Chapter 6:The Lipids

…a PHAT chapter…

Self-check

• What hormone helps to prevent hyperglycemia?A. InsulinB. GlucagonC. GluconeogenesisD. Glycogenolysis

Self check

• What term best describes glycogen getting broken down and used for energy?

A. GluconeogenesisB. HypoglycemiaC. GlycogenolysisD. Type 2 diabetes

“Over the last few decades, people have heard nothing but conflicting messages about fat…•Get rid of it entirely• Eat a little bit• Eat only certain types

….I think people have gotten a bit fed up with the changes, and so they’re throwing them all out.”

--Susan Allport, author of The Queen of Fats

Basic Principles of Chemistry (important for understanding lipids)• Atoms are usually connected (or bonded) to other atoms • Carbon atoms are unstable unless they contain four bonds• Oxygen atoms are unstable unless they contain two bonds• Hydrogen atoms are unstable unless they contain one bond

Double bond between carbon atoms

Single bond between carbon atoms

Basic Principles of Chemistry (important for understanding lipids)• Terminology

Carboxylic AcidMethaneMethyl group

Basic Principles of Chemistry (important for understanding lipids)• Terminology

Glycerol Glycerol (written out in chemistry shorthand)

What is a Lipid?• Macronutrient (9 kcal/gram)• Made up of carbon, hydrogen, oxygen• Insoluble in water (ie can’t dissolve in

water)• Soluble in organic solvents (can dissolve

in substances containing carbon)• Food sources:• Animals (example: animal fat, butter, milk

fat)• Plants (example: vegetable oils, nuts,

avocados)

DRAW IT!

The Four Major Categories of Dietary Lipids

1. Fatty Acids• Chains of carbon atoms with hydrogen atoms attached• Contain a methyl end (also called “omega” end) and a carboxylic acid end• Carbon chains vary in length. Chain length confers health properties!• Short Chain Fatty Acid (SCFA): Less than 6 carbons• Medium Chain Fatty Acid (MCFA): 6-12 carbons• Long Chain Fatty Acid (LCFA): More than 12 carbons

Fatty Acids: Two Types• Saturated fatty acid• Less healthy; intake should be limited• Usually solid at room temperature• Major food sources:

• Animals – meat and dairy• Plants – coconut oil, palm kernel oil, palm oil

• Unsaturated fatty acid• More healthy; saturated fats should be replaced in the diet with unsaturated fats• Characteristics: Usually liquid at room temperature• Major food sources:

• Fish – fatty fish • Plants – seeds, nuts, grains, vegetable oils

Saturated Fatty Acids• Fatty acids that contains all single bonds (NO double bonds) and carry

the maximum number of hydrogens• SHAPE: Flat

Unsaturated Fatty Acids• Unsaturated Fatty Acids – fatty acids that contain AT LEAST ONE double bond and have less

hydrogen atoms• Monounsaturated Fatty Acids (MUFA) – fatty acids with ONLY ONE double bond in the carbon chain• Polyunsaturated Fatty Acids (PUFA) – fatty acids with TWO OR MORE double bonds in the carbon chain

SHAPE: BENT (NOTE: fatty acid side chains usually bend at the double bond)

Fatty Acids: A comparison of saturated and unsaturated chains

What is the name of this end?

Carboxylic acid group

What is the name of this end?

Methyl group

Fatty Acids: “Cis” vs “Trans”• Double bonds can be Cis or Trans

Trans fatty acids

• Found naturally in low levels in the food supply (milk, dairy)• Caused by a process called hydrogenation • Add hydrogen to liquid oils• Liquid oil becomes solid (example: add hydrogen to vegetable oil makes

margarine)• Confers desirable food properties: longer shelf life, better texture in baking• Forms many trans fatty acids

• Fatty acids contain double bonds, which usually cause bent fatty acid side chains• But….• Now there are many fatty acids with double bonds that are flat….• What other fatty acids are flat? What can we deduct from the SHAPE of trans fatty

acids?

Trans Fatty Acids

• “As little as 1% of total calories (from trans fats) can increase the risk of heart disease and stroke…” –Text, page 132• Major food sources of trans fats:• Processed & commercial baked goods (cakes, cookies, pies, biscuits, doughnuts)• Foods containing shortening or margarine• Packaged snacks (popcorn, crackers)• Frozen pizza• Fried potatoes

• Finding & avoiding trans fats: look for “partially hydrogenated” on the food label

2. Triglycerides• Glycerol – a 3 carbon compound that makes up the backbone of the

triglyceride moleculebonded to

• THREE Fatty Acid side chains “Tail” of

triglyceride

Triglycerides

Functions of triglycerides• Primary source of dietary fat (95%)• Supply energy…. How much energy do they supply per gram?• Assist with absorption and transport of fat-soluble vitamins • Primary storage form of fat; found in adipose tissue

Fatty Acid Composition of Common Sources

3. Sterols• Sterols – complex lipids with interconnected carbon rings and a side

chain of carbons and hydrogens

The Best Known Sterol: Cholesterol

What do all these foods have in common?

Cholesterol• Necessary to sustain life…• Functions:• Stabilizes cell membranes• Precursor (building block) for the synthesis of bile, vitamin D, steroid hormones• Does not provide energy (calories)

• Only comes from animal sources!• Synthesized in the body (primarily in the liver)

4. Phospholipids• Phospholipid – • Glycerol backbone• TWO Fatty acid side

chains (water hating)• ONE phosphate

group side chain (water loving)

4. Phospholipids

Lipid Digestion and Absorption• Emulsification – process that allows lipids (fats) to mix with water• Lipase – enzyme that removes fatty acids from the glycerol backbone

of triglycerides• Lipoproteins – particles formed by the assembly of proteins and

phospholipids; transport lipids in the lymph and blood

1. Bile acids attach to lipid globules2. Lipids are dispersed into smaller

droplets3. Lipase digests triglyceride to

monoglycerides and free fatty acids4. Divested lipids are packaged into

micelles 5. Lipids leave micelle and are

absorbed into mucosal cells6. Lipids are repackaged into

chylomicrons and moved into lymph vessels

Lipid Digestion & Absorption

Lipoproteins• Low Density Lipoprotein (LDL) – a lipoprotein responsible for transporting

cholesterol from the liver, through the blood, and into tissues• High Density Lipoprotein (HDL) – a lipoprotein responsible for transporting

cholesterol from the bloodstream and tissues back to the liver