Chapter 5 lipids

The Chemist’s View of Fatty Acids and Triglycerides • Triglycerides are lipids with three fatty acids attached to a glycerol... Saturated Fatty Acids• All the carbon bonding sites are f

• Lipids – Chapter 5

Functions of Dietary Lipids

• Concentrated source of energy

– 9 kcal/gram

• Satiety value

• Source of essential fatty acids

• Carrier of fat soluble vitamins

• Flavor

Role of Lipids on the Body

• Reserve of energy (Storage)

• Insulation against the cold

• Protection of vital organs

• Body regulator

Lipid Classes

• Triglycerides

• Phospholipids

• Sterols

• Glycerides

• Composed of glycerol (alcohol) & fatty

acids (organic acid)

• Found in food & body fat or adipose tissue

• Efficient way to store energy

Food sources of fat

Adipose cell

In relation to Muscle cell & capillaries

The Chemist’s View of Fatty Acids

and Triglycerides

• Triglycerides are lipids with three

fatty acids attached to a glycerol

Fatty Acids

• Number of carbons range from 4 to 24

• Always even numbers

• Organic acid

Acetic acid: a fatty acid Two carbon organic acid

T r i g l y c e r i d e

Degree of Saturation

Saturated Fat

• Often called the heart disease factor

• Composed of Triglycerides in which most

of the fatty acids are saturated

Saturated Fatty Acids

• All the carbon bonding sites are filled with

H atoms

• No double bonds between carbon atoms

Saturated fatty acid – stearic acid

18 Carbon Saturated Fatty Acid

Unsaturated Fat

• Composed of Triglycerides in which most

of the fatty acids are unsaturated

Unsaturated Fatty Acids

• One or more points in the carbon chain

with a double bond between carbon atoms:

– Monounsaturated (MUFA)

– Polyunsaturated (PUFA)

Monounsaturated Fatty Acids

• One double bond in the carbon chain

• Oleic acid is an 18-carbon

monounsaturated fatty acid

Monounsaturated fatty acid – Oleic Acid

18 Carbons

Polyunsaturated Fatty Acids

• PUFA

• More than one double bond in the carbon

chain

• Linoleic acid is an 18-carbon fatty acid

with 2 double bonds Omega 6

• Linolenic acid is an 18-carbon fatty acid with 3 double bonds Omega 3

Polyunsaturated Fatty Acids

Stearic acid, an 18-carbon saturated fatty acid

Oleic acid, an 18-carbon monounsaturated fatty acid

Linoleic acid, an 18-carbon polyunsaturated fatty acid

Triglyceride Synthesis

Fat in Foods

• The physical characteristics of fat in food

depends on the type of fatty acids present

• Fat in foods is a mixture of saturated,

monounsaturated and PUFA

Fat in Foods

– Solid at room temperature

– Usually animal sources

• Coconut oil, palm oil, palm kernel oil, cocoa butter are from plants but saturated fats

– they are firmer but softer than

animal fats (8-14 C)

Saturated fats

Fat in Foods

• Polyunsaturated fats

– Usually plant source

– Liquid at room temperature

• Safflower, sunflower, corn, soybean, &

cottonseed oil

Unsaturated fats

Fatty Acid Composition in

Foods

• Saturated fat is more resistant to oxidation.

• Monounsaturated fat is slightly less

susceptible to spoilage.

• Polyunsaturated fat spoils most readily.

• Protection from rancidity

– Sealed in air-tight containers away

from light

– Add antioxidants

– Hydrogenation

• Adding hydrogen back to an unsaturated

fatty acid to make it a more saturated fatty acid and

• Double bonds are easily attacked by oxygen

• Example

– Crisco shortening from soybean oil

• Man-made

Cis & Trans Configuration

• In nature: most double bonds are Cis

– Hydrogens are in the same side

• After hydrogenation, the unsaturated

double bonds change from Cis to Trans

– Hydrogens are in the opposite side

• Trans-FA: act as a saturated fat

• Linoleic acid: natural trans-fat

Cis & Trans FA Compared

Essential Nutrients

• Necessary for life or growth

• Body cannot make them or

• Body cannot make fast enough for growth

or life

Essential Fatty Acids

• Linoleic Acid C18:2 Omega 6

• Linolenic Acid C18:3 Omega 3

Essential Fatty Acids

• Need 3% of total kcal from essential fatty acids

• Deficiency of essential fatty acids

Omega-3 & Omega-6

Fish Oils

• Omega-3 fatty acids are high in fish oils

Vegetable Oils

• Omega-6 fatty acids are high in vegetable

oils

• Triglycerides are the most common lipid

on the diet !

• Phospholipids and sterols make up only

5% of the lipids from the diet.

Phospholipids

More complex

structure than TG

Lecithin

Phospholipids in Foods

• Role in food

– Emulsifier - keeps fat miscible with

water

– Are mostly found in egg yolk, liver,

soybeans, wheat germ & peanuts

• Role in the body

– Part of cell membrane

– Liver makes lecithin

– Lecithin is NOT an essential

nutrient

Fig 5-10, p 146

• Dissolve in water and fat

• Help movement of lipids inside the cells

and outside the cells

• Help vitamin and hormones to pass the

cell membrane

• Help to keep fats suspended in the blood

and body fluids

Sterols

Fig 5-11, p 147

Cholesterol

Vitamin D 3

Sterols in foods

• Plants and animals have sterols

• Cholesterol comes from ANIMALS

• Plant sterols interfere with Cholesterol

absorption

• Cholesterol -> ONLY ANIMAL foods

• Meats, eggs, milk, poultry, fish.

• Endogenous sources

– The body can make it!!

– Liver can make 800 – 1500 mg/day – More than what you consume from

the diet.

• Starting material for many components:

– hormones and vitamins,

– structural component of cell membranes

Sterols & Hormones

• What is a hormone?

– Chemical messengers

Sterols & Hormones

• Examples of hormones that are sterols

– Progesterone

– Testosterone

– Estradiol

Cholic Acid is a Sterol

• Cholic acid is part of bile salts which are

needed to digest lipids

Fig 5-13, p 150

Sterols & Vitamin D

• Vitamin D is made from cholesterol

precursor in the skin

Cholesterol

Vitamin D 3

Cholesterol In selected foods

Fig 5-22, p 158

Cholesterol in foods

Cholesterol in Blood

• Chylomicron

• Very low density lipoprotein (VLDL)

• Low density lipoprotein (LDL)

• High density lipoprotein (HDL)

Health Effects of Lipids

– Cholesterol: arterial plaque

– Increase LDL cholesterol → ↑ risk CD

– Most saturated fats come from….

– decrease LDL

Health Effects of Lipids

Health Effects of Lipids

• Omega-3:

– High consumption decrease risk of

heart attack and stroke.

– Prevent blood clotting

– Prevents arrhythmia

– Lower blood pressure

– Fatty fish

Health Effects of Lipids

• Balance Omega-3 & Omega-6:

– Eat more Fish

– American Heart Association

recommends 2 servings/week

– Salmon, mackerel…

– Eat fish grilled, broiled, baked – Do Not Fry!!!

Health Effects of Lipids

• Balance Omega-3 & Omega-6:

– Functional foods to add Omega-3:

– Capsules of Fish Oil

– High intakes of Omega-3 may increase bleeding, alter immunity, raise LDL

– Recommended Omega-6 to Omega-3 ratio: 6:1

• Consume more lean meats

• Trim fat

• Consume low fat or fat free milk

• Consume more fruits and vegetables

• Consume more whole grains and legumes

• Read the Labels!!!

Invisible Fat

• Less apparent

• Cheese

• Fried foods: like chips…

• Many baked goods

• Chocolate bars

• Cream soups

Fat Replacers

• Derived from Carbohydrates, protein or fat

• The body may digest or absorb them

Questions?

Review of Lipids

• How do we classify lipids?

• Where can we find TG?

• Where can we find Phospholipids?

• Where can we find Sterols?

• Why do we use hydrogenation?

• How can we find Cholesterol in Blood?

Fatty Acids