Transcript lect 4 strachan coursenotes

Lipids
Basic Human Nutrition
Lecture 4
Elisabeth Strachan
Lipids
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Family of compounds that includes
triglycerides, phospholipids, and sterols.
Fats are solids are room temperature;
oils are liquids at room temperature.
Excess energy is stored in the body as
fat (triglycerides).
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Lipids continued
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Serve as energy reserves.
Cushion the vital organs.
Protect the body against temperature
extremes.
Carry fat soluble nutrients
Serve as raw materials.
Provide the major material of which cell
membranes are made.
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Fats
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Provide more energy per gram than
carbohydrate or protein.
Enhance food’s aroma and flavour.
Contributes to tenderness of meats and
baked goods.
Contribute to satiety or a feeling of
fullness after a meal.
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Triglycerides are the body’s chief storage
form of fat.
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Composed of 3 fatty acids and 1
molecule of glycerol. Glycerol is a small
water soluble CHO derivative.
Fatty acids differ in 1) the length of
their carbon chain & 2) the bonding of
carbon atoms and the arrangement of
hydrogen along the carbon chain.
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Fatty Acids
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Short chain fatty acids have 4 to 8
carbons (dairy fats).
Medium chain fatty acids have 8 to 12
carbons (palm oil & coconut oil).
Long chain fatty acids have 16 to 18
carbons (many animal fats).
Diet composed mainly of long chain
fatty acids from animal sources.
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Saturated versus unsaturated
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Saturation refers to the number of hydrogens
a fatty acid chain is holding. If every carbon
atom in the chain has a hydrogen, the chain
is saturated.
A carbon chain with one or more points of
hydrogen atoms missing is unsaturated.
The degree of saturation determines
hardness or softness of fats.
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Unsaturated fats
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One point of unsaturation along carbon chain
= monounsaturated fat, e.g., olive oil.
Two or more points of unsaturation =
polyunsaturated fat e.g., safflower oil.
Animal fats are saturated fats. Palm oil and
coconut oil are saturated vegetable fats.
Other plant oils are unsaturated.
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Phospholipids
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Similar to a triglyceride but has a phosphate
group and choline in place of one of the fatty
acids.
The phosphorus makes it soluble in water and
its fatty acid makes it soluble in fat. Therefore
it can act as an emulsifier and keep the fat
dispersed in water.
Phospholipids are also important in blood
clotting & in the insulating sheath around
nerve fibers.
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Phospholipids
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The best known phospholipid is lecithin.
Lecithin & other phospholipids assist fats to
travel back and forth across the lipid
containing membranes of cells into the
watery fluids on both sides.
They enable fat-soluble substances (vitamins
and hormones) to pass easily in and out of
cells.
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Sterols
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Compounds containing a four-carbon ring
structure with a variety of side chains
attached.
Many important body compounds are sterols.
Cholesterol is “the most famous sterol”.
It is a compound the body makes and uses.
The liver makes about 800-1500 mg of
cholesterol/day.
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Cholesterol is a fatty-like
substance.
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Cholesterol’s harmful effect occurs when it
forms deposits in the artery walls.
Major sources are from animal foods or it is
synthesized by the body.
Egg yolk is a major source of cholesterol.
Saturated fat raises blood cholesterol more
than dietary cholesterol.
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Digestion & Absorption of Fats
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Lipids tend to separate from the watery fluids
of digestion.
Bile from the liver emulsifies lipids.
Enzymes are then able to breakdown lipids to
monoglycerides and fatty acids.
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Chylomicrons
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The class of lipoproteins that transport
lipids from the intestinal cells to the rest
of the body.
The chylomicrons are only 1 of several
clusters of lipids and proteins that are
used as transport vehicles for fats.
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Lipid Transport
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The body makes 4 main types of lipoproteins:
Chylomicrons are the largest and least dense. They
transport mostly triglycerides from the intestine (via
the lymph) to the rest of the body.
Very low-density lipoproteins (VLDL) which
carry triglycerides and other lipids. Made in the liver.
Transports lipids to the tissues.
Low-density lipoproteins (LDL) which are made
from VLDL after they have donated much of their fat
to body cells. Composed primarily of cholesterol.
High-density lipoproteins (HDL) which carry
cholesterol from body cells to the liver. Composed
primarily of protein
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“Good” cholesterol/ “bad”
cholesterol
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LDL’s (bad cholesterol) which carry
almost 50% of total cholesterol has the
greatest affinity for arterial walls.
High LDL is associated with higher risk
of heart attack.
High LDL’s contributes to plaque
formation on artery walls. Hence, “bad.”
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Good cholesterol-HDL protects
against heart disease
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Acts as a scavenger of cholesterol
removing it from arterial wall and
transporting it to liver where it is
incorporated into bile and excreted via
intestines.
Competes with LDL fragment for
receptor sites on arterial wall, thus
blocking entrance of LDL into cell wall.
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Essential Fatty Acids
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The body can synthesize all fatty acids except
these.
These 2 polyunsaturated fatty acids are
required for basic body functions.
Both provide raw materials for hormone-like
substances that regulate: blood pressure,
blood clotting, blood lipids, the immune
response, the inflammation response to injury
and infection & others.
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Essential fatty acids continued
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Serve as structural parts of cell
membranes.
Constitute a major part of lipids in the
brain and nerves.
Are essential to normal growth.
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Essential Fatty Acid
Linoleic Acid - Omega 6
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Sources: leafy vegetables, seeds, nuts,
grains, vegetable oils (corn, safflower,
soybean, cottonseed, sesame, sunflower).
Primary member of omega 6 fatty acid family.
Body can convert linoleic acid to other
members of this family.
Omega 6 play a critical role in the cell
membranes that define and protect each cell
of the body.
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Essential Fatty Acid
Linolenic Acid – Omega 3
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Sources: Fats and oils (canola, soybean,
walnut, wheat germ, margarine made
from canola and soybean oil. Nuts &
seeds (flaxseed, walnuts, soybeans
kernels); shellfish and fish (mackerel,
salmon, bluefish, tuna, mullet, lake
trout & others).
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Linolenic acid- omega 3
continued
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Make up a large portion of the brain’s
cerebral cortex and are required for its
development.
Help to form the eye’s retina and are
required for development of normal
vision.
Are converted to hormone-like
substances that affect the heart and
immune system.
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Processing of fats
Hydrogenation:
 Adding of hydrogen to vegetable oils to
improve shelf life, plasticity
(hardness/spreadability).
 Stability at high temperatures in
cooking.
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Trans fats
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Fatty acids with hydrogens on opposite sides
of the double bond.
They may elevate LDL cholesterol and lower
HDL.
Sources: fast foods, baked goods,
commercially prepared foods, margarines.
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Trans Fats
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Act like saturated fats in the body
Most found in commercially prepared
foods
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some French fries, potato chips,
donuts, cookies, crackers, cereals,
shortening, muffins, pizza crusts, buns,
cakes
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Naturally Occurring Trans Fats
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Found in dairy and meat products
Some are not the same as those
found in processed foods
One type is conjugated linoleic acid
(CLA)
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These may reduce risk of cancer and
heart disease.
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Fat and cardiovascular disease
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High blood cholesterol is a strong risk
factor for heart disease.
Dietary cholesterol has little impact on
blood cholesterol.
Saturated fat significantly increases
blood cholesterol.
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Risk factors for heart disease
Modifiable:
 High cholesterol
 High blood pressure
 Cigarette Smoking
 Obesity
 Diabetes
 Physical Inactivity
Non-Modifiable:
 Increasing age, gender, family history.
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Syndrome X/ Metabolic
Syndrome/Insulin resistance
syndrome
Low HDL, high blood pressure, insulin
resistance and abdominal obesity along
with: high blood triglycerides comprise
a cluster of health risks known as the
metabolic syndrome.
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1990 Nutrition Recommendations
for fat
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No more than 30% of energy as fat.
No more than 10% as saturated fat.
Health Canada recommends an intake
of total omega-3 fatty acids at a level of
at least 0.5% of energy and an intake
of total omega-6 fatty acids of at least
3% of energy.
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Fat replacers
Ingredients that replace some or all of the
functions of fat and may or may not provide
energy.
Conventional ingredients used in different ways:
 Add water or whip air into foods.
 Add fat-free milk to creamy foods.
 Use lean meats and soy protein to replace
high-fat meats.
 Bake foods instead of frying them.
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Artificial fats
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They are fat replacers that offer the sensory
and cooking qualities of fats, but none of the
kcalories.
Olestra appears to have same properties as
fats and oils when used in cooking, frying and
baking and tastes very much like real fat.
Olestra may cause abdominal cramping and
loose stools and inhibits the absorption of
some vitamins and other nutrients.
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Fat - Part of a Healthy Diet
20 – 35% of total Calories from fat
2000 Calorie diet
= 44 – 78 grams of fat
Or 11 – 19 ½ teaspoons.
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1500 Calorie diet
= 33 – 58 grams of fat
Or 8 ¼ – 14 ½ teaspoons.
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Where is fat found?
1. Easy to see
 Fat added to foods
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Butter, margarine, oil
Fat on the outside of foods
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Chicken skin, outside trim on meat
2. Hidden
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Snack foods, baked products, desserts
Added in cooking
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Fried foods, cream soups, sauces
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Types of Fat
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All fat-containing foods have a mixture
of different fats
Types of fats include:
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Polyunsaturated fats (PUFA)
Monounsaturated fats (MUFA)
Saturated fats (SFA)
Trans fats (TFA)
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Nutrition Claims
Nutrient Content Claims
Fat free – none or hardly any fat (less
than 0.5 grams of fat per amount)
Low fat – a small amount (less than
3 grams of fat per amount)
Light – can be used on foods that are
reduced in fat or Calories compared
to the original version
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Nutrition Claims
Health Claim Example:
A healthy diet low in saturated and
trans
fats may reduce the risk of heart
disease.
(Name of food) is low in saturated and
trans fats.
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Ingredient List
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Look for types of fat
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Vegetable oils
Tropical oils (palm, coconut)
Hydrogenated or partially hydrogenated
oils
Shortening or margarine
Animal fats/lard
Butter
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Lower-fat Cooking Tips
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Broil, bake, barbecue, roast, microwave,
stir-fry or brown in a non-stick pan.
Brown ground meat or poultry in a pan
or microwave in a plastic sieve and drain
off fat before adding other ingredients.
Refrigerate stews, soups, chilies and
meat sauces and remove hardened fat
that rises to the surface.
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Recommended
Intakes of Fat
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Linoleic acid AI (omega 6)
 5% - 10% of energy intake
Linolenic acid AI (omega 3)
 0.6 - 1.2% of energy intake
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Copyright 2005 Wadsworth Group, a division of Thomson Learning
Mediterranean Diet
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Diets focus on: crusty breads, whole
grains, potatoes, pastas, variety of
vegetables, legumes, feta and
mozzarella cheeses, yogurt, nuts, fruits.
Fish, seafood, poultry, a few eggs and
little meat is eaten.
Principle sources of fat are olives, olive
oil, nuts and fish.
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Mediterranean Diets are:
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Low in saturated fat.
Very low in trans fat.
Rich in unsaturated fat.
Rich in complex carbohydrate and fibre.
Rich in nutrients and phytochemicals
that support good health.
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