Transcript nutrition, metabolism, and body temperature regulation

NUTRITION, METABOLISM,
AND
BODY TEMPERATURE
REGULATION
NUTRITION
• A nutrient is a substance in food that is used by the
body to promote normal growth, maintenance, and
repair
– Some nutrients are used to build cell structures, replace wornout parts, and synthesize functional molecules
– Most nutrients are used as metabolic fuel
• They are oxidized and transformed to ATP, the chemical energy
form used by cells
• The energy value of foods is measures in
kilocalories (kcal) (large calories) ( C )
– One kilocalorie is the amount of heat energy needed to raise
the temperature of 1 kilogram of water 1o C (1.8o F) and is then
unit conscientiously counted by dieters
NUTRITION
• There are six categories of nutrients:
carbohydrates, lipids, proteins, vitamins,
minerals, and water
• Essential nutrients are those that
cannot be made by the body and must
be obtained in the diet
Food Groups
• A diet consisting of
foods from each of the
five food groups:
normally guarantees
adequate amounts of all
the needed nutrients
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Grains
Fruits
Vegetables
Meats
Fish
Milk products
FOOD PYRAMID
New/Old Food Pyramid
New Food Pyramid
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The Food Guide Pyramid is one way for people to understand how to
eat healthy. A rainbow of colored, vertical stripes represents the five
food groups plus fats and oils. Here's what the colors stand for:
orange - grains
green - vegetables
red - fruits
yellow - fats and oils
blue - milk and dairy products
purple - meat, beans, fish, and nuts
The U.S. Department of Agriculture (USDA) changed the pyramid in spring
2005 because they wanted to do a better job of telling Americans how to be
healthy. The agency later released a special version for kids. Notice the girl
climbing the staircase up the side of the pyramid? That's a way of
showing kids how important it is to exercise and be active every day. In
other words, play a lot! The steps are also a way of saying that you can
make changes little by little to be healthier. One step at a time, get it?
Orange/Grains
Orange
Grains (Whole/Refined)
• What foods are in the grain group?
Any food made from wheat, rice, oats, cornmeal, barley or another
cereal grain is a grain product. Bread, pasta, oatmeal, breakfast
cereals, tortillas, and grits are examples of grain products.
Grains are divided into 2 subgroups, whole grains and refined
grains.
Whole grains contain the entire grain kernel -- the bran, germ, and
endosperm.
• Examples include:
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whole-wheat flour
bulgur (cracked wheat)
oatmeal
whole cornmeal
brown rice
Orange
Grains (Whole/Refined)
• Refined grains have been milled, a process that removes the
bran and germ. This is done to give grains a finer texture and
improve their shelf life, but it also removes dietary fiber, iron,
and many B vitamins.
• Some examples of refined grain products are:
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white flour
degermed cornmeal
white bread
white rice
• Most refined grains are enriched. This means certain B vitamins
(thiamin, riboflavin, niacin, folic acid) and iron are added back after
processing. Fiber is not added back to enriched grains. Check the
ingredient list on refined grain products to make sure that the word
“enriched” is included in the grain name.
• Some food products are made from mixtures of whole grains
and refined grains.
Green/Vegetables
Green Column
Vegetable
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What foods are in the vegetable group?
Any vegetable or 100% vegetable juice counts as a member of the
vegetable group. Vegetables may be raw or cooked; fresh, frozen, canned,
or dried/dehydrated; and may be whole, cut-up, or mashed.
Vegetables are organized into 5 subgroups, based on their nutrient
content. Some commonly eaten vegetables in each subgroup are:
Dark green vegetables:
bok choy
broccoli
collard greens
dark green leafy lettuce
kale
mesclun
mustard greens
romaine lettuce
spinach
turnip greens
watercress
Green Column
Vegetable
• Dry beans and peas
• black beans
black-eyed peas
garbanzo beans (chickpeas)
kidney beans
lentils
lima beans (mature)
navy beans
pinto beans
soy beans
split peas
tofu (bean curd made from soybeans)
white beans
Green Column
Vegetable
• Orange vegetables
• acorn squash
butternut squash
carrots
hubbard squash
pumpkin
sweetpotatoes
Green Column
Vegetable
• Starchy vegetables
• corn
green peas
lima beans (green)
potatoes
Green Column
Vegetable
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Other vegetables
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artichokes
asparagus
bean sprouts
beets
Brussels sprouts
cabbage
cauliflower
celery
cucumbers
eggplant
green beans
green or red peppers
iceberg (head) lettuce
mushrooms
okra
onions
parsnips
tomatoes
tomato juice
vegetable juice
turnips
wax beans
zucchini
Red/Fruit
Red/Fruit
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What foods are in the fruit group?
Any fruit or 100% fruit juice counts as part of the fruit group. Fruits may be
fresh, canned, frozen, or dried, and may be whole, cut-up, or pureed. Some
commonly eaten fruits are:
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Apples
Apricots
Avocado
Bananas
Berries:
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strawberries
blueberries
raspberries
cherries
Red/Fruit
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Grapefruit
Grapes
Kiwi fruit
Lemons
Limes
Mangoes
Melons:
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cantaloupe
honeydew
watermelon
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Mixed fruits:
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fruit cocktail
Red/Fruit
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Nectarines
Oranges
Peaches
Pears
Papaya
Pineapple
Plums
Prunes
Raisins
Tangerines
100% Fruit juice:
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orange
apple
grape
grapefruit
Yellow/Oil
Yellow/Oil
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Oils are fats that are liquid at room temperature, like the vegetable oils
used in cooking. Oils come from many different plants and from fish.
Some common oils are:
canola oil
corn oil
cottonseed oil
olive oil
safflower oil
soybean oil
sunflower oil
Some oils are used mainly as flavorings, such as walnut oil and sesame oil.
A number of foods are naturally high in oils, like:
nuts
olives
some fish
avocados
Yellow/Oil
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Foods that are mainly oil include mayonnaise, certain salad dressings, and soft (tub or squeeze)
margarine with no trans fats. Check the Nutrition Facts label to find margarines with 0 grams of
trans fat. Amounts of trans fat will be required on labels as of 2006. Many products already
provide this information.
Most oils are high in monounsaturated or polyunsaturated fats, and low in saturated fats. Oils from
plant sources (vegetable and nut oils) do not contain any cholesterol. In fact, no foods from
plants sources contain cholesterol.
A few plant oils, however, including coconut oil and palm kernel oil, are high in saturated
fats and for nutritional purposes should be considered to be solid fats.
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Solid fats are fats that are solid at room temperature, like butter and shortening. Solid fats come
from many animal foods and can be made from vegetable oils through a process called
hydrogenation. Some common solid fats are:
butter
beef fat (tallow, suet)
chicken fat
pork fat (lard)
stick margarine
shortening
Light Blue/Milk
Light Blue/Milk
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What foods are included in the milk, yogurt, and cheese (milk) group?
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All fluid milk products and many foods made from milk are considered part of
this food group. Foods made from milk that retain their calcium content are part of
the group, while foods made from milk that have little to no calcium, such as cream
cheese, cream, and butter, are not. Most milk group choices should be fat-free or lowfat.
Some commonly eaten choices in the milk, yogurt, and cheese group are:
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Milk*
All fluid milk:
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fat-free (skim)
low fat (1%)
reduced fat (2%)
whole milk
Light Blue/Milk
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flavored milks:
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chocolate
strawberry
lactose reduced milks
lactose free milks
Milk-based desserts*
Puddings made with milk
ice milk
frozen yogurt
ice cream
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Cheese*
Hard natural cheeses:
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cheddar
mozzarella
Swiss
parmesan
soft cheeses
Light Blue/Milk
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ricotta
cottage cheese
processed cheeses
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American
Yogurt*
All yogurt
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Fat-free
low fat
reduced fat
whole milk yogurt
*Selection Tips
Choose fat-free or low-fat milk, yogurt, and cheese. If you choose milk or yogurt that is not fat-free, or cheese that
is not low-fat, the fat in the product counts as part of the discretionary calorie allowance.
If sweetened milk products are chosen (flavored milk, yogurt, drinkable yogurt, desserts), the added sugars also
count as part of the discretionary calorie allowance.
For those who are lactose intolerant, lactose-free and lower-lactose products are available. These include hard
cheeses and yogurt. Also, enzyme preparations can be added to milk to lower the lactose content. Calciumfortified foods and beverages such as soy beverages or orange juice may provide calcium, but may not provide
the other nutrients found in milk and milk products.
Purple/Meat-Bean
Purple/Meat-Beans
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What foods are included in the meat, poultry, fish, dry beans, eggs, and nuts (meat & beans) group?
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All foods made from meat, poultry, fish, dry beans or peas, eggs, nuts, and seeds are considered part of this
group. Dry beans and peas are part of this group as well as the vegetable group. For more information on dry
beans and peas click here.
Most meat and poultry choices should be lean or low-fat. Fish, nuts, and seeds contain healthy oils, so choose
these foods frequently instead of meat or poultry. (See Why is it important to include fish, nuts, and seeds?)
Some commonly eaten choices in the Meat and Beans group, with selection tips, are:
What's in the Meat & Beans Group? How much is needed? What counts as an ounce?
and health implications Tips for making wise choices Vegetarian Choices
Grains
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Vegetables
Fruits
Milk
Meat & Beans
Oils
Discretionary Calories
Nutrients
Physical Activity
Purple/Meat-Beans
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Meats*
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Lean cuts of:
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beef
ham
lamb
pork
veal
Game meats:
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bison
rabbit
venison
Lean ground meats:
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beef
pork
lamb
Lean luncheon meats
Organ meats:
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liver
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giblets
Purple/Meat-Beans
• Poultry*
• chicken
duck
goose
turkey
ground chicken and turkey
Eggs*
• chicken eggs
duck eggs
Purple/Meat-Beans
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Dry beans and peas:
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black beans
black-eyed peas
chickpeas (garbanzo beans)
falafel
kidney beans
lentils
lima beans (mature)
navy beans
pinto beans
soy beans
split peas
tofu (bean curd made from soy beans)
white beans
bean burgers:
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garden burgers
veggie burgers
tempeh
texturized vegetable protein (TVP)
Purple/Meat-Beans
• Nuts & seeds*
• almonds
cashews
hazelnuts (filberts)
mixed nuts
peanuts
peanut butter
pecans
pistachios
pumpkin seeds
sesame seeds
sunflower seeds
walnuts
Purple/Meat-Beans
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Fish*
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Finfish such as:
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catfish
cod
flounder
haddock
halibut
herring
mackerel
pollock
porgy
salmon
sea bass
snapper
swordfish
trout
tuna
Purple/Meat-Beans
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Shellfish such as:
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clams
crab
crayfish
lobster
mussels
octopus
oysters
scallops
squid (calamari)
shrimp
Canned fish such as:
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anchovies
clams
tuna
sardines
Purple/Meat-Beans
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*Selection Tips
Choose lean or low-fat meat and poultry. If higher fat choices are made, such as
regular ground beef (75 to 80% lean) or chicken with skin, the fat in the product
counts as part of the discretionary calorie allowance. Click here for more details on
discretionary calories.
If solid fat is added in cooking, such as frying chicken in shortening or frying eggs in
butter or stick margarine, this also counts as part of the discretionary calorie
allowance. Click here for more details on discretionary calories.
Select fish rich in omega-3 fatty acids, such as salmon, trout, and herring, more
often (See Why is it important to include fish, nuts, and seeds?).
Liver and other organ meats are high in cholesterol. Egg yolks are also high in
cholesterol, but egg whites are cholesterol-free.
Processed meats such as ham, sausage, frankfurters, and luncheon or deli
meats have added sodium. Check the ingredient and Nutrition Facts label to help
limit sodium intake. Fresh chicken, turkey, and pork that have been enhanced with a
salt-containing solution also have added sodium. Check the product label for
statements such as “self-basting” or “contains up to __% of __”, which mean that a
sodium-containing solution has been added to the product.
Sunflower seeds, almonds, and hazelnuts (filberts) are the richest sources of vitamin
E in this food group. To help meet vitamin E recommendations, make these your nut
and seed choices more often.
Physical Activity
Physical Activity
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Physical activity simply means movement of the body that uses energy. Walking, gardening, briskly pushing a
baby stroller, climbing the stairs, playing soccer, or dancing the night away are all good examples of being active.
For health benefits, physical activity should be moderate or vigorous and add up to at least 30 minutes a day.
Moderate physical activities include:
Walking briskly (about 3 ½ miles per hour)
Hiking
Gardening/yard work
Dancing
Golf (walking and carrying clubs)
Bicycling (less than 10 miles per hour)
Weight training (general light workout)
Vigorous physical activities include:
Running/jogging (5 miles per hour)
Bicycling (more than 10 miles per hour)
Swimming (freestyle laps)
Aerobics
Walking very fast (4 ½ miles per hour)
Heavy yard work, such as chopping wood
Weight lifting (vigorous effort)
Basketball (competitive)
Some physical activities are not intense enough to help you meet the recommendations. Although you are moving,
these activities do not increase your heart rate, so you should not count these towards the 30 or more minutes a
day that you should strive for. These include walking at a casual pace, such as while grocery shopping, and doing
light household chores.
NUTRITION
• The ability of cells, especially those of the
liver, to convert one type of molecules to
another is truly remarkable
– These interconversions allow the body to
use the wide range of chemicals found in
foods and to adjust to varying food intakes
• But there are limits to these conversions:
– At least 45-50 molecules, called essential nutrients,
cannot be made by the body and so must be provided by
the diet
CARBOHYDRATES
Dietary Sources
• Except for milk sugar (lactose) and small amounts of
glycogen found in meats, all the carbohydrates we
ingest are derived from plants
• Sugars (monosaccharides and disaccharides) come
from fruits, sugar cane, sugar beets, honey, and milk
• Polysaccharide starch is found in grains, legumes, and
root vegetables
• Cellulose, a polysaccharide plentiful in most vegetables,
is not digested by humans but provides roughage, or
fiber, which increases the bulk of the stool and facilitates
defecation
CARBOHYDRATES
Uses in the Body
• Glucose (monosaccharide) is the
carbohydrate molecule ultimately used by
the body as fuel to make ATP
– Carbohydrate digestion also yields fructose and
galactose, but these monosaccharides are converted
to glucose by the liver before they enter the general
circulation
• Any glucose in excess of what the body
needs for ATP synthesis is converted to
glycogen or fat and stored for later use
• Pentose (monosaccharides) are used to
synthesize nucleic acids
CARBOHYDRATES
Dietary Requirements
• The current recommendation is 125-175
grams of carbohydrates daily with the
emphasis on complex carbohydrates (whole
grains and vegetables)
– When less than 50 grams per day is consumed,
tissue proteins and fats are used for energy fuel
• Starchy foods and milk have many valuable
nutrients, such as vitamins and minerals
– Refined carbohydrates (sugary foods and soft drinks)
provide energy sources only—the term “empty
calories” is commonly used to describe such food
• Excess stored as fat (obesity)
LIPIDS
Dietary Sources
• The most common dietary lipids are the neutral fats,
triglycerides or triacylglycerols, which occur as saturated fats
and unsaturated fats
– Compounds of higher fatty acids (molecular mass: e.g., oleic) with
glycerol
– They are the common fats of animal and plant tissue
– Known as oils when liquid
• Saturated fats (single bonds): animal products such as meat and
dairy foods and in a few plant products such as coconut
• Unsaturated fats are present in seeds, nuts, and most vegetable
oils
• Fats are digested to fatty acids and monoglycerides and then
reconverted to triglycerides for transport in the lymph
• Cholesterol is another dietary lipid that is found in egg yolk, meats,
and milk products
LIPIDS
LIPIDS
Dietary Sources
• Although the liver is adapt at
converting one fatty acid to another, it
cannot synthesize linoleic or linolenic
acids
– These are essential fatty acids that must
be ingested
• Found in most vegetable oils
LIPIDS
Uses in the Body
• Dietary fats are essential as the major
source of fuel for hepatocytes (liver cell)
and skeletal muscle, for absorption of fatsoluble vitamins, and as components
(phospholipids) of the myelin sheaths and
cellular membranes of the body
LIPIDS
LIPIDS
Uses in the Body
• Fatty deposits in adipose tissue
provide:
– 1. A protective cushion around body organs
– 2. An insulating layer beneath the skin
– 3. An easy-to-store concentrated source of
energy fuel
LIPIDS
Uses in the Body
• Unlike neutral fats, cholesterol is not
used for energy:
– It is important as a stabilizing component
of plasma membranes and is the precursor
from which bile salts, steroid hormones,
and other essential molecules are formed
LIPIDS
Dietary Requirements
• Represents over 40% of the calories in the
typical American diet
– Diet high in saturated fats and cholesterol may
contribute to cardiovascular disease
• American Heart Association suggest:
– 1. Fats should represent 30% or less of total caloric
intake
– 2. Saturated fats should be limited to 10% or less of
total fat intake
– 3. Daily cholesterol intake should be no more than
200 mg (amount in one egg yolk)
Fat Substitutes
• In an attempt to reduce fat intake without
losing fat’s appetizing aspects, many people
have turned to fat substitutes or foods
prepared with them:
– Perhaps the oldest fat substitute is air (beaten into a
product to make it fluffy)
• Soft ice cream
• Most fat substitutes have two drawbacks:
– 1. They don’t stand up to the intense heat needed to
fry foods
– 2. They do not taste nearly as good as the real fat
PROTEINS
Dietary Sources
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Animal products contain the highestquality proteins, those with the greatest
amount and best ratio of essential amino
acids
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Legumes (beans and peas), nuts, and
cereals are protein-rich but their proteins
are nutritionally incomplete because they
are low in one or more of the essential
amino acids
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Proteins in eggs, milk, and most meats are
considered to be complete proteins that meet
all the body’s amino acid requirements for
tissue maintenance and growth
Leafy green vegetables are well balanced in
all essential amino acids except methionine,
but contain only small amounts of protein
Strict vegetarians must carefully plan
their diets to obtain all the essential
amino acids and prevent protein
malnutrition
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When cereal grains and legumes (Mexican
restaurant:rice and beans) are ingested
together they provide all the essential
amino acids
ESSENTIAL AMINO ACIDS
PROTEINS
Uses in the Body
• Proteins are important as structural materials of the body
(keratin, collagen and elastin in connective tissue, and muscle
proteins), enzymes, and hormones
• Whether amino acids are used to synthesize new proteins or
are burned for energy depends on a number of factors:
– 1.The all-or-none rule:
• All amino acids needed to make a particular protein must be present in a cell
at the same time and in sufficient amounts for the protein to be made
• If one is missing, the protein cannot be made
• Because essential amino acids cannot be stored, those not used
immediately to build proteins are oxidized for energy or converted to
carbohydrates or fats
– 2.Adequacy of caloric intake:
• For optimal protein synthesis the diet needs sufficient carbohydrate or fat
calories for ATP production
• When it doesn’t dietary and tissue proteins are used fro energy
PROTEINS
Uses in the Body
– 3.Nitrogen balance:
• In healthy adults the rate of protein synthesis equals the rate of protein
breakdown and loss
– The body is in nitrogen balance when the amount of nitrogen ingested in proteins
is equal to the amount lost in urine and feces
– Positive nitrogen balance: amount of protein being incorporated into tissue is
greater than the amount being broken down and used for energy
» Growing children
» Pregnant women
» Tissue repair following injury or illness
– Negative nitrogen balance: protein breakdown for energy exceeds the amount of
protein being incorporated into tissues
» Physical stress
» Emotional stress
» During infection, injury, burns
» When quality of dietary protein is poor
» Starvation
– 4.Hormonal controls:
• Anabolic hormones accelerate protein synthesis and growth
• The effects of these hormones vary continually throughout life
PROTEINS
Dietary Requirements
• Besides supplying essential amino acids,
dietary proteins furnish the raw materials for
making nonessential amino acids and
various nonprotein nitrogen-containing
substances
• The amount of protein a person needs reflects
his or her age, size, metabolic rate, and current
state of nitrogen balance
– Nutritionists recommend a daily intake of 0.8 g per
kilogram of body weight (0.3 ounces per 2.2 pounds)
– Most Americans eat far more protein than they
need
VITAMINS
• Vitamins are potent organic compounds needed in
minute (small) amounts for growth and good health
– Unlike other organic nutrients, vitamins are not used for
energy and do not serve as building blocks, but they are
crucial in helping the body use those nutrients that do
• Most function as coenzymes or parts of coenzymes
– Act with an enzyme to accomplish a particular chemical task
• Example: B vitamins riboflavin and niacin act as coenzymes in the
oxidation of glucose for energy
• Without vitamins, all the carbohydrates, proteins,
and fats we eat would be useless
VITAMINS
• Most vitamins are not made in the body
– They must be taken in via foods or vitamin supplements:
• Exceptions:
– Vitamin D made in the skin
– Vitamin K synthesized by intestinal bacteria
– Body can convert beta-carotene (provitamin), the orange pigment in
carrots and other foods, to vitamin A
• Found in all major foods, but no one food contains
all the required vitamins
– Thus, a balanced diet is the best way to ensure a full vitamin
complement
• Were given a letter designation that indicated the
order of their discovery
– Today, a more chemical descriptive name has been
assigned
VITAMINS
• Water-soluble vitamins (B complex vitamins and
vitamin C) are absorbed along with water from the
gastrointestinal tract:
– Exception: vitamin B12, which must bind to gastric intrinsic factor
(also needed to produce mature erythrocytes) to be absorbed
• The only stomach function essential for life
• Gastrectomy (stomach removal): vitamin B12 administered by
injection
• Because only insignificant amounts of water-soluble
vitamins are stored in the body, any ingested
amounts not used within an hour or so are excreted
in urine
– Few conditions resulting from excessive levels of these vitamins
(hypervitaminosis) are known
VITAMINS
• Fat-soluble vitamins (A, D, E, and K) bind to ingested
lipids and are absorbed along with their digestion
products
– Anything that interferes with fat absorption also interferes
with the intake of fat-soluble vitamins
• Except for vitamin K, fat-soluble vitamins are stored in the
body:
– Fat-soluble vitamin toxicity (hypervitaminosis) has been documented
» Vitamin A: nausea, vomiting, anorexia (loss of appetite),
headache, hair loss, bone and joint pain, bone fragility,
enlargement of liver and spleen
» Vitamin D: toxic, vomiting, diarrhea, fatigue, weight loss,
hypercalcemia (excess calcium in blood) and calcification of soft
tissue, irreversible cardiac and renal damage
» Vitamin E: slow wound healing, decreased platelet adhesion,
increased clotting time
» Vitamin K: not known because not stored in appreciable amounts
VITAMINS
• Metabolism uses oxygen, and during
these reactions some potentially
harmful free radicals are generated
– Vitamins A, C, and E are antioxidants that
disarm tissue-damaging free radicals and
thereby appear to have anticancer effects
• Good sources of A and C:
– Broccoli, cabbage, cauliflower, and brussels sprouts
MINERALS
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The body requires moderate amounts of seven minerals (calcium,
phosphorus, potassium, sulfur, sodium, chlorine, magnesium) and
trace amounts of about a dozen (fluorine, cobalt, chromium, copper,
iodine, iron, manganese, selenium, zinc) others that are used by the
body to add strength to structures or to act as ions in the blood and
cells
Not used for fuel but work with other nutrients to ensure a smoothly
functioning body
Incorporation of minerals into structures give added strength:
– Calcium, phosphorus, and magnesium salts harden the teeth and strengthen
the skeleton
– Most are ionized in body fluids or bound to organic compounds to form
phospholipids (lipid portion of cell membrane), hormones, enzymes, and
other functional proteins (Fe bound to heme)
– Sodium and chloride ions are the major electrolytes in blood
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A fine balance between uptake and excretion is crucial for retaining
needed amounts of minerals while preventing toxic overload
The most mineral rich foods are vegetables, legumes, milk, and some
meats
METABOLISM
• Once inside body cells, nutrients become
involved in an incredible variety of biochemical
reactions known as metabolism
• Overview of Metabolic Processes:
– Anabolism (building up) is the general term for all
reactions in which larger molecules or structures are
built from smaller ones
• Example: synthesis of proteins from amino acids
– Catabolism degradation, tearing down) refers to all
processes that break down complex structures to
simpler ones
• Example: hydrolysis of food
The three stages of metabolism of energycontaining nutrients in the body
METABOLISM
• In oxidation-reduction reactions one substance is oxidized and
loses energy by losing electrons, while another substance is
reduced and gains energy and electrons that are transferred
from the oxidized substance:
– Oxidation: always loses (or nearly loses) electrons as they move to (or
toward) a substances that more strongly attracts them
• Loss of electrons or,
• Gain of oxygen (when oxygen binds with other atoms the shared electrons
spend more time in oxygen’s vicinity; the molecule as a whole loses
electrons) or,
• Loss of hydrogen atoms (electron goes with it; the molecule as a whole
loses electrons)
• Essentially all oxidation of food involves the step-by-step removal of pairs of
hydrogen atoms (pairs of electrons) from the substrate molecules, eventually
leaving only carbon dioxide (CO2)
– Molecular oxygen (O2) is the final electron acceptor
» It combines with the removed hydrogen atoms at the very end of the
process, to form water (H2O)
METABOLISM
• Whenever one substance loses electrons (oxidized),
another substance gains electrons (reduced)
– Oxidation and reduction are coupled reactions (oxidationreduction reactions—redox reactions)
– The key understanding about redox reactions is that “oxidized”
substances lose energy and “reduced” substances gain
energy as energy-rich electrons are transferred from the former
to the latter
– As foods are oxidized, their energy is transferred to a “bucket
brigade” of other molecules and ultimately to ADP to form
energy-rich ATP
– Redox reactions are catalyzed by enzymes:
• Dehydrogenases: catalyze removal of hydrogen
• Oxidases: catalyze the transfer (acceptance) of oxygen
METABOLISM
• Although the enzyme catalyze the removal of
hydrogen atoms to oxidize a substance, they
cannot accept the hydrogen (hold on or bond
to it)
– Their coenzyme, however, act as hydrogen
(electron) acceptors, becoming reduced each time
a substrate is oxidized
• Two very important coenzymes:
– Nicotinamide adenine dinucleotide (NAD+)
» Based on niacin (a B vitamin)
– Flavin adenine dinucleotide (FAD)
» Derived from riboflavin (a B vitamin)
» Oxidized form
REDOX REACTION
• The oxidation of succinic acid to fumaric
acid and the simultaneous reduction of
FAD to FADH2, an example of a coupled
redox reaction
Mechanisms of ATP Synthesis
•
Our cells use two mechanisms to
capture some of the energy
liberated through oxidationreduction reactions to make ATP:
– 1.Substrate-level
phosphorylation occurs when
high-energy phosphate groups are
transferred directly from
phosphorylated substrates
(metabolic intermediates such as
glyceraldehyde phosphate) to
ADP
• Essentially, this process
occurs because the highenergy bonds attaching the
phosphate groups to the
substrates are even more
unstable than those in ATP
MECHANISM OF
PHOSPHORYLATION
Sites of ATP formation during
cellular respiration
Mechanisms of ATP Synthesis
• 2.Oxidative phosphorylation is carried out by
electron transport, which occurs in the cristae of the
mitochondria and couples the movement of
substances across membranes to chemical
reactions
– An example of chemiosmotic process:
• Couple the movement of substances across membranes to
chemical reactions
• Some of the energy released during the oxidation of food is used to
pump protons (H+) across the cristae membrane into the
intermembrane space
• This creates a steep diffusion gradient for protons across the
membrane
• Then, when H+ does flow back across the membrane (through a
membrane channel protein called ATP synthase), some of this
gradient energy is captured and used to attach phosphate groups to
ADP
MECHANISM OF
PHOSPHORYLATION
Sites of ATP formation during
cellular respiration
Carbohydrate Metabolism
• Because all food carbohydrates are eventually transformed to
glucose, the story of carbohydrates metabolism is really of
glucose metabolism
• Glucose enters the tissue cells by facilitated diffusion, a
process that is greatly enhanced by insulin
• Immediately upon entry into the cell, glucose is phosphorylated to
glucose-6-phosphate by transfer of a phosphate group to its sixth
carbon during a coupled reaction with ATP
– Glucose + ATP → glucose-6-PO4 + ADP
• Because glucose-6-phosphate is a different molecule from
simple glucose, the reaction also keeps intracellular glucose
levels low, maintaining a diffusion gradient for glucose entry
Carbohydrate Metabolism
• Glucose is catabolized via
the reaction:
• C6H12O6 + 6O2 → 6H2O +
6CO2 + 36ATP + HEAT
• Glucose breakdown involves
3 pathways:
• 1.Glycolysis:color-coded light
orange
• 2.The Krebs Cycle: colorcoded pale-green
• 3.The electron transport
chain and oxidative
phosphorylation: color-coded
violet
The three stages of metabolism of energycontaining nutrients in the body
Sites of ATP formation during
cellular respiration
Glycolysis
• A series of ten steps
where glucose is
converted into two
pyruvic acid
molecules in the
cytosol of cells
• Anaerobic process
(does not use oxygen
and occurs whether
or not oxygen is
present)
Glycolysis
•
•
Three major phases:
1.Sugar activation:
– Glucose is phosphorylated and
converted to fructose-6phosphate, which is then
phosphorylated again
• Yields frucrose-1,6-bisphosphate
• These two reactions provide the
activation energy needed to prime
the later stages of the pathway
• Energy investment phase: uses 2
ATP
•
2.Sugar cleavage:
– Frucrose-1,6-bisphosphate is split
into 3-carbon fragments
• Existing as one of two isomers:
– Glyceraldehyde 3-phosphate
– Or
– Bishydroxyacetone phospahte
Glycolysis
•
3.Oxidation and ATP formation:
– Six steps with two major events
• 1.Formation of NADH+H+
(Nicotinamide adenine
dinucleotide)
• 2.Inorganic phosphate groups (Pi)
are attached to each oxidized
fragment by high-energy bonds
•
Final Product:
– Two molecules of pyruvic acid and
two molecules of reduced NAD+
(NADH + H+)
– Net gain of two ATP molecules per
glucose molecule
• 4 ATPs are produced, but
remember that 2 are consumed in
phase 1
THREE MAJOR PHASES OF
GLYCOLYSIS
Glycolysis
•
•
When oxygen is readily available, NADH
+ H+ delivers its burden of hydrogen
atoms to the enzymes of the electron
transport chain in the mitochondria,
which deliver them to O2, forming water
However, when oxygen is not present in
sufficient amounts, as might occur during
strenuous exercise, NADH + H+ unloads its
hydrogen atoms back onto pyruvic acid, thus
reducing it
– This addition of two hydrogen atoms to
pyruvic acid yields lactic acid, some of
which diffuses out of the cells and is
transported to the liver (converting it to
glucose and storing it or releasing it to
the blood)
– When oxygen is again available, lactic
acid is oxidized back to pyruvic acid
and enters the aerobic pathways
(Krebs cycle and electron transport
chain within the mitochondria), and is
completely oxidized to water and
carbon dioxide
THREE MAJOR PHASES OF
GLYCOLYSIS
Krebs Cycle
•
•
•
Occurs in the matrix (fluid portion) of the
mitochondria where the pyruvic acid is
passed through a series of reactions that
generate reduced electron carrier
molecules, NADH + H+ and FADH2
Fueled largely by pyruvic acid production
during glycolysis and by fatty acids resulting
from fat breakdown
After pyruvic acid enters the mitochondria, it
is converted to acetyl CoA (coenyzme A:
sulfur containing coenzyme derived from
pantothenic acid, a B vitamin) via three-step
process
–
–
–
1.Decarboxylation: one of pyruvic acid’s
carbons is removed and released as carbon
dioxide gas (diffuses into the blood and is
expelled by the lungs)
2.Oxidation: removal of hydrogen atoms
which are picked up by NAD+ (Nicotinamide
adenine dinucleotide)
3.Combination of the resulting acetic acid with
coenzyme A to produce the final product,
acetyl coenzyme A (acetyl CoA)
•
Acetyl CoA enters the Krebs Cycle
Krebs (Citric Acid) Cycle
• Coenzyme A shuttles the
2-carbon acetic acid to an
enzyme that condenses it
with a 4-carbon acid
called oxaloacetic acid to
produce the 6 carbon
citric acid
– Because citric acid is the
first substrate of the
cycle, biochemists prefer
to call the Krebs cycle
the citric acid cycle
Krebs (Citric Acid) Cycle
•
•
•
As the cycle moves through its
eight successive steps, the atoms
of citric acid are rearranged to
produce different intermediate
molecules, most called keto acids
At the end of the cycle, acetic acid has
been totally disposed of and
oxaloacetic acid, the pickup molecule,
is regenerated
Two decarboxylations and four
oxidations occur:
–
–
Products are 2CO2 molecules and 4
molecules of reduced coenzymes (3
NADH + H+ and 1
FADH2)(Nicotinamide adenine
dinucleotide and Flavin adenine
dinucleotide)
Notice that it is the Kreb cycle reactions
that produce the CO2 evolved during
glucose oxidation
Krebs (Citric Acid) Cycle
•
Glycolysis: oxygen not used
–
–
–
Two molecules of pyruvic acid
Two molecules of reduced NAD+
(NADH + H+)
Net gain of two ATP molecules per
glucose molecule
•
•
4 ATPs are produced, but remember
that 2 are consumed in phase 1
Krebs (Citric Acid) Cycle: oxygen
not used:
–
Two molecules of pyruvic acid enter
•
•
Six molecules of CO2
Ten molecules of reduced coenzymes
(removal of 10 hydrogen atoms)
–
–
•
•
8 NADH + H+
2 FADH2
Two ATP
Total at this point:
–
–
6CO2
4ATP
KREBS CYCLE
Krebs (Citric Acid) Cycle
• Although the glycolytic pathway is exclusive
to carbohydrate oxidation, breakdown
products of carbohydrate, fats, and proteins
can feed into the Krebs cycle to be oxidized
for energy
– Some Krebs cycle intermediates can be siphoned off
to make fatty acids and nonessential amino acids
• Thus the Krebs cycle, besides serving as the
final common pathway for the oxidation of
food fuels, is a source of building materials
for anabolic reactions
Electron Transport Chain and
Oxidative Phosphorylation
• Electron transport chain is the final catabolic
reactions that occur on the mitochondrial cristae
– Consumes oxygen
– However, because the reduced coenzymes produced in the
Krebs cycle are the substrates for the electron transport chain,
these pathways are coupled, and both phases are considered to
be oxygen requiring (aerobic)
• Hydrogens removed during the oxidation of foods
are combined with O2, and the energy released
during those reactions is harnessed to attach Pi
(inorganic phospahtes) groups to ADP
– Process called oxidative phosphorylation
Electron Transport Chain and
Oxidative Phosphorylation
•
Most components of the electron
transport chain are proteins that are
bound to metal (Fe, S) atoms (cofactors):
–
–
–
–
–
–
–
•
Part of the mitochondrial cristae
Cluster together to form major respiratory
enzyme complexes that are alternately
reduced and oxidized by picking up electrons
and passing them on to the next complex in
the sequence
The hydrogen atoms delivered to the electron
transport chain by the reduced coenzymes
are quickly split into protons (H+) plus
electrons
The electrons are shuttled along the crista
membrane from one acceptor to the next
The protons escape into the watery matrix
The electrons are delivered to an oxygen
atom creating oxygen (O-) ions
Strongly attract H+ (hydrogen ions) and
form water
Virtually all the water resulting from
glucose oxidation is formed during
oxidative phosphorylation
HYPOTHETICAL MECHANISM OF
OXIDATIVE PHOSPHORYLATION
ELECTRONIC ENERGY GRADIENT IN
THE ELECTRON TRANSPORT CHAIN
Electron Transport Chain and
Oxidative Phosphorylation
• Because NADH + H+ (Nicotinamide
adenine dinucleotide) and FADH2 (Flavin
adenine dinucleotide) are oxidized as they
release their burden of picked-up
hydrogen atoms, the net reaction for the
electron transport chain is:
• Coenzyme-2H + ½O2 → coenzyme + H2O
– reduced coenzyme
oxidized coenzyme
Electron Transport Chain and
Oxidative Phosphorylation
•
•
•
•
The transfer of electrons from
NADH + H+ to oxygen releases large
amounts of energy
If hydrogen combined directly with
molecular oxygen, the energy would
be released in one big burst and most
of it would be lost to the environment
as heat
Instead energy is released in many
small steps as the electrons stream
from one electron acceptor to the
next
Each successive carrier has a greater
affinity for electrons than those
preceding it
–
Therefore, the electrons cascade
downhill from NADH + H+ to
progressively lower energy levels until
they arte finally delivered to oxygen,
which has the greatest affinity of all for
electrons
Electron Transport Chain and
Oxidative Phosphorylation
• As the protons take
cascade they create
an electric current,
and ATP synthase
harnesses this
electrical energy to
catalyze attachment
of a Phosphate group
to ADP to form ATP
Electron Transport Chain and
Oxidative Phosphorylation
• Rotating structure of
ATP synthase (like
rotating water wheel)
activates catalytic
sites resulting in ADP
joining with inorganic
phosphate (Pi)
producing ATP
ATP SYNTHASE
HOMEOSTATIC IMBALANCE
• Metabolic poisons binds to enzymes
disrupting the metabolic pathways
Summary of ATP Production
•
Glycolysis: oxygen not used
–
–
–
Two molecules of pyruvic acid
Two molecules of reduced NAD+ (NADH + H+)
Net gain of two ATP molecules per glucose
molecule
•
•
4 ATPs are produced, but remember that 2 are
consumed in phase 1
Krebs (Citric Acid) Cycle: oxygen not used
–
Two molecules of pyruvic acid enter
•
•
Six molecules of CO2
Ten molecules of reduced coenzymes (removal
of 10 hydrogen atoms)
–
–
•
•
Two ATP
Total at this point:
–
–
•
8 NADH + H+
2 FADH2
6CO2
4ATP
Oxidative phosphorylation:
–
Every time NADH + H+ and FADH2 are
produced, ATPs are formed
CELLULAR RESPIRATION
Glycogenesis and Glycogenolysis
•
When more glucose is available than
can be immediately oxidized, rising
intracellular ATP concentrations
eventually inhibit glucose catabolism
and initiate processes that store
glucose as either glycogen or fat
–
•
Glycogenesis is the formation of
glycogen, the animal storage form of
glucose, that occurs when excess
glucose is ingested
–
•
Because the body can store much
more fat than glycogen, fats account for
80-85% of stored energy
Liver and skeletal muscle cells are
most active in glycogen synthesis and
storage
Glycogenolysis is the breakdown of
glycogen into individual glucose
molecules that occurs when the blood
sugar levels drop
GLYCOGENESIS
AND
GLYCOGENOLYSIS
Gluconeogenesis
• Gluconeogenesis is the process of forming
new glucose from noncarbohydrate
molecules that occurs in the liver using
glycerol and amino acids:
– It takes place when dietary sources and glucose
reserves have been depleted and blood glucose
levels are beginning to drop
– Protects the body, the nervous system on particular,
from the damaging effects of low blood sugar
(hypoglycemia) by ensuring that ATP synthesis can
continue
LIPID METABOLISM
• Fats are the body’s most concentrated source of
energy
• They contain little water, an the energy yield from fat
catabolism is approximately twice that from either
glucose or protein catabolism—9 kcal per gram of fat
versus 4 kcal per gram of carbohydrate or protein
• Most products of fat digestion are transported in lymph in
the form of fatty-protein droplets called chylomicrons
– Eventually, the lipids in the chylomicrons are hydrolyzed by
plasma enzymes, and the resulting fatty acids and glycerol are
taken up by body cells and processed in various ways
Oxidation of Glycerol and Fatty
Acids
•
•
Of the various lipids, only neutral fats are
routinely oxidized for energy
Neutral fats: consist of fatty acid chains and
glycerol; also called triglycerides or triacylglycerols
– Commonly known as oils when liquid
– Their catabolism involves the separate
oxidation of their two different building
blocks: glycerol and fatty acid chains
• Most body cells easily convert glycerol
to glyceraldehyde phosphate, a
glycolysis intermediate that enters the
Krebs cycle
• Beta oxidation: occurs in the
mitochondria
– Is the first phase of fatty acid
metabolism where fatty acid
chains are split into two carbon
acetic acid fragments and
coenzymes are reduced forming
acetyl CoA
» Which is picked up by
oxaloacetic acid and
enters the aerobic
pathways to be oxidized to
CO2 and H2O
– Beta refers to the fact that the 3rd
carbon is oxidized and the
cleavage is between the alpha
and beta carbons
INITIAL PHASE OF LIPID
OXIDATION
Lipolysis
•
Is the breakdown of stored fats into glycerol and fatty acids to be used
by the body for fuel:
– Released to the blood, helping to ensure that body organs have continuous
access to fat fuels for aerobic respiration
• The liver, cardiac muscle, and resting skeletal muscles actually prefer fatty acids as an
energy fuel
•
•
When carbohydrate intake is inadequate, lipolysis is accelerated as
the body attempts to fill the fuel gap with fats depending on the
availability of oxaloacetic acid to act as the pickup molecule to help
enter the Krebs Cycle
When carbohydrates are deficient, oxaloacetic acid is converted to
glucose (to fuel the brain)
– Without oxaloacetic acid, fat oxidation is incomplete resulting in ketones, which
are released into the blood
• When they accumulate in the blood, ketoacidosis can result
–
–
–
–
pH drops
Disrupts heart activity and oxygen transport
Severe depression of nervous system
Common consequence of starvation, unwise dieting ( inadequate amounts of carbohydrates),
and diabetes mellitus
– Coma and death
METABOLISM OF TRIGLYCERIDES
Lipogenesis
• Reversal of Lipolysis
• Is the reformation of triglycerides from unused
glycerol and fatty acid chains for storage in the body
– Glycerol and fatty acids not immediately needed for energy are
recombined into triglycerides and stored
• About 50% ends up in subcutaneous tissue; the balance is stored in
other fat areas of the body
• Occurs when cellular ATP and glucose (easily
converted to fat) levels are high
• Even if the diet is fat-poor, carbohydrate intake can
provide all the raw materials needed to form neutral fats
METABOLISM OF TRIGLYCERIDES
PROTEIN METABOLISM
• Proteins have a limited life span and
must be broken down and replaced
before they begin to deteriorate
– Newly ingested amino acids transported in the
blood are taken up by cells by active transport
processes and used to replace tissue proteins
• When more protein is ingested than is
needed for these anabolic purposes,
amino acids are oxidized for energy or
converted to fat
Oxidation of Amino Acids
• Before amino acids can
be oxidized for energy,
they must be
deaminated, that is,
their amine group (NH2)
must be removed:
– The resulting molecule is
then converted to pyruvic
acid or to one of the keto
acid intermediates in the
Krebs cycle
– The key molecule in these
conversions is the
nonessential amino acid
glutamic acid
Transamination
• Transamination is
the process of
transferring an amine
group to alphaketoglutaric acid (a
Krebs cycle keto acid)
to make glutamic acid
– The original amino
acid becomes a keto
acid (oxygen atom
where the amine
group formerly was)
Oxidative Deamination
• Occurs in the liver and
removes the amine group of
glutamic acid as ammonia
(NH3) and regenerates alphaketoglutaric acid:
– The NH3 (toxic to the body)
combines with CO2 yielding
urea and water
• The urea is released to the
blood and excreted in the
urine
• This mechanism rids the body
not only of NH3 produced
during oxidative deamination,
but also of bloodborne NH3
produced by intestinal
bacteria
Keto Acid Modification
• The goal of amino acid
degradation is to produce
molecules that can be either
oxidized in the Krebs cycle
or converted to glucose
• Keto acid modification is used
to produce molecules that can
be oxidized in the Krebs cycle
or converted to glucose from
keto acids produced through
transamination
– Most important of these
metabolites are pyruvic acid,
acetyl CoA, alpha-ketoglutaric
acid, and oxaloacetic acid
TRANSAMINATION
Protein Synthesis
•
Amino acids are the most important anabolic nutrients:
– Protein structures
– Enzymes
•
•
•
Occurs in the ribosomes, where cytoplasmic enzymes oversee the
formation of peptide bonds linking the amino acids together into protein
polymers
The amount and type of protein synthesized are precisely controlled
by hormones (growth, thyroxine, sex hormones, etc.)
You do not need to ingest extreme amounts of proteins because
nonessential amino acids are easily formed by removing keto acids from the
Krebs cycle and transferring amine groups to them
– Most of these transformations occur in the liver, which provides nearly all the
nonessential amino acids needed to produce the relatively small amount of
protein that the body synthesizes each day
– However, a complete set of amino acids must be present for protein synthesis to
take place, so all essential amino acids must be provided by the diet
• If some are not, the rest are oxidized for energy even though they may be needed for
anabolism
– Negative nitrogen balance results because body protein is broken down to supply the essential
amino acids needed
METABOLISM
• The body exists in a
dynamic catabolicanabolic state, where
substances are
continually being broken
down and rebuilt
• The body nutrient pools—
amino acids,
carbohydrates, and fat
stores—can be drawn on
to meet its varying needs
– These pools are
interconvertible because
their pathways are linked
by key intermediates
NUTRIENT POOL
METABOLISM
• The liver, adipose
tissue, and skeletal
muscles are the
primary effector
organs determining
the amounts and
direction of the
conversions
PATHWAYS OF INTERCONVERSION OF
CARBOHYDRATES, FATS, AND PROTEINS
Absorptive and Postabsorptive
States
• Absorptive state is the time during and shortly after
eating when nutrients are moving into the blood
from the GI tract:
– Anabolism exceeds catabolism
– Absorbed monosaccharides are delivered directly to the liver
where they are converted into glucose and either used by the
cells of the body, stored as glycogen, or converted into fats to be
stored
– Triglycerides are either used for anabolic purposes or stored in
adipose tissue
– Amino acids are delivered to the liver, which delaminates some
and uses others to make plasma proteins, but most remain in the
blood to be distributed to body cells
MAJOR EVENTS AND PRINCIPAL METABOLIC
PATHWAYS OF THE ABSORPTIVE STATE
Hormonal Control
• Insulin directs all
events of the
absorptive state
EFFECTS OF INSULIN ON
METABOLISM
Postabsorptive State
• Postabsorptive state is the period when the
GI tract is empty and energy resources are
supplied by the body reserves:
– Glycogenolysis: breaking down of glycogen
• Source of blood glucose include glycogen in the liver,
skeletal muscle cells, adipose tissues, and cellular proteins
– Lipolysis in adipose tissues and the liver
• Adipose tissue and liver cells produce glycerol by lipolysis,
and the liver converts the glycerol to glucose
– Catabolism of cellular protein:
• Cellular amino acids are deaminated and converted to
glucose in the liver
– During extended periods of fasting the kidneys are also capable
of gluconeogenesis
MAJOR EVENTS AND PRINCIPAL METABOLIC
PATHWAYS OF THE POSTABSORPTIVE STATE
Glucose Sparing
• Glucose sparing is the increased use of
noncarbohydrate fuel molecules (especially
triglycerides) for energy to conserve glucose
during times of fasting
• As the body progresses from absorptive to
postabsorptive state, the brain continues to
take its share of blood glucose; but virtually
every other organ switches to fatty acids as
its major energy source, thus sparing
glucose for the brain
Hormonal and Neural control
• The sympathetic
nervous system and
several hormones
interact to control the
postabsorptive state
INFLUENCE OF GLUCAGON ON PLASMA
GLUCOSE CONCENTRATION
LIPIDS
• Any one of a group of fats or fatlike substances, characterized
by their insolubility in water and solubility in fat solvents such
as alcohol, ether, and chloroform
• Term is descriptive rather than a chemical name such as protein or
carbohydrate
• Includes:
– True fats (esters of fatty acids and glycerol)
– Lipoids:
• Phospholipids: lipid with phosphorus (a diglyceride containing phosphorus)
• Cerebrosides: lipid in nerves
• Waxes:
– Sterols:
• Cholesterol: C27H45OH, a monohydric alcohol (having a single replaceable
hydrogen atom)
– Sterol widely distributed in animal tissues
• Ergosterol: fat in the cell membrane of fungi
– Role similar to that of cholesterol in human cells
Triglyceride (Fats)
Phospholipids
Phospholipids
Cholesterol
Steroids
Cholesterol
Sterol/Cholesterol
Cholesterol
Development of various Steroids
Cholesterol
Metabolic Role of the Liver
• The liver processes nearly every class
of nutrient and plays a major role in
regulating plasma cholesterol levels
• The hepatocytes carry out over 500
metabolic functions
Cholesterol Metabolism
• Cholesterol is not used as an energy source:
– Cholesterol serves as the structural basis for bile
salts, steroid hormones, vitamin D; as a component of
the plasma membrane; and as a signaling molecule in
embryonic development
– About 85% of cholesterol (15% in our diet) is made in
the liver from acetyl CoA and other body cells
(particularly intestinal cells), and is lost from the body
in bile salts in feces
Cholesterol Transport
• Triglycerides (neutral fats) and
cholesterol are insoluble in water and
must be transported in the body bound
to small lipid-protein complexes called
lipoproteins
• In general, the higher the percentage of
lipid in the lipoprotein, the lower its density
• The greater the proportion of protein, the
higher its density
Cholesterol Transport
• HDLs: high-density
lipoproteins (higher
protein)
• LDLs: low-density
lipoproteins (higher lipids)
• VLDLs: very low density
lipoproteins
• Chylomicrons: transport
absorbed lipids from the
GI tract, are a separate
class and have the lowest
density
APPROXIMATE COMPOSITION OF
LIPOPROTEINS THAT TRANSPORT LIPIDS IN
BODY FLUIDS
Cholesterol Transport
• VLDLs is primarily produced in the liver
– Transports triglycerides from the liver to the peripheral tissues,
but mostly to adipose tissues
– Triglycerides are unloaded, the VLDL residues are converted to
LDLs
• LDLs: are cholesterol rich
– Transports cholesterol to peripheral tissues, making it available
to the tissue cells for membrane or hormone synthesis and for
storage for later use
– Regulate cholesterol synthesis in the tissue cells
• HDL: rich in phospholipids
– Transport excess cholesterol from peripheral tissues to the liver,
where it is broken down and becomes part of bile
Cholesterol
Cholesterol Counts
• Total Cholesterol: above 200mg/100ml blood
– Linked to risk of atherosclerosis (clogs the arteries
and causes strokes and heart attacks)
– Not enough to simply measure total cholesterol
– The form in which cholesterol is transported in the
blood is more important clinically
• HDLs:
– High levels are considered good because the transported
cholesterol is destined for degradation
» 35-60: okay
» Above 60: protects against heart disease
• LDLs:
– High levels are considered bad because potentially lethal
deposits are laid down in the artery walls
Cholesterol Levels
Factors Regulating Plasma
Cholesterol Levels
• A negative feedback loop partially adjusts the
amount of cholesterol produced by the liver
according to cholesterol in the diet:
– Severe restriction of dietary cholesterol does not lead to a steep
reduction in plasma cholesterol levels since the liver produces a
certain amount of cholesterol even when dietary intake is
excessive (NO MJAOR NEGATIVE FEEDBACK MECHANISM)
• Saturated fatty acids stimulate liver synthesis of
cholesterol and inhibit its excretion from the body
– Thus, moderate decreases in intake of saturated fats (animal fats
and coconut oil) can reduce cholesterol levels
Factors Regulating Plasma
Cholesterol Levels
• In contrast, unsaturated fatty acids (most vegetable
oils) enhance excretion of cholesterol from the body and
its catabolism to bile salts, thereby reducing total
cholesterol levels
– Exception:
• Healthy oils that have been hardened by hydrogenation to make
them more solid
– Hydrogenation is a process of changing an unsaturated fat to a solid
saturated fat by the addition of hydrogen in the presence of a catalyst
• Hydrogenation changes the fatty acids in the oil to trans fatty acids
– Cause serum changes worse than those caused by saturated fats
» Trans fatty acids cause a greater increase in LDL levels and a
greater reduction in HDL levels than saturated fatty acids
(producing the unhealthiest ratio of total cholesterol to HDL)
Factors Regulating Plasma
Cholesterol Levels
• The unsaturated omega-3 fatty acids found in
certain fish lowers the proportions of both
saturated fats and cholesterol
• The omega-3 fatty acids (linoleic and
arachidonic) have a powerful antiarrhythmic
effect on the heart and also make blood
platelets less sticky, thus helping prevent
spontaneous clotting that can block blood
vessels
– Lowers blood pressure even in nonhypertensive
people
Omega-3
Omega-3/6
• It is very important to maintain a balance between
omega-3 and omega-6 fatty acids in the diet. Omega3 fatty acids help reduce inflammation and most
omega-6 fatty acids tend to promote inflammation.
An inappropriate balance of these essential fatty acids
contributes to the development of disease while a proper
balance helps maintain and even improve health. A
healthy diet should consist of roughly one to four times
more omega-6 fatty acids than omega-3 fatty acids. The
typical American diet tends to contain 11 to 30 times
more omega-6 fatty acids than omega-3 fatty acids and
many researchers believe this imbalance is a significant
factor in the rising rate of inflammatory disorders in the
United States.
Omega-3/6
• In contrast, however, the Mediterranean diet
consists of a healthier balance between omega3 and omega-6 fatty acids and many studies
have shown that people who follow this diet are
less likely to develop heart disease. The
Mediterranean diet does not include much meat
(which is high in omega-6 fatty acids) and
emphasizes foods rich in omega-3 fatty acids
including whole grains, fresh fruits and
vegetables, fish, olive oil, garlic, as well as
moderate wine consumption.
Omega-3
• Eat a variety of (preferably fatty) fish at
least twice a week. Include oils and foods
rich in alpha-linolenic acid (flaxseed,
canola and soybean oils; flaxseed and
walnuts).
Omega-3
• Oily fish (oil-rich fish, pelagic fish) are those fish which have oils
throughout the fillet and in the belly cavity around the gut, rather
than only in the liver like white fish. Oily fish fillets may contain up to
30 percent oil, although this figure varies both within and between
species. Oily fish generally swim in mid-waters or near the surface
(the pelagic zone).
• Oily fish are a good source of Vitamins A and D as well as being rich
in Omega 3 fatty acids. For this reason the consumption of oily fish
has been identified as more beneficial to humans than white fish.
Amongst other benefits, studies suggest that the Omega 3 fatty
acids in oily fish may help sufferers of depression, reduce the
likelihood of heart disease and improve inflammatory conditions
such as arthritis.
Omega-3/6
• The main sources of omega-6 fatty acids are
vegetable oils such as corn oil and soy oil that
contain a high proportion of linoleic acid. Omega-3
acids are found in flaxseed oil, walnut oil, and
marine plankton and fatty fish. The main component of
flaxseed and walnut oils is alpha-linolenic acid while the
predominant fatty acids found in fatty fish and fish oils
are eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA). The most beneficial and active of these fatty
acids are EPA and DHA. Alpha-linolenic acid can be
converted to EPA and DHA in the body, but the
conversion is quite inefficient especially in older people.
[1, 2]
Omega-3
Omega-3
Factors Regulating Plasma
Cholesterol Levels
• In those with moderate to high cholesterol
levels, replacing half of the lipid-and
cholesterol-rich animal proteins in the diet
with soy protein lowers cholesterol levels
• Smoking, coffee drinking, and stress
increase LDL levels
• Regular aerobic exercise appears to
reduce LDL levels and increase HDL
levels
Cholesterol Levels
•
Studies indicate:
– That cholesterol levels below 190
for males and 178 for females
may be equally devastating
because they may enhance the
risk of “bleeding” strokes and
death from cerebral hemorrhage
– Almost half of those who get heart
disease have normal cholesterol
levels
• Others with poor lipid levels
remain free of heart disease
•
Although most Americans
would probably benefit from
reducing their intake of
saturated fats and cholesterolrich foods, at least for now, the
moderate approach to
cholesterol control may be the
wisest
ENERGY BALANCE
• First Law of Thermodynamics: energy can be
neither created nor destroyed—only converted
from one form to another
• A dynamic exists within the body between
the energy intake and energy output
– Energy intake is the energy liberated during food
oxidation
– Energy output includes energy lost as heat, energy
used to do work, and energy that is stored as fat or
glycogen
ENERGY BALANCE
• Regulation of Food Intake:
– Hypothalamus: releases several peptides that
influence feeding behavior
•
•
•
•
Orexins: appetite enhancer
Neuropeptide Y: causes us to crave carbohydrates
Galanin: causes us to crave for fats
GLP-1 (glucagon-like peptide) and serotonin make us
feel full and satisfied
– When energy intake and energy output are balanced
weight remains stable; when not balanced weight is
either lost or gained
ENERGY BALANCE
•
Current theories of how feeding behavior and hunger are related focus on one
or more of five factors: All of these factors appear to operate through feedback
signals to the feeding centers of the brain
–
Neural signals from the digestive system
•
Vagus nerve fibers carry on a two-way connection between the gut and brain
–
–
Bloodborne signals related to body energy stores
•
–
Levels of glucose, amino acids, and fatty acids
Hormones:
•
Insulin; pancreas
–
Leptin released by fat cells:
•
Glucagon: pancreas
–
•
•
Influences the storage of fat
Increases blood glucose level
Epinephrine: adrenal gland
–
–
Response to stress
Triggers hunger
Cholecystokinin: intestinal hormone secreted during food digestion
–
–
Depresses hunger
More in elderly people
Body temperature
•
–
Decreases blood glucose level
•
–
–
Response to presence of carbohydrates and proteins
Increased body temperature may inhibit eating
Psychological factors
FEEDING BEHAVIOR AND
SATIETY CONTROLS
Metabolic Rate and Heat Production
•
The body’s rate of energy
output is called the metabolic
rate, which is the total heat
produced by all the chemical
reactions and mechanical work
of the body
– Measured by directly by a
calorimeter: heat liberated by the
body is absorbed by water
circulating around a chamber
• Rise in temperature is related to
heat produced by the body
– Measured indirectly by a
respirometer
• Measures oxygen consumption,
which is proportional to heat
production
• Each liter of oxygen used, the
body produces about 4.8 kcal of
heat
INDIRECT MEASUREMENT OF METABOLIC
RATE BY RESPIROMETRY
Metabolic Rate and Heat Production
•
The basal metabolic rate (BMR) reflects the energy the body needs to
perform only its most essential activities, such as breathing and
maintaining resting levels of organ function
– This measurement is NOT the lowest metabolic state of the body
• This situation occurs during sleep, when the skeletal muscles are completely relaxed
– Reported in kilocalories per square meter of body surface per hour (kcal/m2/h)
• You can approximate your BMR by multiplying weight in kilograms (2.2 pounds=1Kg) by
1 if you are male and 0.9 if you are female
– 70-Kg male (154 lbs) has a BMR of 70 kcal/h
•
Factors influencing BMR include body surface area, age, gender,
stress, and hormones:
– Critical factor is body surface area: This reflects the fact that as the ratio of body
surface area to body volume increases, heat loss to the environment increases
and the metabolic rate must be higher to replace the lost heat
• Hence, if two people weigh the same, the taller and thinner person will have the higher
BMR
– Younger: higher MBR
• Large amounts of energy for growth
Metabolic Rate and Heat Production
• Factors influencing BMR include body surface area,
age, gender, stress, and hormones
• Gender: higher in males
• Males: more muscle which is very active metabolically
• Females: more fat which is metabolically sluggish
– Stress: physical or emotional increases BMR
– Hormones:
• Norepinephrine and epinephrine (adrenal medulla) increase BMR
• Thyroxine: most important hormonal factor in determining BMR
– Direct affect on most body cells (except brain cells) is to increase O2
consumption, presumably by accelerating the use of ATP to operate the
sodium-potassium pump
– As ATP reserves decline, cellular respiration accelerates
» Thus, the more thyroxine produced, the higher BMR
Metabolic Rate and Heat Production
• The total metabolic rate (TMR) is the
rate of kilocalorie consumption needed
to fuel all ongoing activities both
involuntary and voluntary
Regulation of Body Temperature
•
•
•
•
Body temperature regulation represents
a balance between heat production and
heat loss:
– The body’s core (organs within the
skull, thoracic and abdominal cavities)
has the highest temperature and its
shell (the skin) has the lowest
temperature in most circumstances
Although all body tissues produce heat,
those most active metabolically produce the
greatest amounts
Body temperature is usually maintained
within the range 35.6-37.80C (96-1000F)
– 36.20C (98.60F) being the average
Most adults go into convulsions
when body temperature reaches
410C (1060F)
–
430C (1100F) appears to be the
absolute limit for life
HEAT BALANCE
Core and Shell Temperatures
• Different body regions have different resting
temperatures:
– Core: organs within the skull and the thoracic and
abdominal cavities
• Higher temperature
– Shell: essentially the skin
• Lower temperature in most circumstances
– Varies when body is regulating temperature
• Of the two body sites used routinely to
obtain body temperature clinically, the
rectum typically has a temperature about
0.40C (0.70F) higher than the mouth and is a
better indicator of core temperature
Mechanism of Heat Exchange
• Heat always flows down its concentration gradient
from a warmer region to a cooler region
– Radiation is the loss of heat in the form of infrared waves
(thermal energy)
• 50% of body heat is lost
– Conduction is the transfer of heat from a warmer object to a
cooler one when the two are in direct contact with each other
– Convection occurs when the warm air surrounding the body
expands and rises and is replaced by cooler air molecules
– Evaporation removes large amounts of body heat when water
absorbs heat before vaporizing
HEAT EXCHANGE
Role of the Hypothalamus
• The brain’s main integrating center for
thermoregulation, containing the heat-loss
center and the heat-promoting center
Heat-Promoting Mechanisms
•
Heat-promoting mechanisms are triggered when the external
temperature is low, or blood temperature falls and the heat-promoting
center is activated
– Vasoconstriction of cutaneous blood vessels:
• Blood is restricted to deep body areas and largely bypasses the skin
– Skin is separated from deeper organs by a layer of insulating subcutaneous (fatty) tissue
– If restriction is extended, skin cells deprived of oxygen and nutrients begin to die (frostbite in
cold weather)
– Increase in metabolic rate:
• Cold stimulates the release of norepinephrine which elevates the metabolic rate
– Shivering:
• Involuntary shuddering contractions of muscles
– Increases body temperature because muscle activity produces large amounts of heat
– Enhanced thyroxine release:
• Thyroid hormone increases metabolic rate
– Behavioral modifications:
• Clothing
• Drink warm liquids
• Increased physical activity
MECHANISMS OF BODY
TEMPERATURE REGULATION
Heat-Loss Mechanisms
• Protect the body from excessively high
temperatures
• Whenever core body temperature rises
above normal, the hypothalamus heatpromoting center is inhibited:
– At the same time, the heat-loss center is activated
and so triggers one or both of the following:
• Vasodilation of cutaneous blood vessels:
– allows the body to lose heat through radiation, conduction, and
convection
• Enhanced sweating:
– If the body is extremely overheated or if the environment is so
hot that heat cannot be lost by other means, evaporation
becomes necessary
MECHANISMS OF BODY
TEMPERATURE REGULATION
Heat Stroke/Heat Exhaustion
• Hyperthermia: elevated body temperature
– Heat Stroke:
• Normal heat loss processes become ineffective
• Heat-control mechanisms are suspended, creating a vicious positive
feedback cycle
• Increasing temperature increase the metabolic rate, which increases heat
production
• Organ damage becomes a distinct possibility, including brain damage
– Heat exhaustion:
• Often used to describe the heat-associated collapse of an individual during
or following vigorous physical activity
– Evidenced by elevated body temperature and mental confusion and/or fainting
• Due primarily to dehydration and consequent low blood pressure
• In contrast to heat stroke, heat-loss mechanisms are still functional
• Can rapidly progress to heat stroke if the body is not cooled and rehydrated
promptly
Fever
•
•
Fever is controlled hyperthermia, usually resulting from an infection
somewhere in the body
Whatever the cause, white blood cells, injured tissue cells, and
macrophages release cytokines called pyrogens (fire starters), which
act on the hypothalamus, causing release of prostaglandins
– The hypothalamus is reset to a higher-than-normal temperature, causing
heat-promoting mechanisms to kick in:
•
•
•
•
Vasoconstriction
Heat loss from body surfaces declines
Skin cools
Shivering begins to generate heat
– Temperature rises until it reaches the new setting, and then is maintained
at that setting until natural body defenses or antibiotics reverse the
disease process
– Temperature is reset to a lower (normal) level:
• Heat-loss mechanisms swing into action
• Sweating begins
• Skin becomes flushed and warm
DEVELOPMENTAL ASPECTS OF
NUTRITION AND METABOLISM
• Embryological
– Good nutrition is essential in utero for the
growth of fetal tissues and brain
– Inadequate calories during the first three
years of life, a time of brain growth, will lead
to mental deficits or learning disorders
– Proteins are needed for muscle and bone
growth, and calcium is required for strong
bones
DEVELOPMENTAL ASPECTS OF
NUTRITION AND METABOLISM
• Aging
– By middle age and old age non-insulindependent diabetes mellitus becomes a
problem, especially in the obese
– Metabolic rate declines as we age
– Muscle and bones deteriorate, and the
efficiency of the endocrine system decreases