Transcript Triglycerides (cont`d)

Lipids
Chapter 4
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Lipids
• Low-fat diets do not always mean weight loss
• “Good” (unsaturated)
– Eat in moderation
• “Bad” (saturated fat and trans fats)
– Limited
• 3 classes of lipids
– Triglycerides (fats and oils)
– Phospholipids (e.g., lecithin)
– Sterols (e.g., cholesterol)
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Triglycerides
• Approximately 98% of the fat in foods
• Made of the same elements as carbohydrates
– Carbon, hydrogen, and oxygen
– Proportionately more carbon and hydrogen
atoms to oxygen atoms, triglycerides yield
more calories per gram than carbohydrates
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• Fatty acids
Triglycerides (cont’d)
– Basically chains of carbon atoms with hydrogen atoms
attached
– Vary in the length of their carbon chain and in the
degree of unsaturation
– Carbon chain length
o Almost all fatty acids have an even number of
carbon atoms in their chain
o Long-chain fatty acids
o Medium- and short-chain fatty acids
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation
o When all the carbon atoms in a fatty acid have four
single bonds each, the fatty acid is said to be
“saturated” with hydrogen atoms
o An “unsaturated” fatty acid does not have all the
hydrogen atoms it can potentially hold; therefore,
one or more double bonds form between carbon
atoms in the chain
 Monounsaturated
 Polyunsaturated
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Fatty acids can attach to glycerol molecules
o Types and proportions of fatty acids present
influence the sensory and functional
properties of the food fat
o All food fats contain a mixture of saturated,
monounsaturated, and polyunsaturated fatty
acids
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Saturated fats
 Tend to be solid at room temperature
 Animal fats provide approximately 60%
of fat in American diet
 The only vegetable fats that are
saturated are palm oil, palm kernel oil,
and coconut oil
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Saturated fats (cont’d)
 Commonly known as a “bad” fat because it raises
blood cholesterol levels
 Raises total and LDL cholesterol levels
 As levels rise, risk of coronary heart disease rises
 May also make the inner lining of arteries more prone
to inflammation and the buildup of fatty plaques by
interfering with the normal protective action of HDLcholesterol
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats
 Liquid at room temperature
 Monounsaturated fats are the predominant
fat in olives, olive oil, canola oil, peanut oil,
avocado, cashews, almonds, and most other
nuts
 Polyunsaturated fats are the predominant fat
in corn, soybean, safflower, and cottonseeds
oils, and also in fish
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats (cont’d)
 Commonly known as “good fats” because when they
are eaten in place of saturated fats they lower LDLcholesterol and raise HDL-cholesterol
 Position of the double bond
 Part of an unsaturated fatty acid’s identity is
determined by the location of the first or only
double bond along the carbon chain
 Location of first double bond significant
 Determines essentiality of fatty acid
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats (cont’d)
 Linoleic acid
 The essential n-6 fatty acid
 Especially abundant in plant oils
 Alpha-linolenic acid
 The essential n-3 fatty acid
 Found in flaxseed, canola, soybean, and
walnut oils; and in nuts, especially walnuts
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats (cont’d)
 Alpha-linolenic acid (cont’d)
 Can convert alpha-linolenic acid to
eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA) in the body
 Commonly referred to as “fish oils”
 Stability of fats
 Degree of unsaturation influences the stability of
fats
 Polyunsaturated fats are most susceptible to
rancidity
– Food manufacturers may add antioxidants or hydrogenate to
prolong shelf life
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats (cont’d)
 Hydrogenation and trans fats
 Hydrogenation is a process that adds
hydrogen atoms to heart-healthy
polyunsaturated oils to saturate some
of the double bonds so that the
resulting product is less susceptible to
rancidity and has improved function
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats (cont’d)
 Hydrogenation and trans fats (cont’d)
 1970s
 Process of hydrogenation changes the
placement of the hydrogen atoms
 Most trans fat in a typical American diet
comes from partially hydrogenated oils and
foods made with partially hydrogenated oils
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Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d)
o Unsaturated fats (cont’d)
 Hydrogenation and trans fats (cont’d)
 Trans fats, like saturated fat, raise LDLcholesterol and lower HDL-cholesterol
 Ounce for ounce, trans fats are more
unhealthy than saturated fats
 FDA labeling must include trans fats
 Trans fats being eliminated from commercial
use
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Triglycerides (cont’d)
• Functions of triglycerides in the body
– Primary function of fat is to fuel the body
– Other important functions in the body:
o Insulate and cushion internal organs
o Help to regulate body temperature
o Facilitate the absorption of the fat-soluble
vitamins A, D, E, and K when consumed
at the same meal
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Triglycerides (cont’d)
• Functions of triglycerides in the body
(cont’d)
– Essential fatty acids have specific functions
in the body
– Much interest in fish oils
o Results of research inconclusive
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Question
• The process of hydrogenation does what to fats?
a. Makes them into essential fatty acids
b. Changes the placement of the hydrogen
atoms
c. Changes the fats from trans fats to
hydrogenated fats
d. Changes the fats from liquid to solid form
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Answer
b. Changes the placement of the hydrogen
atoms
Rationale: The process of hydrogenation
changes the placement of the hydrogen
atoms around the remaining double bonds
from the natural “cis” position to the rare
“trans” position.
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 Phospholipids
Other Lipids
– Phospholipids have a glycerol backbone with fatty
acids attached like triglycerides
o Difference is phosphate group replaces one of the
fatty acids
– Both fat-soluble (because of the fatty acids) and
water-soluble (because of the phosphate group)
o Enables them to act as emulsifiers
– Structural components of cell membranes that
facilitate the transport of fat-soluble substances across
cell membranes
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Other Lipids (cont’d)
• Phospholipids (cont’d)
– Precursors to prostaglandins
– Lecithin is the best-known phospholipid
o Supplements unnecessary
o Not an essential nutrient
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Other Lipids (cont’d)
 Cholesterol
– A sterol
o Waxy substance whose carbon, hydrogen, and
oxygen molecules are arranged in a ring
– Occurs in the tissues of all animals
o Found in all cell membranes and in myelin
– Found exclusively in animals
o Liver and egg yolks are the richest sources
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Other Lipids (cont’d)
• Cholesterol (cont’d)
– “Good” and “bad” cholesterol refer to the
lipoprotein packages that move cholesterol
through the blood
– Not an essential nutrient
– Dietary cholesterol increases total and LDLcholesterol
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How the Body Handles Fat
• Digestion
– Minimal amount of chemical digestion of fat
occurs in the mouth and stomach through the
action of lingual lipase and gastric lipases
respectively
– Duodenum
o Stimulates the release of the hormone
cholecystokinin
 Stimulates the gallbladder to release bile
 Prepares fat for digestion
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How the Body Handles Fat (cont’d)
• Digestion (cont’d)
– Most fat digestion occurs in the small
intestine
– End products of digestion are absorbed into
intestinal cells
– Small amount is excreted in feces
– Digestion of phospholipids is similar
– Cholesterol does not undergo digestion; it is
absorbed as is
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How the Body Handles Fat (cont’d)
• Absorption
– About 95% of consumed fat is absorbed
– Small fat particles are absorbed directly through the
mucosal cells into capillaries
– Absorption of larger fat particles, namely
monoglycerides and long-chain fatty acids, is more
complex
o Micelles
o Recombine into triglycerides
o Chylomicrons distribute dietary lipids throughout
the body
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How the Body Handles Fat (cont’d)
• Fat catabolism
– Catabolism of fatty acids increases when:
o Carbohydrate intake is inadequate (e.g., while
on a very low-calorie diet)
o Or catabolism of fatty acids is unavailable
(e.g., in the case of uncontrolled diabetes)
– Fatty acids cannot be reassembled to make
glucose
– Inefficient choice of fuel for glucose-dependent
brain cells, nerve cells, and red blood cells
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How the Body Handles Fat (cont’d)
• Fat anabolism
– Most newly absorbed fatty acids recombine with
glycerol to form triglycerides that end up stored
in adipose tissue
– Fat stored in adipose tissue represents the body’s
largest and most efficient energy reserve
– Adipose cells have a virtually limitless capacity to
store fat
– Fat reserves
o 1 pound of fat provides 3,500 calories
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Question
• What happens to the end products of fat
metabolism? They are:
a. Stored in adipose tissue
b. Stored in the liver
c. Absorbed into intestinal cells
d. Absorbed into the bloodstream
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Answer
c. Absorbed into intestinal cells
Rationale: Micelles deliver fat to the intestinal
cells.
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Fat in Foods
• Vital functions of fat
– Imparts its own flavor, from the mild taste of
canola oil and corn oil to the distinctive tastes
of peanut oil and olive oil
– Transfers heat to rapidly cook food, as in the
case of frying
– Absorbs flavors and aromas of ingredients to
improve overall taste
– Adds juiciness to meats
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Fat in Foods (cont’d)
• Vital functions of fat (cont’d)
– Creates a creamy and smooth “mouth feel” in items
such as ice cream, desserts, and cream soups
– Adds texture or body to many foods, such as
flakiness, tenderness, elasticity, and viscosity; for
example, milk is watery and cheese is rubbery
when fat is removed
– Imparts tenderness and moisture in baked goods,
such as cookies, pies, and cakes, and delays staling
– Is insoluble in water, thus providing a unique flavor
and texture to foods such as salad dressings
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Fat in Foods (cont’d)
• Fat content in MyPyramid varies greatly among
groups and between selections within each group
– Generally, three MyPyramid food groups provide
little or no fat
o Grains naturally contain very little fat
o Unadulterated vegetables contain little or no
fat
o Fruits, with the exception of avocado, coconut,
and olives, are naturally fat-free
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Fat in Foods (cont’d)
• Milk
– Classified into one of 3 subgroups: full fat, reduced
fat, and fat free
o Fat in dairy products is predominately saturated
and full-fat products have more cholesterol than in
the lower-fat options
o Fat-free varieties of milk, yogurt, and cheese
provide virtually no fat
o The midrange is reserved for reduced-fat items—
they have some of the fat and cholesterol removed
yet retain some of the “mouth feel” characteristic
of whole milk
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Fat in Foods (cont’d)
• Meat and beans
– 4 subgroups based on fat content
– Details worth noting:
o The 1-oz. size cited in MyPyramid is simply a
reference, not a serving size or a portion size;
typically, a serving size (amount recommended for
a meal) is 3 to 4 oz., and a portion size (amount
actually eaten at one time) may be much larger
o Fat added during cooking, such as frying or basting
with fat, increases the overall fat content and
counts as choices from the Oils group; it is
recommended that meats be prepared by methods
that do not add fat, such as baking, roasting,
broiling, grilling, poaching, or boiling
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Fat in Foods (cont’d)
• Meats and fat content
– Untrimmed meats are higher in fat than leanonly portions
– “Red meats,” namely beef, pork, and lamb, are
higher in saturated fat than the “white meats” of
poultry and seafood
– White poultry meat is lower in fat than dark
meat; removing poultry skin removes significant
fat
– Fat content varies among different cuts of meat.
The leanest cuts are beef loin and round; veal
and lamb from the loin or leg; and pork
tenderloin or center loin chop.
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Fat in Foods (cont’d)
• Meats and fat content (cont’d):
– Beef grades can be used as a guide to fat content
because grades are based largely on the amount of
marbling
– Shellfish are very low in fat but have considerable
cholesterol
– Most wild game is very lean; the fat content in
bison, venison, elk, ostrich, pheasant (without skin),
rabbit, and squirrel ranges from 2 to 5 g per 3-oz.
serving
– Processed meats, such as sausage and hot dogs,
may provide more fat calories than protein calories
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Fat in Foods (cont’d)
• Nuts and fat content:
– Nuts have many healthy attributes; they
contain plant protein, fiber, vitamin E,
selenium, magnesium, zinc, phosphorus,
and potassium, in a low–saturated-fat,
cholesterol-free package
o Nuts’ high-fat content of 13 to 20 g/oz.
comes mostly from monounsaturated
fats and polyunsaturated fats; walnuts
are a rich source of alpha-linolenic acid
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Fat in Foods (cont’d)
• Cholesterol in foods
– Egg yolks have approximately 213 mg of
cholesterol. The cholesterol content of typical
cuts of beef, pork, lamb, and poultry is
generally around 70 mg/3 oz. Veal averages
slightly more at about 90 mg/3 oz. The
exceptions are organ meats, which are very
high in cholesterol. Egg whites, dried peas
and beans, are nuts are cholesterol-free.
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Fat in Foods (cont’d)
• Oils
– Allowances are small
– Some items on the oils list actually are
included in other groups also
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Question
• Is the following statement true or false?
The 1-oz. size of meat noted in MyPyramid
is simply a reference.
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Answer
True.
Rationale: The 1-oz. size cited in MyPyramid is
simply a reference, not a serving size or a
portion size.
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Dietary Reference Intakes
• The issue of how much of each particular type of fat
is needed, how much is optimal, and how much is
too much is complex and in some cases
controversial
• Total fat
– Neither an AI or RDA is set for total fat due to
insufficient data
– An acceptable macronutrient distribution range
(AMDR) is estimated to be 20% to 35% of total
calories for adults
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Dietary Reference Intakes (cont’d)
• Saturated and trans fat
– Additional macronutrient recommendation
issued for both of these fats is that intake
should be as low as possible within the
context of a nutritionally adequate diet
– Neither of these fats needs to be consumed
in the diet
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Dietary Reference Intakes (cont’d)
• Essential fatty acids
– Both an acceptable macronutrient distribution range
and adequate intakes have been set for the essential
fatty acids linoleic acid and alpha-linolenic acid
– AI should not be confused with recommended dietary
allowance
– Essential fatty acid deficiency
o Body cannot make essential fatty acids
o Symptoms of essential fatty acid deficiency include
growth failure, reproductive failure, scaly
dermatitis, and kidney and liver disorders
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Dietary Reference Intakes (cont’d)
• Cholesterol
– The additional macronutrient
recommendation issued for cholesterol
is that intake be as low as possible
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Fat in Health Promotion
• Message to eat less fat was too simplistic
• Type of fat in the diet can affect serum lipids more
than the total amount of fat
• Eat less saturated fat and keep trans fat
consumption as low as possible
– To cut saturated fat intake, experts recommend:
o Limiting meat intake, especially red meat, and
choosing lean varieties
o Reduced- or no-fat dairy products
o Hydrogenated fats should be avoided
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Fat in Health Promotion (cont’d)
• Limit total fat and go for unsaturated fats
– Most effective way to limit total and saturated fat and
increase unsaturated fats may be with a plant-based
diet
• Limit cholesterol
– Cholesterol intake becomes less important when
saturated fat intake is low
• What about “fish oils?”
– American Heart Association suggests healthy people
eat at least 2 servings of fish per week
– Fish oil pills are an alternative source of omega-3 fats
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