Transcript Lecture 3a powerpoint

Ingestion, Digestion, Absorption,
Metabolism, Transport, Excretion
Carbohydrates
Lipids
What happens when we eat?-entry to exit
• Ingestion (I)-food and drink in mouth
• Digestion (D)-breaking to food down to absorbable units
• Absorption (A)-absorbable units cross the gi tract to blood
or lymph
• Transport (T)-movement about the body in blood or lymph
to cells for metabolism
• Metabolism(M)-all the chemical reactions that occur in the
body-more on this later in the course
• Excretion (E)-waste leaves body in urine and faeces
primarily
• Whole idea with IDATME is to get nutrients to where (W)
they are needed, when (W) they are needed, in the form
(F) they are needed and in the quantity (Q) they are
needed-IDATME and WWFQ must be a tightly
choreographed operation or body shuts down
• Remember IDATME
WWFQ
IDATME VIDEO
• https://www.youtube.com/watch?v=08VyJOEcDos
Carbohydrates
Chapter 2
Carbohydrates
• More than just “sugar” and “starch”
• Provide the majority of calories in almost all human diets
• Carbohydrate classifications
– Carbohydrates
o Class of energy-yielding nutrients that contain only
carbon, hydrogen, and oxygen, hence the common
abbreviation of CHO
o CH2O is the basic formula and hence the name
carbohydrate carbo = carbon and hydrate = H2O
o Simple carbohydrates contain only one or two
saccharide units (monosaccharide and
disaccharides). Mono = 1 and di = 2
o Complex carbohydrates contain many saccharide
unit molecules (oligosaccharides (3-10 saccharide
units and polysaccharides (> 10 saccharide units)).
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Monosaccharides-single saccharide
units
o Simplest of all sugars
o Most common
 Glucose
 Fructose
 Galactose
Carbohydrates—(cont.)
Monosaccharides-building blocks of
disaccharides, oligosaccharides and
polysaccharides
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Monosaccharides—(cont.)
o Glucose
 Also known as dextrose
 Component of all disaccharides
 Sugar into which the body converts
all other digestible carbohydrates
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Monosaccharides—(cont.)
o Fructose or “fruit sugar”
 Sweetest of all natural sugars
 High-fructose corn syrup (HFCS)
o Galactose
 Does not occur in appreciable amounts
in foods
 Combines with glucose to form lactose
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Disaccharides
o Made of two linked monosaccharides
o Sucrose, maltose, and lactose are
disaccharides.
 Sucrose or “table sugar”
 Composed of glucose and fructose
 Occurs naturally in some fruits and
vegetables
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Disaccharides—(cont.)
o Maltose
 Composed of two joined glucose molecules
 Not found naturally in foods
 Results from breakdown of starch in humans
o Lactose or “milk sugar”
 Composed of glucose and galactose
 Found naturally in milk
 Least sweet of all sugars
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Disaccharides—(cont.)
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
• Complex carbohydrates
– Oligosaccharides
o 3-10 saccharide units
 Found naturally in foods e.g. beans (e.g.
raffinose and stachyose)
 Some are tough to digest and are passed
to the large intestine where bacteria make
gas, short chain fatty acids and lactic acid
from them
 Are now considered to be dietary fibre
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Polysaccharides
o Complex carbohydrates
o Do not taste sweet
o Starch, glycogen, and fibre are types of
polysaccharides.
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Polysaccharides—(cont.)
o Starch
 Glucose not used by plants stored as starch
 Grains
 World’s major food crops
 Foundation of all diets
 Potatoes, dried peas and beans have
starch
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Polysaccharides—(cont.)
o Glycogen
 Animal (including human) version of
starch
 Liver glycogen releases glucose into the
bloodstream to maintain blood sugar
between meals.
 No dietary source of glycogen
Oligosaccharidespart of fibre
Carbohydrates—(cont.)
• Carbohydrate classifications—(cont.)
– Polysaccharides—(cont.)
o Fibre
 Generally considered a group name for
oligosaccharides and polysaccharides that cannot
be digested by human enzymes
 Commonly referred to as “roughage”
 Categorized as water-insoluble or water-soluble
 Commonly assumed that fibre does not provide any
calories
 However, fibre is broken down by bacteria in the
colon to form short chain fatty acids (acetic,
proprionic and butyric) acids and lactic acid all of
which can be used for energy
 Gases (H2, CO2, CH4) is also formed by bacteria in
the colon
Carbohydrates—(cont.)
• Sources of carbohydrates
– Grains, Vegetables, Fruits, and Dairy are
provide the majority of carbohydrates.
– Nuts and dried peas and beans
– Grains
o Synonymous with “carbs”
o Classified as “whole” or “refined”
Carbohydrates—(cont.)
• Sources of carbohydrates—(cont.)
– Grains—(cont.)
o Whole grains
 Consist of the entire kernel of a grain
 Can be cracked, ground, or milled into flour
 Composed of three parts
 The bran
 The endosperm
 The germ (embryo)
Carbohydrates—(cont.)
• Sources of carbohydrates—(cont.)
– Grains—(cont.)
o “Refined” grains
 Grains rich in starch but as the result of
refining lose fibre, vitamins, trace minerals,
fat, and phytochemicals found in whole grains
so have to be enriched with e.g. folic acid
 Enrichment
 “Enriched” versus “fortified” -enriched
foods have nutrients added back in after
refinement . Fortified foods add more
nutrients to the food, rather than replacing
the removed nutrients.
 Examples include white flour, white bread,
white rice, and refined cornmeal.
Carbohydrates—(cont.)
• Sources of carbohydrates—(cont.)
– Vegetables
o Starch and some sugars provide the
majority of calories in vegetables.
o “Starchy” vegetables provides three times
more carbohydrate than the same
amount of “watery” vegetables.
Carbohydrates—(cont.)
• Sources of carbohydrates—(cont.)
– Fruits
o Almost all of the calories in fruit come from
sugar (mostly fructose), with small
amounts of starch and minute quantities of
protein providing negligible calories.
o Exceptions to this are avocado, olives, and
coconut, which get the majority of their
calories from fat.
o fibre is located in the skin of fruits.
Carbohydrates—(cont.)
• Sources of carbohydrates—(cont.)
– Dairy
o One cup of milk provides 12 g of carbohydrate
in the form of lactose.
o Cottage cheese, which has about 6 g of
carbohydrate per cup
– Empty calories
o e.g. soft drinks
o Carbohydrate content varies
Carbohydrates—(cont.)
• How the body handles carbohydrates
– Digestion
o Cooked starch begins to undergo digestion in the mouth
by the action of salivary amylase.
o Most carbohydrate digestion occurs in the small
intestine.
o Disaccharidase enzymes split disaccharides into
monosaccharides.
o Monosaccharides are the only form of carbohydrates the
body is able to absorb intact.
o Normally, 95% of starch is digested usually within 1 to
4 hours after eating.
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– Absorption
o Monosaccharides are absorbed through
intestinal mucosa cells.
o Undigested starch passes with stools.
o Fibres may impair the absorption of some
minerals—namely, calcium, zinc, and iron—by
binding with them in the small intestine.
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– Metabolism
o Fructose and galactose are converted to glucose
in the liver.
o Liver releases glucose to maintain blood sugar
level.
o Rise in blood sugar causes pancreas to release
insulin.
o Postprandial state
 Blood glucose concentration begins to drop.
 Pancreas releases glucagon.
 Glucagon stimulates liver to release glucose.
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– glycaemic response to foods
o Increase in blood glucose levels
o glycaemic index (GI)
 Determined by comparing the impact on
blood glucose after 50 g of a food sample
is eaten compared to the impact of 50 g
of pure glucose or white bread= GI= 100
 May help diabetics and athletes but is
controversial and not found on food
labels and not all foods have been
assigned a GI value so its current utility
is limited
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– Glycaemic index
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– Glycaemic response to foods
o Glycaemic index
 Whole grain foods have a lower
glycaemic index than white bread
 potato > yam
legumes > root veggies
fruits ~ legumes
 Fruits about equal to milks in GI
(fructose ~ lactose in terms of GI)
 Meats- GI = 0 (no carbs in meat)
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
• Low glycemic index (GI of 55 or less): Most fruits
and vegetables, beans, minimally processed grains,
pasta, low-fat dairy foods, and nuts.
• Moderate glycemic index (GI 56 to 69): White and
sweet potatoes, corn, white rice, couscous, breakfast
cereals such as Cream of Wheat and Mini Wheats.
• High glycemic index (GI of 70 or higher): White
bread, rice cakes, most crackers, bagels, cakes,
doughnuts, croissants, most packaged
breakfast cereals.
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– glycaemic response to foods—(cont.)
o glycaemic load= GI times the carbohydrate
(grams) in food (note grams of carbohydrate
means carbohydrate in food not including
fibre)
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– Glycaemic load
 Not reliable for choosing healthy diet
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
o Glucose metabolism = balance between
catabolism (tear down) and anabolism (build
up)
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
-Functions
of carbohydrates
o Glucose for energy
 Primary function of carbohydrates is to provide
energy for cells.
 Brain is totally dependent on glucose for
energy.
 Spares protein and prevents ketosis
o Protein sparing
 Need to consume adequate carbohydrates
Carbohydrates—(cont.)
• How the body handles carbohydrates—(cont.)
– Functions of carbohydrates—(cont.)
o Preventing ketosis
 Without adequate glucose, fat oxidation
prematurely stops at the intermediate step of
ketone body formation.
 Increased production of ketones causes
nausea, fatigue, loss of appetite, and
ketoacidosis.
 Dehydration and sodium depletion may follow.
Carbohydrates—(cont.)
• Using glucose to make other compounds
– Glycogen
o Body’s backup supply of glucose
o One-third of the body’s glycogen reserve
is in the liver.
– Nonessential amino acids
– Carbohydrate-containing compounds
– Fat
Carbohydrates—(cont.)
• Dietary reference intakes
– Total carbohydrate
o The RDA for carbohydrates is set at 130 g for
both adults and children.
o Acceptable macronutrient distribution range
45-65 % of calories
– Fibre
o Adequate intake for total fibre is set at 14 g/
1000 calories.
– Sugar
o Maximal level of 25% of total calories or less
from added sugars is recommended.
Carbohydrates—(cont.)
However, World Health Organisation indicated on 5
March 2014 that keeping one’s simple sugar (mono
and disaccharides) consumption to less than 5 %
of daily calories (i.e. less than about 6 teaspoons of
sugar) has added health benefits compared to
keeping one’s simple sugar (mono and
disaccharides) consumption than 10 % of calories
(WHO’s previous recommendation).
This refers to all simple sugars whether they are
added (pop, cakes) or naturally (e.g. honey, fruit)
occurring.
Carbohydrates in Health Promotion
• Concentrate on fibre and whole grains
– Most consistent benefit of consuming adequate fibre is
to relieve or prevent constipation.
– Linked to a decreased risk of heart disease, cancer,
diabetes, and obesity
– Dietary guidelines recommend that adults and children
consume at least one-half of their grain servings from
whole grains.
o Results in 20% to 30% lower risk of atherosclerotic
cardiovascular disease
Carbohydrates in Health Promotion—
(cont.)
• Concentrate on fibre and whole grains—(cont.)
– Dietary guidelines—(cont.)
o Less likely to develop insulin resistance and metabolic
syndrome, common precursors of type 2 diabetes
o Associated with improved body weight management
– Tips for choosing whole grains
o Factors contributing to the low intake of whole grains
include consumers’ inability to identify whole grains, a
lack of awareness of their health benefits, cost, taste,
and unfamiliarity with how to prepare whole grains.
Carbohydrates in Health Promotion—
(cont.)
• How to increase dietary fibre
– Replace refined grains with whole grains.
– Choose a ready-to-eat cereal with 5 g of fibre or more
per serving.
– Eat dried peas and beans two to three times per week.
– Eat at least five servings of fruits and vegetables
daily.
– Eat a variety of plant foods daily.
– Increase fibre intake gradually to avoid GI intolerance.
– Consume adequate fluid.
Carbohydrates in Health Promotion—
(cont.)
• Limit added sugars
– Sugar adds flavor and interest.
– Limiting intake is prudent-added sugars
contribute to obesity
– Sugar alternatives
o Sugar alcohols
o Nonnutritive sweeteners (e.g. sucralose
aspartame, saccharin, cyclamate)
Carbohydrates in Health Promotion—
(cont.)
• Limit added sugars—(cont.)
– Sugar alternatives—(cont.)
o Sugar alcohols
 Sorbitol, mannitol, and xylitol
 Natural sweeteners derived from
monosaccharides
 Most are commercially synthesized.
 Incompletely absorbed
 Side effects
 Offer sweetness without promoting cavities
Carbohydrates in Health Promotion—
(cont.)
 Limit added sugars—(cont.)
– Sugar alternatives—(cont.)
o Nonnutritive sweeteners
 Virtually calorie free
 Sweeter than sugar
 Do not raise blood glucose levels
o Risks and benefits of nonnutritive sweeteners
 Weight management
 Diabetes mellitus
 Safety
Carbohydrates in Health Promotion—
(cont.)
• Take steps to avoid dental caries
– Choose between-meal snacks that are healthy
and teeth-friendly.
– Limit between-meal carbohydrate.
– Avoid high-sugar items.
– Brush promptly after eating.
– Chew gum sweetened with sugar alcohols.
– Use fluoridated toothpaste.
Carbohydrates in Health Promotion—
(cont.)
 The most common sources of added
sugars in the Canadian diet
– Soft drinks
– Cakes, cookies, and pies
– Fruit drinks and punches
– Dairy desserts such as ice cream
– Candy
Carbohydrates in Health Promotion—
(cont.)
• Sugar: too much of a good thing
– Behavioral problems in children-false
– Obesity-true
– Diabetes mellitus-type 2-true
– Atherosclerotic heart disease-true
Lipids-Chapter 4
• Low-fat diets do not always mean weight loss.
• “Good” (unsaturated)
– Eat in moderation-too much causes weight gain
• “Bad” (saturated fat and trans fats)
– Limited-note however that now saturated fats are
considered less problematic than before however
recommendation is that dietary saturated fats make
up less than 10 % of daily calories remains
Lipids
• Four classes of lipids
– Fatty acids-mostly attached to triglycerides,
phospholipids and cholesterol though a small pool of
fatty acids are unattached and thus called free fatty
acids
– Triglycerides (fats and oils)-most of the fat in our
diets
– Phospholipids (e.g., lecithin)-least of the fat in our
diets
– Sterols (e.g., cholesterol)-middling amount in our
diets
Fatty acids
– 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 (11 or 13 carbons and
above)
o Medium-(6-10 carbons)(some say 6-12 carbons)
and short-chain (2-4 carbon) fatty acids
Fatty acids—(cont.)
– 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
Fatty acids—(cont.)
o All food fats contain a mixture of saturated,
monounsaturated, and polyunsaturated fatty
acids.
Fatty acids—(cont.)
– Degree of saturation—(cont.)
o Saturated fats
 Tend to be solid at room temperature
 Animal lipids are richer in saturated fats
compared to plant lipids.
 The only vegetable fats that are
saturated are palm oil, palm kernel oil,
and coconut oil.
Fatty acids—(cont.)
– Degree of saturation—(cont.)
o Saturated fats—(cont.)
 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 HDL
cholesterol
Fatty acids—(cont.)
– Degree of saturation—(cont.)
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.
Fatty acids—(cont.)
– Degree of saturation—(cont.)
o Unsaturated fats—(cont.)
 Commonly known as “good fats” because when they
are eaten in place of saturated fats, they lower LDL
cholesterol and raise HDL cholesterol
Fatty acids—(cont.)
– Degree of saturation—(cont.)
o Unsaturated fats—(cont.)
 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
Fatty acids—(cont.)
– Degree of saturation—(cont.)
o Unsaturated fats—(cont.)
 Alpha-linolenic acid—(cont.)
 Can convert alpha-linolenic acid to
eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA) in the body (very inefficient conversion
of 5 % or less) EPA and DHA are in 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. However, hydrogenation can produce
trans fats.
Fatty acids—(cont.)
• Fatty acids—(cont.)
– Degree of saturation—(cont.)
o Unsaturated fats—(cont.)
 Hydrogenation and trans fats
 Hydrogenation is a process that adds hydrogen
atoms to heart healthy polyunsaturated oils to
saturate some or all of the double bonds so that the
resulting product is less susceptible to rancidity.
 If all of the double bonds are saturated get a
saturated fatty acid; if not all of the double bonds
are saturated get trans configuration
 Saturated fats increase the bad cholesterol and
Trans fats increase the bad cholesterol and decrease
the good cholesterol-this is bad news as
hydrogenation process creates clogging of the
arteries with fat.
 Clogging of the arteries is atherosclerosis which
increases the risk of heart attack and stroke.
Cis fats are generally heart healthy while trans fats are
not heart healthy
Fatty acids—(cont.)
• Examples of fatty acids in the next slides
• Designated by carbon number, number of
double bonds (if any) and if double bonds are
present then the position of the first double
bond relative to the methyl end of the fatty
acid
• So 18:0 has eighteen carbons and no double
bonds
• So 18:1 (n-9) or 18:1 w9 has eighteen
carbons and one double bond with the double
bond on carbon 9 and the methyl carbon being
carbon 1
REPLACE WITH FIG 5-2 ACETIC ACID
65
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
Fig. 5-1, p. 140
Triglycerides
• Three (tri) fatty acids attached to a glycerol
backbone (glyceride) and hence the name
triglyceride
• 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 in triglycerides
compared to carbohydrates and thus
triglycerides yield more calories per gram
than carbohydrates
Triglycerides—(cont.)
• Functions of fat 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
Triglycerides—(cont.)
• Functions of fat in the body—(cont.)
– Essential fatty acids have specific functions
in the body.
– Much interest in fish oils (omega 3 fatty
acids (eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA))
o Results of some (not all!!) of the fish
oil research inconclusive- fish oils lower
blood plasma triglyceride concentrations
and platelet reactivity for sure - may
improve insulin sensitivity (efficiency
with which insulin gets glucose into
cells)
 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
Other Lipids—(cont.)
• Phospholipids—(cont.)
– Precursors of prostaglandins
– Lecithin is the best-known
phospholipid.
o Supplements unnecessary
o Not an essential nutrient
Other Lipids—(cont.)
 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.
Other Lipids—(cont.)
• Cholesterol—(cont.)
– “Good” and “bad” cholesterol refer to the
lipoprotein packages that move cholesterol
through the blood.
– Not an essential nutrient
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
How the Body Handles Fat—(cont.)
• Digestion—(cont.)
– 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.
How the Body Handles Fat—(cont.)
• Absorption
– About 95% of consumed fat is absorbed.
- small fat molecules (short chain fatty acids,
medium chain fatty acids, glycerol) go direct
to blood
- larger fat molecules (monoglycerides, long chain
fatty acids) are packaged in chylomicrons
and released into lymph- from the lymph
chylomicrons are passed into the blood to
distribute dietary lipids throughout the body
How the Body Handles Fat—(cont.)
• Fat metabolism (catabolism = tear down)
– 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
How the Body Handles Fat—(cont.)
• Fat anabolism (=build up)
– 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 One pound of fat provides 3500 calories
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
Fat in Foods—(cont.)
• Vital functions of fat—(cont.)
– 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
Fat in Foods—(cont.)
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 with minute
quantities of fat.
Fat in Foods—(cont.)
• Dairy
– Classified into one of three 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.
Fat in Foods—(cont.)
• Protein foods
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.
Fat in Foods—(cont.)
• 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.
Fat in Foods—(cont.)
• Meats and fat content—(cont.)
– 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.
Fat in Foods—(cont.)
• Nuts and fat content
– Nuts have many healthy attributes; they
contain plant protein, fibre, 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.
Fat in Foods—(cont.)
• 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.
Fat in Foods—(cont.)
• Oils
– Allowances are small.
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 nor 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.
Dietary Reference Intakes—(cont.)
• 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.
Dietary Reference Intakes—(cont.)
• 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.
Dietary Reference Intakes—(cont.)
• Cholesterol
– Maximum of 300 mg/day of dietary
cholesterol for healthy adults
– Dietary cholesterol has little impact on
blood cholesterol levels
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.
Fat in Health Promotion—(cont.)
• 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 two servings of fish per week. Oily fish like
salmon, anchovies, trout and mackerel are best
choices
– Fish oil pills are an alternative source of omega-3 fats.