Download Chapter 6 – The Proteins and Amino Acids

Chapter 6 – The Proteins and Amino Acids
●Proteins
-Compounds composed of carbon, hydrogen, and nitrogen and arranged as strands of amino acids
-Some amino acids also contain the element sulfur
-Versatile and vital cellular working molecules
●Some are working molecules
-Enzymes
-Hormones
-Antibodies
-Cellular “pumps”
-Transport vehicles
-Oxygen carriers
-Etc.
●Some are structural molecules
-Tendons
-Ligaments
-Scars
-Fibers of muscles
-Cores of bone and teeth
-Filaments of hair
-Materials of nails
-Etc.
The Structure of Proteins
●Unlike carbohydrates and fats, proteins contain nitrogen
-Hence the name amino
-Are composed of amino acids
-The amino acids in a strand of protein are different from one another
-About 20 amino acids make up most of the proteins of living tissue
Amino Acids
●The building blocks of protein
●Each has an amine group at one end
-The nitrogen-containing part
●An acid group at the other end
●A distinctive side chain attached to the carbon at the center of the backbone
-Gives identity and chemical nature to each amino acid
●Side chains
-Make the amino acids differ in
-Size
-Shape
-Electrical charge
-Some negative, some positive, some with no charge
-Long strands of amino acids form large protein molecules
-The side chains of the amino acids ultimately help to determine the molecules’
shapes and behaviors
●Essential amino acids
-Amino acids that either cannot be synthesized at all by the body or cannot be
synthesized in amounts sufficient to meet physiological needs
-The body can make other amino acids from fragments derived from
carbohydrates or fat to form the backbones and nitrogen from other sources to
form the amine group
-Also called indispensable amino acids
-Without these essential nutrients, the body cannot make the proteins it needs to do its work
-Can only be replenished from foods
-Thus, a person must frequently eat the foods that provide them
-Histidine
-Isoleucine
-Leucine
-Lysine
-Methionine
-Phenylalanine
-Threonine
-Tryptophan
-Valine
●Conditionally essential amino acid
-An amino acid that is normally nonessential
-Under special circumstances, when the need for it exceeds the body’s ability to produce
it, it must be supplied by the diet
●Example of a conditionally essential amino acid:
-The body normally makes tyrosine (normally a nonessential amino acid) from
phenylalanine (an essential amino acid)
-If the diet fails to supply enough phenylalanine, or if the body cannot make the
conversion (as in the case of phenylketonuria), then tyrosine becomes a conditionally
essential amino acid
●Recycling Amino Acids
-In addition to making some amino acids the body breaks down proteins and reuses those
amino acids
-Food proteins and body proteins are dismantled to liberate their component
amino acids
-Providing the body with the raw materials from which it can build the
protein molecules it needs
●Cells can use amino acids for energy
-Discarding the nitrogen atoms as waste
-However, by reusing amino acids to build proteins the body conserves a valuable
commodity while easing its nitrogen disposal burden
-Provides access to an emergency fund of amino acids in times of fuel, glucose, or
protein deprivation
-At such times, tissues can break down their own proteins, sacrificing working
molecules to supply energy and amino acids to the body’s cells
●The body employs a priority system in selecting the tissue proteins to dismantle
-The most dispensable ones are used first
-such as the small proteins of the blood and muscle
-Structural proteins of certain organs are guarded until their use is forced by dire need
-such as structural protein of the heart and other organs
How Do Amino Acids Build Proteins?
●Peptide bond
-Connects one amino acid to another
-Formed between the amine of one amino acid and the acid group of the next amino acid
-Forms a straight chain of amino acids with side chains bristling out from the backbone
●Strand of protein does not remain a straight chain
-Amino acids at different places along the strand are chemically attracted to one another
-causes some segments of the strand to coil
-each spot along the coil is attracted to, or repelled from, other spots along its
length
-result of these interactions is to cause the entire chain to form either a globular
structure or a fibrous chain
●Amino acids whose side chains are electrically charged are attracted to water
-Thus, in the body’s watery fluids they orient themselves on the outside of the protein
structure
●Amino acids whose side chains are neutral are repelled by water
-Thus, in the body’s watery fluids they tuck themselves into the center, away from the
body’s fluids
●All of the interactions among the amino acids and the surrounding fluids give each
protein a unique architecture
-A form that is suited to its function
●Some proteins are composed of more than a single amino acid chain
●A metal ion (mineral) or a vitamin may need to join a protein in order to activate the
protein
The Variety of Proteins
●The particular shapes of proteins enable them to perform different tasks in the body
-Globular proteins are water soluble
-such as some proteins of the blood
-Some proteins form hollow balls
-can carry and store materials in their interior
●Some proteins are more than 10x as long as they are wide
-forming stiff, rodlike structures
-insoluble in water and very strong
-such as the proteins of tendons
●Collagen
-A protein from which connective tissues are made
-scars, tendons, ligaments, and the foundations of bones and teeth
-Acts somewhat like glue between cells
●Insulin
-Helps regulate blood sugar
●Enzymes
-Protein catalysts
-A catalyst is a substance that facilitates a chemical reaction without itself being
altered in the process
●Some protein strands function alone
●Other proteins are composed of several strands
-Hemoglobin
-Large, globular protein
-Packed into red blood cells
-Carries oxygen
-Made of 4 associated protein strands
-Each strand holding an iron atom
●A great variety of proteins is possible because an essentially infinite number of
sequences of the 20 different amino acids can be found
-A single human cell may contain as many as 10,000 different proteins
-Each one present in thousands of copies
●Inherited Amino Acid Sequences
-For each protein there exists a standard amino acid sequence
-A sequence which is specified by heredity
-If a wrong amino acid is inserted, the result can be disastrous to health
-You are unique among human beings because of minute differences in your body
proteins
-These differences are determined by the amino acid sequences of your proteins
-Which are written into to genetic code you inherited from your parents
-You unique combination of genes directs the making of all your body’s proteins
-Ultimately, the genes determine the sequence of amino acids in each finished protein
-Some genes are involved in making more than one protein
-As scientists completed the human genome they recognized that a greater task still lay
ahead
-The identification of every protein made by the human body
●Sickle-cell disease
-An example of an inherited variation in amino acid sequence
-Hemoglobin, the oxygen-carrying protein of red blood cells, is abnormal
-Normal hemoglobin contains two kinds of protein strands
-In sickle-cell disease, on one of the two kinds of strands, the 6th amino acid is
valine rather than glutamic acid
-This alters the protein so that it is unable to carry oxygen
-Red blood cells collapse from the normal disk shape into crescent shapes
-If too many of these types of red blood cells appear in the blood the results are
-Abnormal blood clotting
-Strokes
-Bouts of severe pain
-Susceptibility to infection
-Early death
●Genetic Expression and the Nutrients
-The making of a protein is referred to as “gene expression”
-Every human cell nucleus contains the DNA for making every human protein
-Cells do not make every protein
-Cells specialize in making certain proteins typical of their cell types
●Nutrients influence genetic expression
-And thus influence the resulting protein synthesis
●In general, cells moniter nutrient concentrations in the fluids surrounding them
-A nutrient lack or overabundance triggers a cascade of molecular events inside the cell
-Ultimately leads to expression or suppression of certain genes
●Examples
-Pancreas
-Responds to internal molecular messages generated when blood glucose is
overabundant by synthesizing insulin
-Results in a lowering of blood glucose concentration
-Hemoglobin
-When a body’s iron stores run low, immature red blood cells respond by
reducing hemoglobin synthesis
-In contrast, abundant iron stimulates hemoglobin synthesis by immature red
blood cells
●Denaturation of Proteins
-Denaturation
-The irreversible change in a protein’s shape
-Brought about by
-Heat
-Acids
-Bases
-Salts of heavy metals
-Alcohols
-Etc.
-The first step in the destruction of a protein
●Denaturation damages body proteins
●Denaturation is important to the digestion of food protein
-Stomach acids open up a protein’s structure
-Allows digestive enzymes to make contact with the peptide bonds and cleave
them
●Many well-known poisons are salts of heavy metals, such as mercury and silver
-These denature proteins whenever they touch them
-Common first-aid antidote for swallowing a heavy-metal poison is to drink milk
-The poison acts on the protein in the milk rather than on body protein
-Vomiting can later expel the milk-poison combination
Think Fitness: Can Eating Extra Protein Make Muscles Grow Larger?
●No
-Hard work, not excess dietary protein, is the trigger for the genes to build more muscle
tissue
-Exercise generates cellular messages that stimulate DNA to begin the process of
building up muscle fibers
-A snack rich in both protein and carbohydrate eaten directly after exercise may
help in this regard
Digestion and Absorption of Protein
●Each protein performs a particular task in a specific type of tissue of specific type of
organism
-When consuming a protein source the body must first alter the proteins by breaking them
down into amino acids
-These amino acids can then be arranged into specific human body proteins
●Digestion
-Proteins (enzymes), activated by acids, digest proteins from food, denatured by acid
-The coating of mucus secreted by the stomach wall protects its proteins from
attack by either acids of enzymes
-The normal acid of the stomach is so strong (pH 1.5) that no food is acidic
enough to make it stronger
Protein Digestion
●Mouth
-Protein is crushed by chewing and moistened with saliva
-Nothing happens to the protein until the strong acid of the stomach denatures it
●Stomach
-Acid helps to uncoil the protein’s tangled strands so that molecules of the stomach’s
protein-digesting enzyme can attack the peptide bonds
-The stomach’s protein-digesting enzyme works best in an acidic environment
-stomach lining is protected from acid and enzymes by a mucus coating secreted by
stomach cells
●Small Intestine
-Receives small denatured pieces of protein from the stomach
-A few are single amino acids
-Most are polypeptides
-Protein fragments of 10+ amino acids bonded together
-> a strand of 4-10 amino acids is called an oligopeptide
-Alkaline juices from the pancreas neutralize the acid delivered by the stomach
-The pH increases to about 7 (neutral)
-Protein-digesting enzymes from the pancreas and small intestine continue breaking
down protein until nearly all that is left are dipeptides, tripeptides, or single amino acids
●Failure to understand the mechanism of protein digestion can lead to being mislead by
advertisers urging, for example
-“Take enzyme A to help digest your food”.
-“Don’t eat food containing enzyme C, which will digest cells in your body.”
●Even the stomach’s digestive enzymes are denatured and absorbed when their jobs are
through
●Another false claim
-Predigested proteins (amino acid supplements) are “easy to digest” and can therefore
protect the digestive system from “overworking”
-The healthy digestive system handles whole proteins better than predigested ones
After Protein is Digested, What Happens to Amino Acids?
●Cells along the small intestine absorb single amino acids
-Cells that line that small intestine have enzymes on their surfaces that split most tri- and
dipeptides into single amino acids
-Which are then absorbed
●Some di- and tripeptides are absorbed into cells
-Where they are split into single amino acids before being released into the bloodstream
●A few larger peptide molecules can escape the digestive process altogether
-Enter the bloodstream intact
-It is thought that such peptides may act as hormones to regulate body functions
and provide the body with information about the external environment
-May also stimulate an immune response and thus play a role in food allergy
●Cells of the small intestine
-Posses separate sites for absorbing different types of amino acids
-Amino acids of the same type compete for the same absorption sites
-Thus, when a large dose of any single amino acid is ingested the absoption of
other amino acids of the same general type may be limited
The Roles of Proteins in the Body
●Proteins are versatile, unique and important to the body
Supporting Growth and Maintenance
●Amino acids must be continuously available to build the proteins of new tissue
-Embryo
-Muscles of an athlete in training
-Growing child
-New blood to replace losses
-Scar tissue
-New hair and nails
●Protein helps replace worn-out cells and internal cells structures
-Red blood cells live only 3-4 months
-Cells lining the intestinal tract live only 3 days
-Skin cells are constantly being shed and replaced
●Protein Turnover
-The continuous breakdown and synthesis of body proteins involving the recycling of
amino acids
-Each day about 25% of available amino acids are irretrievably diverted to other uses
-Such as being used for fuel
●Amino acids from food are needed each day to support all the new growth and
maintenance of cells and to make the working parts within them
Building Enzymes, Hormones, and Other Compounds
●Enzymes are among the most important of the proteins formed in living cells
-Thousands of enzymes reside inside a single cell
-Each a catalyst that facilitates a specific chemical reaction
●Hormones
-Chemical messengers secreted by a number of body organs in response to conditions
that require regulation
-Each hormone affects a specific organ or tissue and elicits a specific response
-Some are made from amino acids
-Some are made from lipids
●In addition to being building blocks for proteins, amino acids also perform other tasks
-Example: Tyrosine is a component of both epinephrine and norepinephrine and is used
to make both melanin and thyroxine
-Tryptophan serves as a starting material for serotonin and niacin
Building Antibodies
●Antibodies
-Large proteins of the blood
-Produced by the immune system
-Distinguish between “foreign” and “self” proteins
-Inactivate foreign proteins
-Each designed to destroy one specific invader
-Once the body has learned to make a particular antibody, it remembers
-The next time the body encounters the same invader, it destroys the invader even
more rapidly
-I.e. the body develops immunity to the invader
-The molecular memory underlies the principle of immunization
-Some immunities are lifelong
-Some must be “boosted” at intervals
Maintaining Fluid and Electrolyte Balance
●Too much fluid in a cell  the cell ruptures
●Too little fluid in a cell  the cell is unable to function
●Water can diffuse freely into and out of cells
●Proteins cannot
●Proteins attract water
-By maintaining stores of internal proteins, and some of minerals, cells retain the fluid
they need
●Fluid is kept within blood vessels by proteins that are too large to freely move across
capillary walls
-The proteins attract and hold water within the vessels
-Preventing the water from freely flowing into the spaces between cells
●Failure or any part of the fluid balance system  edema
-The swelling of body tissue caused by the leakage of fluid from the blood vessels
-Seen in protein deficiency, and other conditions
●The composition of body fluids is vital to life
-Transport proteins maintain this composition by continuously transferring substances
into and out of cells
Maintaining Acid-Base Balance
●Normal process of the body continually produce
-Acids
-compounds that release hydrogens in a water solution
-Bases
-compounds that accept hydrogens from solutions
●Acids and bases must be carried by the blood to the organs of excretion
-The blood must do this without allowing it own acid-base balance to be affected
-Blood proteins act as buffers to maintain the blood’s normal pH
-The protein buffers pick up hydrogens when there are too many in the
bloodstream
-The protein buffers release hydrogens when there are too few in the bloodstream
●Acidosis
-The condition of excess acid in the blood
-Indicated by a below-normal pH
●Alkalosis
-The condition of excess base in the blood
-Indicated by a above-normal pH
●Both acidosis and alkalosis can cause coma or death due to their effect on proteins
-Proteins can be denatured
-Disrupting many body processes
Providing Energy and Glucose
●If necessary, proteins will be surrendered to provide energy
-For most people eating a normal mixed diet, protein provides about 15% of the daily
need for energy
-Under conditions of inadequate energy or carbohydrate, protein use speeds up
-Obtaining energy is a top priority of the body
●Degradation of amino acids for energy
-Amine groups are stripped off
-used elsewhere
-Incorporated by the liver into urea and sent to the kidneys for excretion in the
urine
-Urea is the principal nitrogen-excretion product of protein metabolism
-Fragments that remain are composed of carbon, hydrogen, and oxygen
-As are carbohydrate and fat
-Can be used to build these nutrients
-Can be metabolized like these nutrients
●Unlike fatty acids, many amino acids can be converted to glucose
-Thus, if needed, protein can help to maintain a steady blood glucose level and serve the
glucose needs of the brain
●Energy-yielding nutrients
-Carbohydrates
-Offer energy
-Fats
-Offer concentrated energy
-Proteins
-offer energy
-offer nitrogen
●Glucose is stored as glycogen
●Fat is stored as triglycerides
●There is no specialized protein energy-storage compound
-When protein-sparing energy from carbohydrate and fat is lacking and the need becomes
urgent the body must dismantle its tissue proteins to obtain amino acids for energy
-Thus, energy deficiency (starvation) always incurs wasting of lean body tissue as
well as loss of fat
The Fate of an Amino Acid
●An amino acid that arrives at a cell can be used in one of several ways
-Used to build part of a growing protein
-Altered to make another needed compound
-Dismantled so as to use its amine group to build another amino acid
-Remainder can be used
-for fuel
-converted to glucose or fat
-If the cell is starved for energy and is lacking glucose and fatty acids
-The amine group will be removed and the remainer used for energy
-The amine group will ultimately be excreted as urine
-If the body has a surplus of amino acids and energy
-The amino group will be excreted
-The remainder can be
-Used for energy
-Converted to glucose or fat for storage
●Removal of amine group
-Means the amino acid has been “wasted”
-Wasting occurs when:
-The body does not have enough energy from other sources
-Has more protein than it needs
-Has too much of any single amino acid
-such as from a supplement
-The diet supplies protein of low quality, with too few essential amino acids
●To prevent the wasting of dietary protein and permit the synthesis of needed body
protein
-Dietary protein must be adequate in quantity
-The diet must supply all of the essential amino acids in the proper amounts
-Enough energy-yielding carbohydrate and fat must be present to permit the dietary
protein to be used as such
Consumer Corner: Protein and Amino Acid Supplements
●Clinical dieticians may use supplemental amino acids to help reverse malnutrition in
some critically ill patients
-Not every patient is a candidate for such therapy
-Supplemental amino acids may stimulate inflammation and so worsen some illnesses
●Healthy people who use protein supplements as a replacement for foods can put
themselves in danger
-Especially when used in weight loss diets
-“liquid protein” diets have caused deaths and heart problems
●Tryptophan supplements
-Tryptopohan is a precursor of the neurotransmitter serotonin
-A regulator of sleep, mood, and sensory perception
-Advertised to relieve
-Pain
-Insomnia
-Depression
-DRI committee concludes that high doses of tryptophan may cause
-Sleepiness
-Severe nausea
-Skin disorders
-Not too long ago people who took such tryptophan supplements developed a blood
disorder
-EMS = eosinophilia-myalgia syndrome
-at least 15 supplement takers died
-Contaminants in the supplement were blamed for the disease
-such impurities are still detected in some tryptophan-containing products
currently on the market
●The body is best off using whole proteins
-Breaking them into manageable pieces
-Which are then split a few at a time, simultaneously releasing them into the blood
-This slow assimilation is best because groups of chemically similar amino acids
compete for carriers that absorb them into the blood
-An excess of one amino acid can, at least temporarily, tie up a carrier and disturb
amino acid absorption
-Digestive disturbances, excess water in the digestive tract, and an increased need for
thiamin poses problems from amino acid supplements
●DRI committee reviewed the available research on amino acid supplements
-Found next to no safety research
-unable to set Tolerable Upper Intake Levels
-Until research becomes available
-no level of amino acid supplementation can be assumed safe for all people
●Growth or altered metabolism makes the following groups of people especially
vulnerable to harm
-All women of child-bearing age
-Pregnant or lactating women
-Infants, children, adolescents, and the elderly
-People with inborn errors of metabolism that affect their bodies’ handling of amino acids
-Smokers
-People on low-protein diets
-People with chronic or acute mental or physical illnesses
●Canada bans the sale of single amino acids to consumers
Food Protein: Quality, Use, and Need
●The body’s response to protein depends on
-The body’s state of health
-Other nutrients and energy taken with the protein
-The protein’s quality
●State of Health
-Malnutrition or infection may greatly increase the need for protein
-While making it hard to eat even normal amounts of food
-Malnutrition
-Secretion of digestive enzymes slows as the tract’s lining degenerates
-Infection
-Extra protein is needed for enhanced immune function
●Protein Quality
-Determines how well a diet supports the growth of children and the health of adults
-Influenced by
-A protein’s digestibility
-A protein’s amino acid composition
Which Kinds of Protein-Rich Foods are Easiest to Digest?
●Digestibility of a protein varies from food to food
-In general, the amino acids from animal sources are more easily digested and absorbed
than those from plant sources
-Animal sources: 90+% digested and absorbed
-Legumes: about 80%-90% digested and absorbed
-Grains and other plant foods: about 70%-90% digested and absorbed
●Food preparation and protein digestibility
-Cooking with moist heat improves protein digestibility
-Cooking with dry heat can impair protein digestibility
Amino Acid Composition
●High-quality proteins
-Dietary proteins containing all of the essential amino acids in relatively the same
amounts that human beings require
-May also contain nonessential amino acids
●Cells need a full array of amino acids from food, their own amino acid pool, or from
both
-Amino acid pool
-Amino acids dissolved in the body’s fluids that provide cells with ready raw
material from which to build new proteins or other molecules
●If the diet fails to supply enough of an essential amino acid
-Cells begin to adjust their activities
-Within a single day of restricted essential amino acid intake, cells begin to conserve it by
-Limiting the breakdown of their working proteins
-Reducing their use of amino acids for fuel
●Limiting Amino Acids can limit Protein Synthesis
-An essential amino acid that is present in dietary protein in an insufficient amount
-Thereby limiting the body’s ability to build protein
-Lack of availability will slow protein synthesis
-When the limiting amino acid again become abundant cells resume their normal
protein-related activities
-If the shortage is chronic cells begin to break down their protein-making machinery
-Thus, when protein intake becomes adequate protein synthesis will lag until the
protein-making machinery can be rebuilt
-Until then, cells function less and less efficiently
●Partially completed proteins are not held for completion at a later time
-They are dismantled and the component amino acids are returned to circulation to be
made available to other cells
-If not soon used for protein synthesis, they are stripped of their amine groups and the
residue is used for other purposes
●Complementary Proteins
-Two or more proteins whose amino acid assortments complement each other in such a
way that the essential amino acids missing from one are supplied by the other
-Mutual supplementation
-The strategy of combining two incomplete protein sources so that the amino
acids in one food make up for those lacking in the other food
●Protein digestibility-corrected amino acid score (PDCAAS)
-A measuring tool used to determine protein quality
-Reflects a protein’s digestibility as well as the proportions of amino acids that it provides
●100-0 scale
100: egg white, ground beef, tuna fish, etc.
-Protein sources that are most readily digested and most perfectly balanced for
meeting human needs
94: soybean
60s-50s: most legumes
25: wheat protein; gluten, formed during bread making
● %Daily Value for protein
-On food labels
-Manufacturers that list values for protein on food labels must use the PDCAAS to
determine the protein quality of their products
Protein Requirements
●Recommended Dietary Allowance
= 0.8 grams per kg of body weight
-Insufficient for active individuals
1.2 g/kg – Active Individual
1.2-1.6 g/kg – Strength Athletes
1.2-1.8 g/kg – Endurance Athletes
weight in lbs / 2.2 = weight in kg
Sedentary Adult: 0.8 g/kg (0.4 g/lb)
Recreational exerciser, adult: 1.0-1.5 g/kg (0.5-0.75 g/lb)
Competitive athlete: 1.2-1.8 g/kg (0.6-0.9 g/lb)
Growing teenage athlete: 1.8-2.0 g/kg (0.9-1.0 g/lb)
UL for ESPE 150 purposes 1.8 g/kg
Adult building muscle mass: 1.4-1.8 g/kg (0.7-0.9 g/lb)
Athlete restricting calories: 1.4-2.0 g/kg (0.7-1.0 g/lb)
Maximum usable amount for adults: 2.0 g/kg (1.0 g/lb)
●Nitrogen Balance
-The amount of nitrogen consumed compared with the amount excreted in a given time
period
-Studies of nitrogen balance underlie the DRI Committee’s recommendations
●Under normal circumstances, healthy adults are in nitrogen equilibrium = zero balance
- Nitrogen in = nitrogen out
●Positive nitrogen balance
- Nitrogen in > nitrogen out
●Negative nitrogen balance
- Nitrogen in < nitrogen out
●Growing children add new blood, bone, and muscle cells to their bodies every day
-Must have more protein, and more nitrogen, in their bodies at the end of each day than
they had at the beginning
-A growing child is in positive nitrogen balance
-As is a pregnant woman
●Negative nitrogen balance
-Occurs when muscle or other protein tissue is broken down and lost
-Illness or injury trigger the release of messengers that signal the body to break
down some of the less vital proteins
-Floods the blood with amino acids and energy needed to fuel the body’s defenses
and fight the illness
Protein Deficiency and Excess
●Protein deficiencies, along with energy deficiencies, are the world’s leading form of
malnutrition
●Health effects of too much protein are less well known
What Happens when People Consume Too Little Protein?
●Protein-energy malnutrition (PEM)
-World’s most widespread malnutrition problems
-Includes both marasmus and kwashiorkor and states in which they overlap
-a.k.a. protein-calories malnutrition (PCM)
-Over 500 million children face imminent starvation and suffer the effects of severe
malnutrition and hunger
-The physiological craving for food
-The progressive discomfort, illness, and pain resulting from the lack of food
-Most of the 33,000 children who die each day are malnourished
-Prevalent in Africa, central America, South America, the Middle East, East and
Southeast Asia
-Developing countries, including those in North America, are not immune to it
●Marasmus
-Chronic inadequate food intake
-Inadequate energy, vitamin, mineral, and protein intake
-Person is shriveled and lean all over
-Occurs most commonly in children from 6-18 months of age in overpopulated city slums
-Children in impoverished nations subsist on a weak cereal drink with scant energy and
protein of low quality
-Such food can barely sustain life
-A starving child often looks like a wizened little old person
-Just skin and bones
-Without adequate nutrition
-Muscles, including the heart muscles, waste and weaken
-Brain development is stunted
-learning is impaired
-Metabolism is so slow that body temperature is subnormal
-Little or no fat under the skin to insulate against the cold
-Child engages in as little physical activity as possible
-not even crying for food
-Body cuts down on any expenditure of protein not needed for the heart, lungs, and brain
to function
-Growth ceases
-Skin loses its elasticity and moisture
-Tends to crack, sores develop and fail to heal
-Digestive enzymes are in short supply
-Digestive tract lining deteriorates and absorption fails
-Blood proteins including hemoglobin, are no longer produced
-Child becomes anemic and weak
-Lack the protein needed to heal a broken bone
-Antibodies are degraded to provide amino acids for other uses leaving the child an easy
target for infection
-Dysentary
-An infection of the digestive tract that causes diarrhea
-Depletes the body of nutrients, especially minerals
-Measles
-Might make a healthy child sick for 1-2 weeks
-Kills a child with PEM within 2-3 days
●Once an infection sets in kwashiorkor often follows and the immune system weakens
further
●Infections that occur with malnutrition are responsible for two-thirds of the deaths of
young children in developing nations
●Ultimately, marasmus progresses to the point of no return
-The body’s machinery for protein synthesis, itself made of protein, has been degraded
-At this point, attempts to prevent by giving food or protein fail
●Kwashiorkor
-Swollen belly and skin rash are present
-Severe acute malnutrition
-Too little protein to support body functions
-Symptoms resemble those of marasmus
-Often without sever wasting of body fat
-Proteins and hormones that previously maintained fluid balance are diminished
-Fluids leak out of the blood and accumulate in the belly and legs
-Causing edema
-Belly often bulges with a fatty liver
-Caused by lack of the protein carriers that transport fat out of the liver
-Fatty liver loses some of its ability to clear poisons from the body,
prolonging their toxic effects
-Without sufficient tyrosine to make melanin, the child’s hair loses its normal color
-Inadequate protein synthesis leaves the skin patchy and scaly
-Sores fail to heal
-In countries where kwashiorkor is prevalent, each baby is weaned from breast milk as
soon as the next one comes along
-The older baby no longer receives breast milk, which contains high-quality
protein
-Instead is given a watery cereal with scant protein of low quality
-Rare in the United States, but not totally unknown
●Marasmus and kwashiorkor can occur in combination
●If caught in time, the starvation of a child can be reversed by careful nutrition therapy
-Fluid balances are most critical
-Diarrhea will have depleted the body’s potassium
-And upset other electrolyte balances
-Electrolyte imbalances, anemia, fever, and infection often lead to heart failure
and sudden death
-Correction of fluid and electrolyte balances usually raises blood pressure and
strengthens the heartbeat within a few days
●Later, fat-free milk, providing protein and carbohydrate, can safely be given
-Fat is introduced later
-When body protein is sufficient to provide carriers
●Years after PEM is corrected a child may often experience deficits in thinking and
school achievement compared with well-nourished peers
●PEM at Home
-Occurs among some groups in the United States and Canada
-The poor living
-On U.S. Indian reservations
-In inner cities
-In rural areas
-Many elderly people
-Hungry and homeless children
-Those suffering from anorexia nervosa
-Some well-meaning but misinformed parents have inflicted PEM and other deficiency
diseases on their toddlers by replacing their milk with uneriched, protein-poor “heath
food” soy or rice drinks
●At risk for PEM
-Those with wasting diseases
-Such as AIDS and cancer
-Those addicted to drugs and alcohol
●PEM and serious illnesses worsen each other
-Treating the PEM often reduces medical complications and suffering even when the
underlying disease is untreatable
●In the U.S.
-Millions of people who work to support their children cannot afford nutritious food
-Well over 2.5 million children go hungry at least some of the time
●Hunger, especially in children, threatens everyone’s future
●Hungry children:
-Do not learn as well as fed children
-Are not as competitive
-Are ill more often
-have higher absentee rates from school
-When they attend they cannot concentrate for long
Is It Possible to Consume Too Much Protein?
●DRI committee recommendations
-Diet should include no more than 35% of calories from protein
-To decrease risk of chronic diseases
●Overconsumption of protein
-No health benefits
-May pose health risks for the
-Heart
-Kidneys
-Bones
●Diets high in protein-rich foods
-Often associated with obesity
-And its many accompanying health risks
-Animal protein sources in particular can be high in saturated fat
-A known contributor to atherosclerosis and heart disease
-The effect of animal protein itself on the heart health is uncertain
-Substituting plant protein for animal protein improves indicators of heart
disease risk
●Animals fed experimentally on high-protein diets
-Often develop enlarged kidneys or livers
●In human beings
-A high-protein diet worsens existing kidney problems and may accelerate a decline in
only mildly impaired kidneys
-One of the most effective treatments for people with established kidney problems
is to reduce protein intakes to slow the progression of their disease
-Diets high in protein, particularly animal protein, correlate with a higher incidence of hip
fractures in some populations
●No one yet knows exactly what percentage of dietary protein is hazardous
-Meat-eating Alaskans typically consume less than 50% of calories from protein
-Average protein intake in U.S. Adult men is about 16% of calories
-but people typically take in way too many calories, so this is a lot more
than it sounds
-Popular low-carbohydrate, high protein weight loss diets often suggest up to 65% of
energy from protein
Getting Enough But Not Too Much Protein
●People in developed nations usually eat more than enough protein
●Protein-rich foods
-Contribute an abundance of high-quality protein
-Meat, poultry, fish, legumes, eggs, and nuts group
-Milk, yogurt, and cheese group
-Contribute smaller amounts of protein that can add up to significant quantities
-Vegetables group
-Grains group
●The Advantages of Legumes
-The protein of some legumes is of a quality almost comparible to that of meat
-For practical purposes, the quality of soy protein can be considered the
equivalent to that of meat
-Excellent sources of
-B vitamins
-Iron
-Calcium and other minerals
-Lack
-Vitamin A
-Vitamin C
-Vitamin B12
-not found in meats either
-found in fruits and vegetables
Controversy: Vegetarian and Meat-Containing Diets
●In affluent countries those who eat well-planned vegetarian diets
-Obesity rates ↓
-Heart Disease Rates ↓
-High Blood Pressure Rates ↓
-Cancer Rates ↓
-Lifespan↑
●Positive Health Aspects of Vegetarian Diets
-There is strong evidence linking vegetarian diets with reduced incidences of chronic
diseases
-In addition to not eating meat, vegetarians often have increased intakes of fruits
and vegetables
-Primary contributors of nutrients and phytochemicals
●Vegetarian Diets often contain more
-Fiber
-Potassium
-Several vitamins associated with reduced disease risk
●With exceptions, vegetables typically
-Use no tobacco
-use alcohol in moderation if at all
-may be more physically active than other adults
●Vegetarian Diets and Weight Control
-Body weight are higher for people eating a mixed diet than for vegetarians
-Weight increases as frequency of meat consumption increases
-Lower body weights correlate with
-Higher intakes of fiber
-Lower intakes of fat
●Vegetarians and Heart Disease
-People consuming plant-based diets die less often from heart disease and related
illnesses than do meat-eating people
●Vegetarians may lower disease risk by virtue of their phytochemicals
-For example, the phytochemical of soy products help lower cholesterol
-Can help lower LDL, triglycerides
●A few nutrients of interest
-Any diet, if not properly balanced, can lack nutrients
-Poorly planned vegetarian diets typically lack
-Iron
-Vitamin B12
-Zinc
-Vitamin D
-Calcium
-Protein
●Poorly planned meat eater’s diet may lack
-Vitamin A
-Vitamin C
-Folate
-Fiber
-Etc.
●Different Types of Vegetarians
Fruitarian – includes only raw or dried fruits, seeds, and nuts in the diet
Macrobiotic diet – a vegan diet composed mostly of whole grains beans, and certain
vegetables; taken to extremes, macrobiotic diets have resulted in malnutrition and
even death
Vegan – includes only food from plant sources: vegetables, grains, legumes, fruits, seeds,
and nuts; also called strict vegetarian
Lacto-vegetarian – includes dairy products, vegetables, grains, legumes, fruits, and nuts;
excludes flesh, seafood, and eggs
Lacto-ovo-vegetarian – includes dairy products, eggs, vegetables, grains, legumes, fruits,
and nuts; excludes flesh and seafood
Ovo-vegetarian – includes eggs, vegetables, grains, legumes, fruits, and nuts; excludes
flesh, seafood, and milk products
Pesco-vegetarian – same as partial vegetation, but eliminates poultry
Partial vegetarian – a term sometimes used to mean an eating style that includes seafood,
poultry, eggs, dairy products, vegetables, grains, legumes, fruits, and nuts;
excludes or strictly limits certain meats, such as red meats
Vegetarian – includes plant-based foods and eliminates some or all animal-derived foods
●Vegetarian Diets and Defense Against Cancer
-Vegetarians have significantly lower rates of certain cancers than the general population
-May be associated more with the abundance of fruits and vegetables in the diet
than with the exclusion of all products
●Colon cancer appears to correlate with moderate-to-high intakes of
-Alcohol
-Total food energy
-Fatty red meats and processed meats
-But not poultry or fish
-Such a diet may also be positively associated with stomach cancer
●Colon Cancer may possibly be correlated with
-High intakes of refined grains
-Low intakes of whole grains
-Low intakes of vitamin D
●Colon cancer risk evidence is mixed on
-Low intakes of fruits and vegetables