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Chapter 5

Ch. 5 Lipids


Department
Food, Nutrition and Health
Course Code
FNH 250
Professor
Gail Hammond
Chapter
5

Page:
of 4
Lipids-organic, insoluble in H2O, 2-24 carbons (18C most common)
1. Triglycerides
-made up of 3FAs with a glycerol backbone, 95% of the fat we eat, how fat is
stored
-1 FA hydrolyzed -> diglyceride (DG) and if 2 FA hydrolyzed -> monoglyceride
(MG)
Chain Length
SCFA=less than 6C (dairy), MCFA=6-12C (coconut oil), LCFA=14-24C (meat)
Saturation
Saturated FA (SFA) -> cream, coconut/tropical oil, chocolate, milk fats
MUFA-omega-9 family (double bond 9 Cs from methyl end) -> olive, canola,
peanut oil, avocado
PUFA-omega-6 family -> corn, soybean, sesame oil and omega-3 -> fish, canola,
hemp, flaxseed oil, nut
-use ratio of # Cs to # double bonds to name them (eg. 18:1 is monounsaturated
18-C FA)
-if unsaturated, either cis (more kinked) or trans (more straight and like saturated
fats)
-double bonds affected by O2, UV light, chemicals -> rancidity
Hydrogenation
-prevents rancidity by saturating double bonds, changing cis to trans
-saturated fats increase blood cholesterol + risk of heart disease (and trans too,
since similar)
Essential FAs
-dietary fat provides the 2 EFA needed to make compounds…
1. Linoleic Acid-omega-6, C18:2; in veggie + seed oils, nuts
-helps regulate blood clotting + blood pressure, needed for cell membrane
integrity
-precursor to arachidonic acid (AA), C20:4
2. Linolenic acid-omega-3, C18:3, in fish, flaxseed, canola oil, soybeans, wheat
germ
-precursor to EPA + DHA -> used in retina + cerebral cortex, found in human
milk, shellfish
-AI is ratio of 10:1 for omega 6:3
Function
Triglycerides…
1. Fuel Source
-major E source for muscles at rest + during light activity (to conserve carbs)
-enzyme lipase breaks down TG from adipose (low insulin levels-prevents fat
breakdown) -> cross adipose cell membrane -> travel thru blood bound to
protein albumin to muscle -> when cells need E, break down further (B-oxidation)
-> use O2 to make ATP (if more fit, burn more fat b/c more O2)
-during activity, draw E from blood lipoproteins, adipose, muscle, dietary fat
-need CHO to oxidize FA: 2C fat fragments combine with oxaloacetate (made from
CHO) in Kreb’s -> if not enough, left with excess 2-C fats -> body deals with by
making ketones
2. Fuel Storage
-non bulky storage since TG packed tightly w/ little water
3. Insulation/Protection
4. Structural-myelin sheath, hormones, keep cells fluid + flexible
5. Transport FS Vitamins
6. Satiety-stimulates hormone that delays gastric emptying
7. Flavour + Texture-many flavours dissolve in fat to enhance taste
Fatty Acids…
1. EFA=form eicosanoids-20C FAs, include prostaglandins, thromboxanes,
leukotrienes
-those made by omega-3s decrease blood clotting, BP, inflammation, and dilate
blood vessels
-those made by omega-6s increase blood clotting, BP, inflammation, constrict
blood vessels
2. Immune system-enhance WBC response, help vision (more unsaturated = better
response)
3. Integrity + fluidity of cell membranes-esp. phospholipids
2. Phospholipids
Functions-cell membrane, neurotransmitters, emulsifier (in bile), micelle formation
Sources of lecithin-liver makes enough, but can get from egg yolk, liver, soybeans,
chocolate
3. Sterols
-multiple ring structure
-dietary cholesterol is not blood cholesterol (eg. LDL + HDL)
-dietary = used to make chylomicron -> remnant in liver -> repacked into VLDL,
LDL, HDL = blood c.
-different transport vehicles (lipoproteins) transport cholesterol in blood
Functions of Cholesterol
1. Precursor-for hormones (sex), bile, vitamin D
2. Cell Membranes-structural component, esp. in brain, spinal cord, neural cells
3. Myelin Sheath-allows proper conduction of nerve impulses
4. Can be good/bad-only 1 type -> depends on how carried in blood + where
located
Sources-liver makes enough, but can get from egg yolk, organ meats, fish (animals
only)
Breaking Down Lipids
-since not H20-soluble, can’t enter blood from digestive tract
SI-PL get 1 fat hydrolyzed -> remaining PL + FA get absorbed
-sterols are absorbed intact (not digested)
Lipid Transport
Lipoprotein-includes chylomicron, VLDL, LDL, HDL (all have hydrophilic shell +
hydrophobic interior)
-each has diff amounts of lipid components + unique protein profile
a) Dietary Lipids
Chylomicron=transport vehicle for dietary lipids, mostly TGs (reflects what we eat)
-after travelling through blood + cells, left w/ remnant of protein, cholesterol, PL
-liver removes remnant from blood -> makes bile from cholesterol, breaks down
proteins
b) Non-Dietary Lipids
1. VLDL-when liver packs fats (mostly TG, some cholesterol, PL) + PRO into a
lipoprotein
-released into bloodstream to deliver lipids to body cells (fats = less dense,
PRO=more dense)
-cells remove TG via LPL + VLDL picks up cholesterol from (eg. HDL) -> smaller
size, more dense
2. LDL-mainly cholesterol, some PL, PRO, little TG
-primary cholesterol delivery system in blood for all cells
- delivers cholesterol from liver to cells -> make steroid hormones, build new cell
membranes, use
-LDL receptors on liver cells bind to protein in LDL + remove LDL from circulation
-> lower levels
-LDL endocytosed into liver -> hydrolyzed to release cholesterol, FA, aa
-the more SFA in diet, the less LDL receptor activity
Heart Disease…
-injured blood vessel -> WBC sent, vessel wall more permeable -> small LDL
adhere to wall + get oxidized -> engulfed by WBC -> cholesterol builds up in
cell, forming “foam cell” -> foam cell bursts, forms fatty streak along vessel wall
-> platelets attracted, form plaque -> artery more rigid + narrow -> increased
blood pressure -> block off blood supply -> heart attack/stroke
-antioxidants can reduce LDL oxidation (more LDL circulating = more likely to be
oxidized)
3. HDL-greatest proportion of protein, picks up cholesterol from adipose + dying
cells
-takes cholesterol to the liver for recycling (eg. into bile) + removal via bile
excretion
-made by intestine + liver, can transfer cholesterol to VLDL via cholesterol ester
transfer PRO
Desired LDL: HDL ratio is < 4.5-5:1
How much to Eat
-AMDR for fat is 20-35% total E
-AI for linoleic acid is 14-17 g/day for men, 11-12g/day for women (5-10% total E
intake)
-AI for alpha-linolenic acid is 1.6g/day for men, 1.1g/day for women (0.6-1.2% total
E intake)
-best ratio of SFA:MUFA:PUFA is 1:1.5:1 (MUFA only has 1 double bond -> less likely
to be oxidized and lose its purpose)
Visible Fats-can see in foods, or added to foods (eg. butter, cream, chicken skin,
mayo, oils)
Invisible Fats-hidden in foods like baked goods, marbling in meat, fried food,
cheese, milk products
-“low-fat” foods may still give you similar E intake since reduced fat often replaced
with added carbs -> you might eat more b/c you think it’s low-fat and end up
getting more Calories overall
Beneficial Fats
-omega-3 FAs can: lower risk of heart attack, slow rate of cognitive decline
-fish oil supplements costly, may have heavy metals, increase bleeding time, reduce
immune function
Fat Replacers