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Protein
Chapter 3
and
Vitamins
Chapter 5
Protein
Chapter 3
Protein
• A component of every living cell
• Accounts for 20% of adult weight
• Immune to the controversy over optimal intake
Protein—(cont.)
• Amino acids
– Basic building blocks of protein
– Composed of carbon, hydrogen, oxygen, and nitrogen
atoms
– Twenty common amino acids
o Nine are considered essential in the diet because
the body cannot make them—indispensable; they
must be consumed through food.
o Eleven are considered nonessential in the diet
because they can be made by the body—
dispensable. However…
o Conditionally essential amino acids-situation arises when
insufficient substrate(s) levels for synthesis of nonessential amino acids and/or a problem with the metabolic
machinery to make non-essential amino acids occurs
Essential Amino Acids
• Histidine
• Isoleucine
• Methionine
• Phenylalanine
• Threonine
• Leucine
• Lysine
• Tryptophan
• Valine
Nonessential Amino Acids
• Alanine
• Glutamic acid
• Arginine
• Glutamine
• Asparagine
• Glycine
• Aspartic acid
• Cystine (cysteine)
• Proline
• Serine
• Tyrosine
Protein—(cont.)
• Protein structure
– Most contain several dozen to several
hundred amino acids.
– Shape (i.e. structure) determines
function.
Protein—(cont.)
• Functions of protein
– Major structural and functional component of
every living cell
– Body structure and framework
– Enzymes
– Other body secretions and fluids
– Acid–base balance
– Transport molecules
Protein—(cont.)
• Functions of protein—(cont.)
– Other compounds
– Some amino acids have specific functions
within the body.
– Fueling the body
Protein—(cont.)
• How the body handles protein
– Digestion
o Begins in the stomach
o Hydrochloric acid converts pepsinogen to the
active enzyme pepsin.
o Small intestine is the principal site of protein
digestion.
o Enzymes located on the surface of the cells
that line the small intestine complete the
digestion.
Protein—(cont.)
• How the body handles protein—(cont.)
– Absorption
o Amino acids, and sometimes a few dipeptides or
larger peptides, are absorbed through the mucosa
of the small intestine.
– Metabolism
o Liver acts as a clearinghouse.
 Retains amino acids to make liver cells,
nonessential amino acids, and plasma proteins
such as heparin, prothrombin, and albumin
 Regulates the release of amino acids into the
bloodstream
Protein—(cont.)
• How the body handles protein—(cont.)
– Metabolism—(cont.)
o Liver acts as a clearinghouse.—(cont.)
 Removes the nitrogen from amino acids
 Converts amino acids to fatty acids which
form triglycerides for storage in adipose
tissue
 Forms urea from the nitrogenous wastes of
protein
Protein—(cont.)
• Protein synthesis
– Complicated but efficient process that quickly
assembles amino acids into proteins the body
needs
– Part of what makes every individual unique is the
minute differences in body proteins.
– Important concepts
o Protein turnover, metabolic pool, and nitrogen
balance
Important Concepts
Protein turnover
Metabolic pool
• Continuous process
• Contains supply of
each amino acid
• Body proteins vary in
their rate of turnover.
• Consists of recycled
amino acids from body
proteins that have
broken down and also
amino acids from food
• In a constant state of
flux
Important Concepts—(cont.)
• Nitrogen balance
– Reflects the state of balance between protein
breakdown and protein synthesis
– Determined by comparing the amount of
nitrogen consumed (intake) with the amount
of nitrogen excreted (output)
– Healthy adults are in neutral nitrogen
balance.
Important Concepts—(cont.)
• Nitrogen balance—(cont.)
– Positive nitrogen balance: when protein
synthesis exceeds protein breakdown
(e.g. growth, pregnancy)
– Negative nitrogen balance: an undesirable
state that occurs when protein breakdown
exceeds protein synthesis (e.g. illness,
insufficient dietary protein)
Protein—(cont.)
• Protein catabolism for energy
– Counterproductive-proteins (enzymes)
are required to get energy from
carbohydrates and lipids
– Over time, loss of lean body tissue
occurs.
– Loss of 30% of body protein causes
o Impaired breathing
o Altered immune function
o Altered organ function
o Ultimately death
Sources of Protein
• Protein quality
– Differs based on content of essential
amino acids and digestibility of the
protein
– Quality can become a crucial
concern.
Sources of Protein—(cont.)
• Complete and incomplete proteins
– Complete proteins
o High biologic value
o Provide adequate amounts and proportions of
all essential amino acids needed for protein
synthesis necessary to support tissue growth
and repair
o Animal proteins, soy, quinoa protein are
complete proteins- but with quinoa have
digestibility of protein issue- explain
Sources of Protein—(cont.)
• Complete and incomplete proteins—(cont.)
– Incomplete proteins
o Lack adequate amounts of one or more essential
amino acids
o Except for soy and quinoa protein, all plants are
sources of incomplete proteins.
o Gelatin is also an incomplete protein.
– Complementary proteins
o Two proteins that when combined provide
adequate amounts and proportions of all essential
amino acids needed to support protein synthesis
Examples of Complementary Plant Proteins
• Black beans and rice
• Bean tacos
• Pea soup with toast
• Lentil and rice curry
• Falafel sandwich (ground chickpeas on pita)
• Peanut butter sandwich
• Pasta e fagioli (pasta with white beans)
Examples of a Plant Protein
Complemented by a Small Amount of an
Animal Protein to Form a Complete
Protein
• Bread pudding
• Cheese fondue
• Rice pudding
• French toast
• Corn pudding
• Cheese sandwich
• Cereal and milk
• Macaroni and cheese
• Vegetable quiche
Dietary Reference Intakes
• RDAs
– For healthy adults is 0.8 g/kg
– Acceptable Macronutrient Distribution Range
for protein for adults is 10% to 35% of total
calories.
• RDA for healthy adults does not apply to
others than healthy adults
Dietary Reference Intakes—(cont.)
• Protein deficiency
– Protein–energy malnutrition (PEM)
o Kwashiorkor
 Results mainly from acute critical illnesses
 Enough energy but not enough protein
 Get swollen abdomen
 Aggressive nutritional support is used to
restore metabolic balance as quickly as
possible.
o Marasmus
 Occurs secondary to chronic diseases
 Not enough energy or protein
 Skin and bones appearance
 Nutritional therapy is started slowly and
advanced gradually.
Dietary Reference Intakes—(cont.)
• Protein excess
– No proven risks from eating an excess of
protein
– Conflicting data as to whether high-protein
diets increase the risk of:
o Osteoporosis
o Renal stones
o Renal disease
Protein in Health Promotion
• Vegetarian diets
– Pure vegetarians or vegans
o Eat no animal products.
o Eat only plants.
o They form the smallest group of vegetarians
o Must eat a wide variety of plant foods to get
sufficient of all essential amino acids
o Vitamin B12 usually comes from plant foods
with vitamin B12 added to food prior to
purchase or if that fails via vitamin B12 in
tablet form.
Protein in Health Promotion—(cont.)
• Vegetarian diets—(cont.)
– Most vegetarians are
o Lacto-vegetarians, whose diets include milk products
o Lacto-ovo vegetarians, whose diets include milk
products and eggs
• Nutrients of concern
– Most vegetarian diets meet or exceed the RDA for
protein and are nutritionally adequate across the life
cycle.
– Iron, zinc, calcium, vitamin D, omega-3 fatty acid, and
iodine are nutrients of concern.
Protein in Health Promotion—(cont.)
• Is vegetarianism for everyone?
– A personal choice, subject to personal
interpretation
– Proper planning means paying close
attention to the nutrients of concern and
using a vegetarian food guide for planning.
Vitamins
Chapter 5
Vitamins
• In 1913, thiamin was discovered as the first
vitamin, the “vital amine” necessary to prevent
the deficiency disease beriberi.
• Today, 13 vitamins have been identified as
important for human nutrition.
Understanding Vitamins
• Organic compounds made of carbon, hydrogen, oxygen, and
sometimes nitrogen or other elements
• Some vitamins facilitate biochemical reactions within cells
• Essential to life
• Individual molecules
• Do not provide energy (calories), but some are needed for
metabolism of energy
• Needed in microgram or milligram quantities
• Too little of a food source(s) of a vitamin leads to deficiencies
of that vitamin lead to loss of function (role) of vitamins
• Too much of a food source(s) or supplement of a vitamin
leads to toxicities lead to impairment of some bodily
functions-fat soluble vitamins are particularly a problem here
but some water soluble vitamins can also be affected
• A complete listing of the effects of various vitamin
deficiencies and toxicities is available online
Understanding Vitamins—(cont.)
• Vitamins may exist in more than one form
– Different forms perform different functions in
the body.
– Provitamins
• Vitamins are essential
– With few exceptions, the human body cannot
make vitamins. Humans can for example
make vitamin D
• Some vitamins are coenzymes
– Many enzymes cannot function without a
coenzyme, and many coenzymes are vitamins.
Understanding Vitamins—(cont.)
• Some vitamins are antioxidants
– Free radicals are produced continuously in cells
as they burn oxygen during normal metabolism.
o Oxidize body cells and DNA in their quest to
gain an electron and become stable
– Antioxidants protect body cells from being
oxidized (destroyed) by free radicals.
– Major antioxidants are vitamin C, vitamin E, and
beta-carotene.
Understanding Vitamins—(cont.)
• Some vitamins are used as food additives
– Some foods have vitamins added to them
simply to boost their nutritional content.
• Vitamins as drugs
– In megadoses, vitamins function like drugs,
not nutrients. e.g. vitamin E can lower ability
to clot
Vitamin Classifications Based on Solubility
• Fat-soluble vitamins
– Characteristics
o Sources are the fat and oil portion of foods.
o Absorption: fat encased in chylomicrons that enter
the lymphatic system before circulating in the
bloodstream
o Transportation through the blood occurs by
attaching to protein carriers because fat is not
soluble in watery blood.
o When consumed in excess, stored primarily in liver
and adipose tissue
Vitamin Classifications Based on
Solubility—(cont.)
• Fat-soluble vitamins
– Characteristics—(cont.)
o Can be toxic if consuming high intakes
through supplements –why?
o Generally do not have to be consumed
daily because the body can retrieve them
from storage as needed
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamins A,D,E,K are fat soluble
• B vitamins, non-B vitamins and vitamin C are
water soluble.
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin A
– Preformed vitamin A is found only in animal
sources.
– Also includes provitamin A carotenoids
o Natural plant pigments found in deep yellow
and orange fruits and vegetables and most
dark-green leafy vegetables
o Beta-carotene, lutein, and lycopene are among
the most commonly known carotenoids.
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin A—(cont.)
– Best known for its roles in normal vision,
reproduction, growth, and immune system
functioning
– Body can store up to a year’s supply of vitamin A.
– Only preformed vitamin A is toxic in high doses.
– Beta carotene is nontoxic.
– Hypercarotenemia –orange-coloured skin in
Caucasians
Vitamin Classifications Based On
Solubility—(cont.)
• Vitamin D
– Unique in that the body has the potential to make
all of the vitamin D it needs if exposure to
sunlight is optimal and liver and kidney function
are normal
– Another distinctive feature of vitamin D is that it
acts like a hormone because it is synthesized in
one part of the body (skin) and stimulates
functional activity elsewhere.
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin D—(cont.)
– Primary function of vitamin D is to maintain
normal blood concentrations of calcium and
phosphorus.
– Calcium and phosphorous are used for bone and
teeth development and maintenance
– Vitamin D is important for immune function.
– It is possible to fulfill the vitamin D requirement
by taking a daily 15-minute walk in the sun
under optimal conditions.
– Winter, living in northern latitudes, and being of
black race and older age are associated with low
vitamin D synthesis.
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin D—(cont.)
– Dietary source is considered essential because few
people meet optimal conditions.
o Vitamin D occurs naturally in only a few foods.
– Many experts believe the AI for vitamin D is set too
low.
– Overt deficiency of vitamin D causes poor calcium
absorption.
o Rickets and osteomalacia
– Current upper limit for vitamin D is set at 100
µg/day (4000 IU/day) for ages 9 years and older.
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin E
– Generic term that describes a group of at least
eight naturally occurring compounds
– Alpha-tocopherol is considered the most
biologically active form of vitamin E.
– Functions as the primary fat-soluble antioxidant
in the body
– Protects polyunsaturated fatty acids (PUFAs) and
other lipid molecules, such as LDL cholesterol,
from oxidative damage
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin E—(cont.)
– Need increases as the intake of PUFA increases.
– Megadoses may help protect against atherosclerosis,
some types of cancer, cataracts, age-related macular
degeneration, Parkinson’s disease, and Alzheimer’s
disease.
– Deficiency can occur in very specific instances.
o Premature infants
o May occur secondary to a genetic abnormality or
malabsorption syndromes such as cystic fibrosis
and short bowel syndrome
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin E—(cont.)
– Signs and symptoms of deficiency include
peripheral neuropathy, ataxia, and ultimately
death.
• Vitamin K
– Occurs naturally in two forms
o Phylloquinone, found in plants
o Menaquinones, which are synthesized in the
intestinal tract by bacteria
Vitamin Classifications Based on
Solubility—(cont.)
• Vitamin K—(cont.)
– Coenzyme essential for the synthesis of prothrombin
– Clinically significant vitamin K deficiency is defined as
vitamin K–responsive hypoprothrombinemia.
o Characterized by an increase in prothrombin time
– Deficiency does not occur from inadequate intake but
may occur secondary to malabsorption syndromes or
the use of certain medications that interfere with
vitamin K metabolism or synthesis, such as
anticoagulants and antibiotics.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins
– Thiamin
o Coenzyme in the metabolism of carbohydrates
and branched-chain amino acids
o Deficiency
Beriberi (what is beriberi?)
o Beriberi has been virtually eliminated.
o Deficiency is usually seen only in alcoholics.
o No adverse effects have been noted from high
intakes of thiamin.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Riboflavin
o Vitamin B2 is an integral component of the
coenzymes flavin adenine dinucleotide (FAD)
and flavin mononucleotide (FMN) that function
to release energy from nutrients in all body
cells.
o Milk and dairy products contribute the most
riboflavin to the diet.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Riboflavin—(cont.)
o Biochemical signs of inadequate riboflavin status
can appear after only a few days of poor intake.
o Elderly and adolescents are at greatest risk for
riboflavin deficiency.
o Deficiency symptoms include sore throat, cheilosis,
stomatitis, glossitis, and dermatitis.
o Certain diseases, such as cancer, heart disease,
and diabetes, precipitate or exacerbate riboflavin
deficiency.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Niacin
o Vitamin B3 exists as nicotinic acid and nicotinamide.
o Body can make it from the amino acid tryptophan.
o Niacin requirements are stated in niacin equivalents
(NEs).
o Part of the coenzymes nicotinamide adenine
dinucleotide (NAD) and nicotinamide adenine
dinucleotide phosphate (NADP), which are involved
in energy transfer reactions in the metabolism of
glucose, fat, and alcohol in all body cells
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Niacin—(cont.)
o Pellagra, the disorder caused by severe niacin
deficiency, is rare in the United States and usually
is seen only in alcoholics.
o Niacin deficiency may be treated with niacin,
tryptophan, or both.
o Large doses of niacin in the form of nicotinic acid
(1–6 g/day) are used therapeutically to lower total
cholesterol and LDL cholesterol and raise highdensity lipoprotein (HDL) cholesterol.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin B6
o Vitamin B6 and pyridoxine are group names
for six related compounds that include
pyridoxine, pyridoxal, and pyridoxamine.
o Plays a role in the synthesis, catabolism, and
transport of amino acids and in the conversion
of tryptophan to niacin
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin B6—(cont.)
o Deficiencies of vitamin B6, folic acid, and
vitamin B12 lead to an increase in blood
homocysteine levels.
o Supplements of vitamin B6 have been used for
a variety of other conditions, although
supportive evidence is lacking.
o High intake of vitamin B6 from food does not
pose any danger.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin B6—(cont.)
o Deficiencies of vitamin B6 are uncommon but
are usually accompanied by deficiencies of
other B vitamins.
o Secondary deficiencies are related to alcohol
abuse and to other drug therapies such as
isoniazid, the antituberculosis drug that acts
as a vitamin B6 antagonist.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Folate
o Generic term for this B vitamin that
includes both synthetic folic acid found in
vitamin supplements and fortified foods
and naturally occurring folate in food such
as green leafy vegetables, dried peas and
beans, seeds, liver, and orange juice
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Folate—(cont.)
o Major function is in the synthesis of DNA.
o Folate is recycled through the intestinal tract.
o Folate deficiency impairs DNA synthesis and
cell division and results in macrocytic anemia
and other clinical symptoms.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Folate—(cont.)
o Adequate intake of folate before conception
and during the first trimester of pregnancy
reduces the risk of neural tube defects.
o Upper limit for folic acid is 1000 µg/day.
o Consistently high intakes of folate can mask
vitamin B12 deficiency.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin B12
o Cobalamin
o Vitamin B12 has important role in maintaining
the myelin sheath around nerves.
o Large doses of folic acid can alleviate the
anemia caused by vitamin B12 deficiency (a
function of both vitamins), but folic acid
cannot halt the progressive neurologic
impairments that only vitamin B12 can treat.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin B12—(cont.)
o Only water-soluble vitamin that does not
occur naturally in plants
o Requires an intrinsic factor
o Deficiency symptoms may take 5 to 10 years
or longer to develop.
o People with pernicious anemia require
parenteral injections of vitamin B12.
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin B12—(cont.)
o Recommended that people older than 50
years obtain most of their requirement from
fortified foods or supplements
– Other B vitamins
o Pantothenic acid
o Biotin
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Non–B vitamins
o Inositol
o Choline
o Carnitine
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin C
o Ascorbic acid
o Found in citrus fruits and juices
o Prevents scurvy
o Water-soluble antioxidant that protects
vitamin A, vitamin E, and PUFA from
destruction
Vitamin Classifications Based on
Solubility—(cont.)
• Water-soluble vitamins—(cont.)
– Vitamin C—(cont.)
o No clear and convincing evidence that large doses
of vitamin C prevent colds.
Vitamins in Health Promotion—(cont.)
• What about supplements?
– People who choose to take an all-purpose
multivitamin should select one that provides
100% of the daily value (DV) for vitamins with
an established DV.
– The USP stamp ensures the quality of
supplements but not the safety or benefits.
– High-cost supplements are not necessarily
superior to lower cost ones.
Vitamins in Health Promotion—(cont.)
• Can supplements be used as insurance against
poor food choices?
– Supplements are not substitutes for healthy
food: “supplement” means “add to,” not
“replace.”
– Supplements indicated only when diet cannot
provide enough vitamin or there is a digestion,
absorption or metabolism not allowing WWFQ for
a particular vitamin(s)
• A word of caution
– Supplements taken to augment a dietary intake
that is already adequate are unnecessary and
expensive with no benefit