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Chapter 5: Lipids & SterolsTURN OFF PHONES Objectives: • Student Understanding of

– Basic Chemical Structure and food sources • Triglycerides / Fatty Acids

– Monounsaturated, Polyunsaturated & Saturated Fats– -3 and -6 Fatty Acid

• Phospholipids• Sterols

– Major roles of fats/lipids in body– Basic Digestion, Absorption, and Transport of Lipids– Health Effects of Lipids– Health/Dietary Recommendations related to fat and cholesterol

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What are lipids?• Lipids are a group of organic, energy yielding macronutrients, most of which do not dissolve in water and are essential.• Lipids in the diet and in the human body include (3):1)Triglycerides/Fatty Acids2)Phospholipids3)Sterols

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Functions of Lipids in the Body• Energy:

– Major source of energy– Stored in the adipose tissues

• Protection:– Temperature, Shock

• Structural:– Components of cell membranes

• Regulation:– regulates blood clotting and blood pressure

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The Three Types of Lipids• Fatty Acids / Triglyceride• Phospholipids• Sterols

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Fatty Acids• Fatty acids:are organic molecules made up of chains of carbon atoms with attached hydrogen atoms and an acid group at one end.

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Classification of Fatty Acids(Saturation)• Degree of Saturation:- A Saturated fatty acid is fully occupied by hydrogen atoms

- A Monounsaturated fatty acid has one double bond between carbons where a pair of hydrogens are “missing”- A Polyunsaturated fatty acid has two or more double bonds between carbons

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Structure and FunctionWhat effect does chain length and saturation have?Shape: solid vs liquidLength: Shorter chains are more easily absorbedHealth: heart healthSaturation: helps stabilize shelf lifeStructure Changes function

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Why do we hydrogenate oils?• Hydrogenation makes oils less prone to spoilage and makes them remain solid at higher temperatures. (Used in making margarine from vegetable oils)

• Partial Hydrogenation leads to more trans fatty acids.• Trans fatty acids have been linked to the similar problems as saturated fats within a lesser amount in the diet

• Cis fatty acid Trans fatty acid Saturated fatty acid

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Essential Fatty Acids• In Omega-6 fatty acids• In Omega-3 fatty acids• These two types of fatty acids are specific precursors to important regulatory molecules and are therefore considered “Essential” in the diet.

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Triglycerides• The foods we eat contain TRIGLYCERIDES.• A triglyceride (or triacylglycerol) consists of three fatty acids attached to a molecule of glycerol.• The three fatty acids in a triglyceride may be all the same or different.

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What is a Phospholipid?• A phospholipid is like a triglyceride in which one fatty acid has been replaced by a phosphate group.• The phosphate group is soluble in water, while the fatty acid “tails” are not.• Phospholipids are thus hydrophilic at one end and hydrophobic at the other end

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Primary Functions of Phospholipids

Bi-layerCell Membrane

Single LayerLipid Transport

(a.k.a. Lipoproteins)

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What are sterols?• Sterols are a family of molecules consisting of interconnecting carbon rings.• The most common form of sterol in the human body is cholesterol.

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Facts about Cholesterol• The body uses cholesterol for making certain hormones, bile, vitamin D and cell membranes.• Only animals produce cholesterol• The body routinely manufactures cholesterol for its own use.• In foods

– Plants and animals have sterols– Only animal tissues contain CHOLESTEROL

• Highest in organ meats• Egg yolk

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Digestion of Fat/LipidsMouth* Some fats melt

Stomach*Fat floats, but some mixes with acid and water

Small IntestineGallbladder secretes bile and fats are emulsified

*(minimal digestion does occur in the mouth and stomach however we will consider this

insignificant)

Lipids in the Digestive Tract

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• Bile emulsifies Lipids: breaks down large droplet of fat into much smaller droplets.• Fat-digesting enzymes are also released.a.k.a. Pancreatic Lipase • Once broken down they form micelles (a cluster of fatty acids). • These fatty acids are absorbed across the lining of the small intestine.

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Digestion of Fat Begins with Emulsification

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Micelles are small droplets of primarily fatty acids (and other fat soluble substances) that are absorbed across the lining of the small intestine. From here they are packaged into Lipoproteins for transport.

Lipids in the Digestive Tract

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Digestion of Fat/LipidsSmall IntestinePancreatic lipases turn:

Fats into monoglycerides and fatty acids

Absorption takes place.

Once absorbed fat will be transported primarily by Lipoproteins.

• Lipoproteins (4 Types): are spherical bodies with a phospholipid/protein shell that contain different types of lipids.– Chylomicrons are large lipoproteins that carry lipids from the small intestine, first via the lymph system, and eventually into the blood stream.

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Lipoproteins:The Transporters of Fat

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Lipoprotein Size and Content

Triglyceride

ProteinCholesterol

Phospholipids

• Lipopropteins from the Liver– Very low-density lipoproteins

(VLDLs) are formed in the liver from partially spent chylomicrons and function to deliver lipids to body cells.

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More Transporters: Lipoproteins Continued

Triglyceride

Protein

Cholesterol

Phospholipids

• Lipopropteins from the Liver– Very low-density lipoproteins

(VLDLs) are formed in the liver from partially spent chylomicrons and function to deliver lipids to body cells.

– Low-density lipoproteins (LDLs)A.K.A the Bad Cholesterol are formed in the liver from partially spent VLDLs and again circulate through the body delivering lipids.

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More Transporters: Lipoproteins Continued

Triglyceride

Protein

Cholesterol

Phospholipids

• Lipopropteins from the Liver– Very low-density lipoproteins (VLDLs) are

formed in the liver from partially spent chylomicrons and function to deliver lipids to body cells.

– Low-density lipoproteins (LDLs)A.K.A the Bad Cholesterol are formed in the liver from partially spent VLDLs and again circulate through the body delivering lipids.

– High-density lipoproteins (HDLs)A.K.A. the Good Cholesterol circulate through the body, removing excess cholesterol from other lipoproteins and body cells.

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More Transporters: Lipoproteins Continued

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Digestion of Fat/LipidsSmall IntestinePancreatic lipases turn:

Fats into monoglycerides and fatty acids

Absorption, Transport takes place

Colon Some fat and cholesterol bound to fiber exit in feces

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Fats and Health• Saturated fats* Increases Total Cholesterol (TC) and LDL• Trans fats Increase TC and LDL while Decreasing HDL• Dietary Cholesterol Increases TC and LDL• (*the greater concern is Saturated Fats) • Polyunsaturated Fats Decreases TC (HDL and LDL)• Monounsaturated Fats Decreases TC & LDL with less effect on HDL• Exercise may increase HDL

Negative Effects on Blood CholesterolPositive Effect on Blood Cholesterol