chapter 5 lipids (1)

8/2/2019 Chapter 5 Lipids (1)

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Chapter 5 LIPIDS

The good, the bad and the very bad



What are Lipids?

Organic molecules that contain C, H, and O(lower concentration than in carbs); mostlyinsoluble in water.

Fats –

Oils –

3 classes:

Triglycerides Phospholipids

Sterols – cholesterol, etc.



What’s Good About Lipids? Functions:

An energy store – 9 calories/gram and it islightweight compared to glycogen.

Fat depots are shock absorbers for our vital

organs. Fat provides insulation.

Ingested fats contain fat-soluble vitamins

Lipids form cell membranes Lipids provide raw materials (cholesterol) for

vitamin D and hormones.



Fig. 5-1, p. 141

muscletissue

fattissue

bloodcapillaries

Fatcell

cellmembranenucleus

lipids enterfrom blood

lipids exit

to blood



Lipids in Foods

Fat adds flavor and pleasing odors

Fat tenderizes

Fat makes us feel “full” = satiety

Fat is a nutrient and there are “essential fatty

acids”.

Fat transports fat soluble compounds likevitamins and some phytochemicals.



Triglycerides

Composed of glycerol and 3 fatty acid chains,fig 5.3, 5.4

Fatty acid (FA) chains can be short or long

FA chains can be saturated or unsaturated(missing hydrogens). Missing hydrogens causesdouble bonds to form between carbon atoms anda kink in the chain.

1 double bond = monounsaturated

2 or more double bonds = polyunsaturated (PUFAs)


http://slidepdf.com/reader/full/chapter-5-lipids-1 7/48Fig. 5-3, p. 143

glycerol

3 fatty acids

of differinglengths

A triglycerideformed from 1

glycol + 3 fattyacids


http://slidepdf.com/reader/full/chapter-5-lipids-1 8/48Fig. 5-4, p. 144

Saturated Monounsaturated Polyunsaturated

Point of

unsaturation

Points ofunsaturation



Triglycerides

Triglycerides with short or unsaturated FA areliquid (oils), triglycerides with long or saturated FAare solids (fats).



Triglycerides

Choosing the right fats

Many plant derived fats are unsaturated oils.Careful!!! – study figure 5.5.

Coldwater fish derived fats are usuallyunsaturated oils.

Food fats are a mixture of saturated andunsaturated triglycerides.



Fig. 5-5, p. 145



Phospholipids

Functions



Sterols

Composition

Large molecules made of multiple ring structuresinstead of glycerol. Chains of C, H, and O are

attached to rings. Functions:

Cholesterol –

Vitamin D –

Steroid hormones –



Lipids in the Body

Digestion

Mouth – some break down of milk fat in the mouthof infants; no digestion in adults.

Stomach – fats float on watery chyme; nodigestion



Lipids in the Body

Digestion cont’d

Small intestine

Fats are mixed with bile from the gall bladder and are

emulsified, fig 5.6. Enzymes from the pancreas break down fats into

glycerol, free fatty acids and monoglycerides all of whichcling to bile.



Fig. 5-6, p. 146

Fat Fat

Waterydigestive

juices

Enzymes

Bile

Emulsifiedfat

Emulsifiedfat

In the stomach, the fat and

watery digestive juicestend to separate. Enzymesare in the water and can’t

get at the fat.

When fat enters the small

intestine, the gallbladdersecretes bile. Bile has anaffinity for both fat andwater, so it can bring thefat into the water.

After emulsification,

more fat is exposed tothe enzymes, and fatdigestion proceedsefficiently.

Enzyme



Lipids in the Body

Absorption

Small Intestine

Break down products are absorbed into cells of intestine

and bile is removed, fig 5.7. Small products move directly into blood and travel to the

liver.

Large products are reassembled into triglycerides, andcombined with proteins to form chylomicrons ( a type oflipoprotein). These are transported in lymph and enterthe bloodstream near the heart.



Fig. 5-7c, p. 148

Small lipids

Large lipids

Capillarynetwork

Lymph

Villi

Bloodstream

Chylomicrons

Blood vessels

Lymph to blood

3 The parts are absorbed byintestinal villi.Small lipid particles such as

glycerol andshort-chain fatty acids aresmall enough toenter directly into thebloodstream.

3



Lipids in the Body

Absorption cont’d

Fat absorption is 98% efficient – high fat mealsslow stomach emptying and digestion.

Cells remove what they need and the rest ispicked up by the liver, broken down and recycled.



Lipids in the Body

Transport of fats

Pure lipids would float in the blood.

Liver produces proteins and combines them with

fats = lipoproteins, fig 5.9 VLDL –

LDL –

HDL –

100



Fig. 5-9a, p. 151

Protein

Cholesterol

Phospholipid

Triglyceride

Higher densityLower density

LDL(more lipid,

less protein)

HDL(Less lipid,

more protein)

100

80

60

40

20

0



Lipids in the Body

Lipid profile tests usually include:

Total Cholesterol

Triglycerides (Trigl)

HDL &/or LDL

You can calculate

LDL = Cholesterol – HDL – Trigl/5

VLDL = Trigl/5



Lipids in the Body

Using stored fat

The body uses blood glucose 1st, then breaksdown glycogen (stored glucose).

Most organs use fats when blood glucose levelsare low and glycogen storage has been depleted.

Cells break down fats, **combine them withfragments from glucose and harvest energy using

chemical reactions (Krebs Cycle).



Lipids in the Body

Using Stored Fat

Without glucose fragments, fats are broken downinto ketones causing ketosis.

Excess glucose can be converted to fat!



Lipids and your Health

High fat diets are associated withcardiovascular disease (CVD) and somecancers. Figure 5.11 shows common

sources of fat in our diet. High fat diets cause obesity that is associated

with diabetes.



Fig. 5-11, p. 154




Risk Factors for Developing CVD

Genetics, diabetes

Age – men over 45, women over 55

Elevated LDL

Low HDL

Hypertension

???Gender




Lifestyle Risk Factors

Cigarette smoking

Obesity

Decreased physical activity

Diet high in fat, low in fruits, vegetables and wholegrains (FIBER). Fiber decreases the absorptionof fats in the small intestine.



Significance of LDL and HDL

Cholesterol intake can raise blood cholesterolbut is not the major factor.

Fat in the diet causes an increase in LDL that

carries cholesterol TOWARD the tissues (in theblood). High levels of LDL (& VLDL becausethey become LDLs after delivering their fats)clog arteries.

HDL’s carry cholesterol AWAY FROM thetissues – a good thing.



Significance of LDL and HDL

How do we decrease LDL?

How can we increase HDL?

LDL can be oxidized and become a further

threat. Solution: add antioxidants to yourdiet – vitamins C and E, ?phytochemicals.



Essential Polyunsaturated Fatty Acids

Most fatty acids can be made by the bodyusing carbohydrates, proteins or fats.

Exceptions: linoleic (omega-6) and linolenic

(omega-3) acids. These are essential fattyacids, i.e. must be included in your diet!

DRIs:

Linoleic acid: 12-17 g/day, young people Linolenic: 1.1-1.6 g/day




Functions of Omega 3 and 6 fatty acids,Table 5.3.

Provide raw material for eicosanoids, substances

that regulate BP, blood clotting, immuneresponses, etc.

**The primary fats in your brain/nerves.

Essential for growth and good vision in young

people.




Deficiencies are rare but are associated withskin problems, reproduction failure, kidneyand liver disorders, etc.

Sources: oils from grains, nuts, seeds, leafyvegetables and cold water fish (salmon, tuna,mackerel, sardines, etc.). **

Is fish safe to eat? What about fish oilsupplements? **Read pp. 156-158.



Processing of Fats

Unsaturated fats are subject to oxidation andbecome rancid.

Cure: Hydrogenation = adding hydrogens to

the FAs. Hydrogenation is also used to makeoils more solid (margarine) and increase“smoking point”.

Problems: Produces trans fats that increaseLDL and decrease HDL, fig 5.12.



Fig. 5-12, p. 159



Processing of Fats

Sources of Trans Fats

Fried FAST FOODS – hydrogenated vegetableoils.

Other culprits, fig 5.13.

Commercial cakes,



Fig. 5-13, p. 160

Candies1%

Breakfastcereals

1%

Saladdressings

3%

Householdshortening

4%

Potato chips, cornchips, popcorn

5% Friedpotatoesc

8%

Milk and otherdairy products; meatb

21%

Margarined 17%

,cookies

crackers, doughnuts,pies, bread,

other bakery items

40%



Fat in the Diet – From the Pyramid

#1 – Red meats and nuts*.

#2 – Milk, milk products, breads

#3 – Olives and avocados

What about replacements?

Olestra – side effects?

Read – “Consumer Corner”, pp 162-164.



Fat in the Diet

Meat has visible and hidden fat (marbeling),including turkey, fig 5.16. When you fry it, upto 50% of the calories are from fat.

Which ground meat is best?



Fig. 5-16, p. 165



Fat in the Diet

Milk, yogurt and cheese – varying content offat. These are also good sources of proteinand calcium – things you need. Butter and

cream are mostly fat, fig 5.17. Choose lowfat or no fat varieties.



Fig. 5-17, p. 166



Fat in the Diet

Bread, cereal, rice and pasta – ingredientsare naturally low in fat but processing/cookingcan add a significant amounts of fat, fig 5.18.

Read the labels!



Fig. 5-18, p. 167



How to Cut Down on Fat in your Diet

What are some ways we can cut down on ourfat intake?



CS 5-1, p. 176

1% increase indietary saturated

fatty acidsa

1% decrease indietary saturated

fatty acidsa

2% increase in bloodLDL cholesterol

2% decrease in bloodLDL cholesterol

2% increase inheart disease riskb

2% decrease inheart disease riskb



How to Cut Down on Fat in your Diet

Fast Food choices – figure 5.19.

Read the “Controversy” – Which one of youwould like the Mediterranean Diet?

chapter 5 lipids (1)

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