) typically present in combinations.
Contains a glycerol backbone.
Formed through condensation reactions (H from glycerol and OH from fatty acid create a bond, releasing one water molecule).
Structural Representation:
Glycerol and three fatty acids formula representation.
Chemist’s View of Fatty Acids
Fatty Acids Definition:
Organic acids with a methyl group (CH₃) at one end and an acid group (COOH) at the other end.
Identification:
Determined by the number of carbons (C) in the chain, which is usually an even number.
Abundant example: 18-carbon fatty acids.
Categories of Fatty Acids:
Long-chain (greater than 12 carbons)
Medium-chain (8 to 12 carbons)
Short-chain (less than 6 carbons)
Saturation Types:
Saturated: Fully saturated with hydrogens.
Unsaturated: Missing hydrogens, characterized by double-bonded carbon (C).
Types of Unsaturated Fatty Acids
Classification Based on Double Bonds:
Monounsaturated Fatty Acids (MUFA):
Contains one double-bonded C.
Example: Oleic acid (9 Cs away from CH₃).
Polyunsaturated Fatty Acids (PUFA):
Contains two or more double-bonded Cs.
Example: Linolenic acid is omega-3 (3 Cs away from CH₃); Linoleic acid is omega-6 (6 Cs away from CH₃).
Table 5-1: 18-Carbon Fatty Acids:
Name
Carbon Atoms
Double Bonds
Saturation
Common Food Sources
Stearic acid
18
0
Saturated
Most animal fats
Oleic acid
18
1
Monounsaturated
Olive and canola oils
Linoleic acid
18
2
Polyunsaturated
Sunflower, safflower, corn, soybean oils
Linolenic acid
18
3
Polyunsaturated
Soybean, canola oils, flaxseed, walnuts
Characteristics of Fats & Oils
Chemical Composition:
Determines number and positioning of double-bonded Cs, influencing the physical characteristics of fats and oils.
Degree of FA (Un)saturation impacts:
Firmness at room temperature:
Mono & Polyunsaturated fats (mostly from vegetables) are liquid.
Saturated fats (mostly from animals) are solid.
Saturated plant fats are solid but softer than animal fats.
Degree of Unsaturation affects:**
Firmness and stability:
Higher unsaturation leads to quicker oxidation and rancidity.
Saturated fats have longer shelf lives due to lack of double bonds.
Protection Against Oxidation
Manufacturer Options:
Use of expensive storage methods (air-tight, non-metallic, cold, dark environments).
Addition of antioxidants.
Hydrogenation process:
Adding hydrogen molecules to points of unsaturation, converting them to saturated fats.
Advantages: Longer shelf life due to less oxidation; alterations in texture.
Disadvantages: Partial hydrogenation can cause some double bonds to shift from cis configuration to trans configuration.
Trans-Fatty Acids
Understanding Hydrogenation:
Cis Configuration: Hydrogen (H) atoms on the same side of the carbon chain.
Trans Configuration: Hydrogen atoms on opposite sides of the carbon chain.
The body processes trans fats similarly to saturated fats, which can lead to increased blood cholesterol and heart disease risk.
Chemist’s View of Phospholipids
Phospholipids:
Make up approximately 5% of dietary lipids.
Composed of two fatty acids, a hydrophobic (fat-soluble) component, and a hydrophilic (water-soluble) phosphate group.
Functions:
Emulsifiers in the food industry.
Play a role in cell membrane structure, transporting vitamins and hormones in/out of cells.
Best-known phospholipid: Lecithin (found in eggs, liver, soybeans, wheat germ, peanuts).
Chemist’s View of Sterols
Sterols:
Have a multiple-ring structure.
Food Sources:
Cholesterol from animal sources (meat, eggs, seafood, poultry, dairy).
Plant sterols, which are structurally similar to cholesterol but impede cholesterol absorption.
Roles:
Various vital body compounds including bile acids, hormones (sex and adrenal), and vitamin D are derived from cholesterol.
Endogenous cholesterol is synthesized by the liver, while exogenous cholesterol comes from food sources.
Excess cholesterol can lead to plaque formation in artery walls, which is harmful.
Lipid Digestion and Absorption
Purpose: Break down ingested foods into smaller molecules for the body to use.
Digestion: Occurs primarily in the mouth, stomach, and small intestine, with lipids going from triglycerides to monoglycerides, free fatty acids, and glycerols.
Absorption: Lipids move into the bloodstream and undergo several transformations.
Lipid Digestion: Overview
Mouth:
Minimal digestion occurs (less than 5%) through lingual lipase.
Stomach:
Slightly more digestion occurs (5-25%) through lingual lipase and gastric lipase, yielding a mix of monoglycerides and free fatty acids.
Small Intestine:
Most digestion occurs (~75%).
Emulsification occurs through bile, which is stimulated by fatty acid presence and acts to break down large fat globules into smaller droplets.
Lipid Absorption in the Small Intestine
Bile salts encircle fatty acids and monoglycerides to form micelles.
Micelles pass through intestinal cell membranes via simple diffusion.
Inside the cells, fatty acids and monoglycerides are transformed back into triglycerides.
Triglycerides are coated by proteins to create chylomicrons, which are secreted via exocytosis into the lymphatic system, ultimately reaching general circulation.
Chylomicrons and Lipoproteins
Chylomicrons:
Largest type of lipoprotein, primarily serving the transport of triglycerides to peripheral tissues such as adipose tissue, muscle, and the liver.
Very Low Density Lipoproteins (VLDL):
Produced in the liver, contains less triglycerides than chylomicrons but still transports significant amounts. Transformed into low-density lipoproteins (LDL).
Low-Density Lipoproteins (LDL):
Made from VLDL and contains more cholesterol than triglycerides. Helps in delivering cholesterol to cells to support hormone production and cell membrane maintenance.
High-Density Lipoproteins (HDL):
Not derived from LDL. Synthesized by the liver, functions to transport cholesterol from peripheral cells back to the liver for recycling or disposal. Low levels of HDL can increase cardiovascular risk.
Conclusions and Reminders
Final Notes:
CFU #5 due on Mon, 10/6; follow-up on Lipids, Part 2 on 10/7.
CFU #6 opens on Thursday, 10/9, and is due on 10/13.
Midterm Exam opens on 10/14, with a review module available on Canvas. Optional Mid-term review lecture is scheduled on the same day, with assignments due by 11:59 PM on October 20.