Download Chapter 1 – Title of Chapter

Chapter 6 – Protein: Amino Acids
Learning Objectives
After completing Chapter 6, the student will be able to:
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Describe how the chemical structure of proteins differs from the structures of carbohydrates and fats.
List the 9 essential amino acids.
Trace the digestion of protein and list the enzymes needed to complete the process.
Explain the process used by the body to synthesize new proteins.
List the major functions of protein in the body.
Describe nitrogen balance and provide examples of positive nitrogen balance, negative nitrogen balance, and equilibrium.
Describe deamination, where it occurs in the body, the products produced, and the fate of these products.
Discuss the factors used to evaluate protein quality.
Describe the diseases that result from inadequate intake of protein and protein-kcalories.
Discuss the health effects of over-consumption of protein.
Calculate the protein needed daily using the RDA for protein.
Discuss the health risks of protein and amino acid supplements.
Define nutritional genomics and explain its potential uses in health care.
Outline
I. The Chemist’s View of Proteins
Proteins are made from 20 different amino acids, 9 of which are essential. Each amino acid has an
amino group, an acid group, a hydrogen atom, and a side group. It is the side group that makes each
amino acid unique. The sequence of amino acids in each protein determines its unique shape and
function.
A. Amino Acids
1. Amino acids have unique side groups that result in differences in the size, shape, and
electrical charge of an amino acid.
2. Nonessential amino acids, also called dispensable amino acids, are ones the body can create.
Nonessential amino acids include alanine, arginine, asparagines, aspartic acid, cysteine,
glutamic acid, glutamine, glycine, proline, serine, and tyrosine.
3. Essential amino acids, also called indispensable amino acids, must be supplied by the foods
people consume. Essential amino acids include histidine, isoleucine, leucine, lysine,
methionine, phenyalanine, threonine, tryptophan, and valine.
4. Conditionally essential amino acids refer to amino acids that are normally nonessential but
essential under certain conditions.
B. Proteins
1. Amino acid chains are linked by peptide bonds in condensation reactions.
a. Dipeptides have two amino acids bonded together.
b. Tripeptides have three amino acids bonded together.
c. Polypeptides have more than two amino acids bonded together.
2. The sequence of amino acids that determines the structure of a protein varies greatly. Unlike
carbohydrates, which are composed of chains of glucose, proteins can be composed of up to
20 different amino acids.
3. Weak electrical attractions within a polypeptide chain determine the secondary structure of
proteins.
4. Polypeptide Tangles – Tertiary Structure
a. Hydrophilic side groups are attracted to water.
b. Hydrophobic side groups repel water.
c. The shape of a protein provides stability.
5. Multiple Polypeptide Interactions – Quaternary Structures
a. Some polypeptides function independently.
b. Some polypeptides need to combine with other polypeptides to function correctly.
c. An example of a quaternary structure is hemoglobin, which is composed of 4 polypeptide
chains.
6. Protein denaturation is the uncoiling of protein that changes its ability to function.
a. Proteins can be denatured by heat and acid.
b. After a certain point, denaturation cannot be reversed.
II. Digestion and Absorption of Protein
Stomach acid and enzymes facilitate the digestion of protein. It is first denatured, then broken down
to polypeptides. The small intestine continues to break down protein into smaller peptides and amino
acids so it can be absorbed.
A. Protein Digestion
1. In the Stomach
a. Protein is denatured by hydrochloric acid.
b. Pepsinogen (a proenzyme) is converted into its active form pepsin in the presence of
hydrochloric acid.
c. Pepsin cleaves proteins into smaller polypeptides.
2. In the Small Intestine
a. Proteases hydrolyze protein into short peptide chains called oligopeptides, which contain
four to nine amino acids.
b. Peptidases split proteins into amino acids.
B. Protein Absorption
1. Used by intestinal cells for energy or synthesis of necessary compounds.
2. Protein is transported to the liver.
3. Taking enzyme supplements or consuming predigested proteins is unnecessary.
III. Proteins in the Body
Proteins are versatile and unique. The synthesis of protein is determined by genetic information.
Protein is constantly being broken down and synthesized in the body. Researchers measure nitrogen
balance to study synthesis, degradation, and excretion of protein. Protein has many important
functions in the body. Protein can be used for energy if needed; its excesses are stored as fat. The
study of proteins is called proteomics.
A. Protein Synthesis
1. Synthesis is unique for each human being and is determined by the amino acid sequence.
2. Delivering the instructions through messenger RNA
a. Carries a code to the nuclear membrane and attaches to ribosomes.
b. Presents a list to make a strand of protein.
3. Transfer RNA lines up the amino acids and brings them to the messenger.
4. Sequencing errors can cause altered proteins to be made. An example is sickle-cell anemia
where an incorrect amino acid sequence interferes with the cell’s ability to carry oxygen.
5. Nutrients and Gene Expression
a. Cells regulate gene expression to make the type of protein needed for that cell.
b. Epigenetics refers to a nutrient’s ability to activate or silence genes without interfering
with the genetic sequence.
B. Roles of Proteins
1. Building Materials for Growth and Maintenance
a. A matrix of collagen is filled with minerals to provide strength to bones and teeth.
b. Replaces tissues including the skin, hair, nails, and GI tract lining.
2. Enzymes are proteins that facilitate anabolic (building up) and catabolic (breaking down)
chemical reactions.
3. Hormones regulate body processes and some hormones are proteins. An example is insulin.
4. Regulators of Fluid Balance
a. Plasma proteins attract water.
b. Maintain the volume of body fluids to prevent edema, which is excessive fluid.
c. Maintain the composition of body fluids.
5. Acid-Base Regulators
a. Act as buffers by keeping solutions acidic or alkaline.
b. Acids are compounds that release hydrogen ions in a solution.
c. Bases are compounds that accept hydrogen ions in a solution.
d. Acidosis is high levels of acid in the blood and body fluids.
e. Alkalosis is high levels of alkalinity in the blood and body fluids.
6. Transporters
a. Carry lipids, vitamins, minerals and oxygen in the body.
b. Act as pumps in cell membranes, transferring compounds from one side of the cell
membrane to the other.
7. Antibodies
a. Fight antigens, such as bacteria and viruses, which invade the body.
b. Provide immunity to fight an antigen more quickly the second time exposure occurs.
8. Source of energy and glucose if needed.
9. Other Roles
a. Blood clotting by producing fibrin, which forms a solid clot.
b. Vision by creating light-sensitive pigments in the retina.
C. A Preview of Protein Metabolism
1. Protein Turnover and the Amino Acid Pool
a. Protein turnover is the continual making and breaking down of protein.
b. Amino acid pool is the supply of amino acids that are available.
1. Amino acids from food are called exogenous.
2. Amino acids from within the body are called endogenous.
2. Nitrogen Balance
a. Zero nitrogen balance is nitrogen equilibrium, when input equals output.
b. Positive nitrogen balance means nitrogen consumed is greater than nitrogen excreted.
c. Negative nitrogen balance means nitrogen excreted is greater than nitrogen consumed.
3. Using Amino Acids to Make Other Compounds
a. Neurotransmitters are made from the amino acid tyrosine.
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b. Tyrosine can be made into the melanin pigment or thyroxine.
c. Tryptophan makes niacin and serotonin.
Using Amino Acids for Energy and Glucose
a. There is no readily available storage form of protein.
b. Breaks down tissue protein for energy if needed.
Using Amino Acids to Make Fat
a. Excess protein is deaminated and converted into fat.
b. Nitrogen is excreted.
Deaminating Amino Acids
a. Nitrogen-containing amino groups are removed.
b. The two products that result from deamination include ammonia and keto acids.
Using Amino Acids to Make Proteins or Nonessential Amino Acids
a. Cells can assemble amino acids into the protein needed.
b. Transamination involves transferring an amino group to a keto group.
Converting Ammonia to Urea – Ammonia and carbon dioxide are combined in the liver to
make urea.
Excreting Urea
a. Ammonia is converted to urea in the liver.
b. The kidneys filter urea out of the blood.
c. Increased water intake is necessary with a high-protein diet to flush the excess urea from
the body.
IV. Protein in Foods
Eating foods of high-quality protein is the easiest way to get all the essential amino acids.
Complementary proteins can also supply all the essential amino acids. A diet inadequate in any of the
essential amino acids limits protein synthesis. The quality of protein is measured by its amino acid
content, digestibility, and ability to support growth.
A. Protein Quality
1. Digestibility
a. Depends on protein’s food source
1. Animal proteins are 90%-99% absorbed.
2. Plant proteins are 70%-90% absorbed.
3. Soy and legumes are 90% absorbed.
b. Other foods consumed at the same time can change the digestibility.
2. Amino Acid Composition
a. The liver can produce nonessential amino acids.
b. Cells must dismantle to produce essential amino acids if they are not provided in the diet.
c. Limiting amino acids are those essential amino acids that are supplied in less than the
amount needed to support protein synthesis.
3. Reference protein is the standard by which other proteins are measured. Based on their needs
for growth and development, preschool children are used to establish this standard.
4. High-Quality Proteins
a. Contains all the essential amino acids.
b. Animal foods contain all the essential amino acids.
c. Plant foods are diverse in content and tend to be missing one or more essential amino
acids.
5. Complementary Proteins
a. Combining plant foods that together contain all the essential amino acids.
b. Used by vegetarians.
B. Protein Regulation for Food Labels
1. List protein quantity in grams.
2. % Daily Values is not required but reflects quantity and quality of protein using PDCAAS.
V. Health Effects and Recommended Intakes of Protein
Protein deficiency and excesses can be harmful to health. Protein deficiencies arise from proteindeficient diets and energy-deficient diets. This is a worldwide malnutrition problem, especially for
young children. High-protein diets have been implicated in several chronic diseases.
A. Protein-Energy Malnutrition (PEM) – Those with chronic PEM are short for their age,
whereas those with acute PEM are underweight for their height.
1. Classifying PEM – a. May have maramus, kwashiorkor, or a combination of the two.
2. Marasmus
a. Infancy, 6 to 18 months of age.
b. A severe deprivation or impaired absorption of protein, energy, vitamins and minerals.
c. Develops slowly.
d. A severe weight loss and muscle wasting, including the heart.
e. < 60% weight-for-age.
f. Anxiety and apathy.
g. Good appetite is possible.
h. Hair and skin problems.
3. Kwashiorkor
a. Older infants and young children, 18 months to 2 years of age.
b. Inadequate protein intake, infections.
c. Rapid onset.
d. Some muscle wasting, some fat retention.
e. Growth is 60%-80% weight-for-age.
f. Edema and fatty liver.
g. Apathy, misery, irritability and sadness.
h. Loss of appetite.
i. Hair and skin problems.
4. Marasmus-Kwashiorkor Mix
a. Both malnutrition and infections.
b. Edema of kwashiorkor.
c. Wasting of marasmus.
5. Infections
a. Lack of antibodies to fight infections.
b. Fever.
c. Fluid imbalances and dysentery.
d. Anemia.
e. Heart failure and possible death.
6. Rehabilitation
a. Nutrition intervention must be cautious, slowly increasing protein.
b. Programs involving local people work better.
B. Health Effects of Protein
1. Heart Disease
a. Foods high in animal protein also tend to be high in saturated fat.
b. Homocysteine levels increase cardiac risks.
c. Arginine may protect against cardiac risks.
2. Cancer – A high intake of animal protein is associated with some cancers.
3. Adult Bone Loss (Osteoporosis)
a. High protein intake associated with increased calcium excretion.
b. Inadequate protein intake affects bone health also.
4. Weight Control
a. High-protein foods are often high-fat foods.
b. Protein at each meal provides satiety.
c. Adequate protein, moderate fat, and sufficient carbohydrate better support weight loss.
5. Kidney Disease
a. High protein intake increases the work of the kidneys.
b. Does not seem to cause kidney disease.
C. Recommended Intakes of Protein
1. 10%-35% energy intake.
2. Protein RDA
a. 0.8 g/kg/day for most adults.
b. 1.2-1.7 g/kg/day for athletes.
3. Adequate Energy
a. Must consider energy intake.
b. Must consider total grams of protein.
4. Protein intake in abundance is common in the U.S. and Canada.
D. Protein and Amino Acid Supplements
1. Many reasons for supplements.
2. Protein powders have not been found to improve athletic performance.
a. Whey protein is a waste product of cheese manufacturing.
b. Purified protein preparations increase the work of the kidneys.
3. Amino acid supplements are not beneficial and can be harmful.
a. Branched-chain amino acids provide little fuel and can be toxic to the brain.
b. Lysine appears safe in certain doses.
c. Tryptophan has been used experimentally for sleep and pain, but may result in a rare
blood disorder.
VI. Highlight: Nutritional Genomics
In the future, genomics labs may be used to analyze an individual’s genes to determine what diseases
the individual may be at risk for developing. Nutritional genomics involves using a multidisciplinary
approach to examine how nutrition affects genes in the human genome.
A. A Genomics Primer
1. Human DNA contains 46 chromosomes made up of a sequence of nucleotide bases.
2. Microarray technology is used to analyze gene expression.
3. Nutrients are involved in activating or suppressing genes without altering the gene itself.
4. Epigenetics is the study of how the environment affects gene expression.
5. The benefits of activating or suppressing a particular gene are dependent upon the gene’s role.
B. Genetic Variation and Disease
1. Small differences in individual genomes.
2. May affect a disease’s ability to respond to dietary modifications.
3. Nutritional genomics would allow for personalization of recommendations.
4. Single-Gene Disorders
a. Mutations cause alterations in single genes.
b. Phenylketonuria is a single-gene disorder that can be affected by nutritional intervention.
5. Multigene Disorders
a. Multiple genes are responsible for the disease.
b. Heart disease is a multigene disorder that is also influenced by environmental factors.
c. Genomic research may be helpful in guiding treatment choices.
d. Variations called single nucleotide polymorphisms (SNPs) may influence an individual’s
ability to respond to dietary therapy.
C. Clinical Concerns
1. An increased understanding of the human genome may impact health care by:
a. Increasing knowledge of individual disease risks.
b. Individualizing treatment.
c. Individualizing medications.
d. Increasing knowledge of nongenetic causes of disease.
2. Some question the benefit of identifying individual genetic markers.
3. Even if specific recommendation can be made based on genes, some may choose not to follow
recommendations.
Case Study1
Erin is a 28-year-old professional woman who is 5 feet 8 inches tall and vigilantly maintains her weight
at 118 pounds by following a lacto-ovo (non-fat milk and egg whites only) vegetarian diet that supplies
approximately 1200 calories a day. With her understanding that protein should provide between 10 and
35 percent of her daily calories, she reasons that her daily intake of 40 grams of protein from milk, eggs,
legumes, and nuts is adequate for her needs. She is concerned, however, that she has been sick more than
usual and has experienced two stress fractures in her leg over the past three years while exercising.
1. Explain why Erin’s assumptions about her protein needs are unrealistic based on her current weight.
2. Assuming a healthy weight for Erin is 141 pounds, use the information from Box 6-1 of this chapter
to calculate her recommended daily protein requirement. Show your calculations.
3. What percentage of Erin’s energy comes from protein? Is this adequate? Why or why not?
4. Erin’s energy needs for a healthy weight are closer to 1600 calories a day. What are some
consequences of her low calorie intake on her body’s need for protein?
5. How does Erin’s low intake of calories and protein contribute to her risk for osteoporosis?
6. Assuming Erin consumes 20 grams of protein from whole grains, vegetables, and legumes each day,
calculate how she can meet the remainder of her protein needs with dairy foods and egg whites.
Answer Key
1. Protein needs are based on “healthy body weight.” Erin is underweight so her actual weight is not a
good parameter for calculating her protein needs.
2. RDA for protein = Weight in kg x 0.8 = 64 kg x 0.8 grams per kg = 51 grams protein per day.
3. 40 grams protein x 4 kcal per gram = 160 kcalories divided by 1200 kcalories per day = 13.3% of her
daily calories from protein. Although this falls into the recommended percentage of calories from
protein, it is not adequate because the requirement for protein assumes that adequate calories to meet
dietary needs are consumed. Erin is consuming inadequate calories.
4. An inadequate intake of calories forces the body to use protein to meet energy needs and less is left to
meet the body’s protein needs. Immune function and bone loss are two important consequences of
inadequate protein.
5. Protein as well as calcium is needed for bone health. When calories are restricted, essential protein is
used for energy needs and less is available for essential functions like synthesis of collagen, the
primary protein in bone.
6. 3 cups milk x 8 grams protein per cup = 24 grams protein + 1 egg white = 7 grams protein = 31 grams
+ 20 grams from vegetables, legumes, and vegetables = 51 grams protein per day.
How to Calculate Recommended Protein Intakes
The student should first determine the weight to use: her or his weight in kg if within the healthy BMI
range, or if not, then the weight at the midpoint of the healthy BMI range for a person of her/his height.
The student should then multiply her or his weight in kg by 0.8 g/kg to determine the protein RDA. For
example, a student who is 5’6” and weighs 115 lb. (BMI = 18.6) would use his/her current weight and
calculate an RDA of 42 g protein per day.
Critical Thinking Questions
These questions will also be posted to the book’s website so that students can complete them online and
e-mail their answers to you.
1. Discuss the three differences between proteins and carbohydrates/fats. Articulate why these
differences are important.
Answer: 1.) Proteins contain a nitrogen group along with carbons, oxygen, and hydrogen. These
nitrogen molecules become part of the amino group, distinguishing proteins from carbohydrates and
fats. This part of the protein is eventually excreted as urea, a process that requires additional work of
the kidneys, one limiting factor in overconsumption of proteins.
2.) Proteins are very complex molecules that have primary, secondary, tertiary, and quaternary
structures. Because they are much larger molecules than carbohydrates and fats, they are able to fold
and configure themselves in unique ways. This allows them to perform many functions that are not
performed by carbohydrates and fats.
3.) Given the above, proteins are very susceptible to acid and heat and can be denatured readily. A
denatured protein is not able to perform its given function. While fats can become rancid, neither fats
nor carbohydrates become denatured in such a manner as to render them unable to perform their
unique tasks or functions.
4.) Also unique to proteins is their many functions as enzymes, fluid and acid/base regulators,
transporters, antibodies, or parts of the body such as skin, muscle, or bones.
2. List the roles of proteins in the body and detail the importance of each role identified.
Answer: Growth and Maintenance of Body Tissues: One of the major roles for which proteins are
noted or known is providing for growth and development of body tissues such as the muscles, skin,
hair, etc. Proteins are also important in the repair of body tissues that are damaged or require
replacement. Most consumers identify proteins with this function in the body; however, proteins have
many more functions in the human body.
Functioning as Enzymes: Enzymes are important molecules in our bodies that are required for the
many chemical reactions that release energy and allow our bodies to function. All enzymes are made
of proteins; therefore, without protein, our bodies would be unable to carry out the chemical reactions
required for life.
Maintenance of Fluid Balance: Fluid balance in and out of cells and within the blood is maintained by
proteins. Proteins are very large molecules that do not normally cross cellular membranes. However,
in times of critical illness, proteins are able to leak out, attracting water to themselves and causing a
build-up of fluid or edema. When there is edema, the vascular system is less functional in its ability to
carry all nutrients as well as oxygen around the body; therefore, the entire body becomes deprived of
oxygen and nutrients. When this happens, depending on the length of time the situation lingers,
tissues can and will die.
Maintenance of Acid-Base Balance: In the normal course of daily events of the body, the body works
hard to maintain homeostasis. Proteins are an important part of this process through their work in
maintaining acid-base balance. Proteins do so by attracting positively charged ions from hydrogen
molecules to their negatively charged surfaces. Proteins can release these negative charges elsewhere
in a basic environment, protecting themselves from denaturation.
Transportation of Many Substances throughout the Body: Proteins are especially good transporters of
many substances, including nutrients such as vitamins and minerals, lipids (i.e., the lipoproteins),
oxygen such as in hemoglobin, etc. Proteins are very large, complex, and multidimensional, allowing
them to function in a variety of ways, some of which we are still discovering. In this regard, their role
in transportation of nutrients about the body may still teach us more about the fundamentals of
nutrition and micronutrient utilization.
Function as Antibodies: Antibodies are large protein molecules that are made by our bodies to help us
fight against a particular disease or illness that is viral in nature. When an individual becomes ill with
a virus, the virus leaves in the body materials or particles that are called antigens. Antigens are
informational units about the virus that allow the body to make an antibody that can help the body
fight against that particular virus with greater strength and speed. These antibodies are made of
proteins from the body. Once the body has fought the disease, the work in producing the antibody
from the antigen leaves behind memory information that stays in the body forever, producing
“immunity” to that specific virus in the future. In this manner, each person’s body has a unique and
wonderful ability to manufacture its own fighting army for viruses with proteins, for the most part!
The body, of course, must be healthy and well nourished, and there are times when viruses (like
AIDS) outwit our body’s unique defenses.
Role in Energy: As discussed in earlier chapters, the body can break down protein to serve as a source
of glucose and energy when needed. While there are many other more important roles for protein and
utilizing protein for energy can be costly to those other roles, protein will be supplied as an energy
source in times of need. In these cases, protein can be taken from the cells, body tissues, etc.
Other: Protein does serve in many other roles via its role in chemical reactions. For example, as
outlined in your text, a cascade of events is required for the formation of a blood clot. A few of these
events include the formation of fibrin, which is a stringy glob of protein fibers that will eventually
lead to a collagen scar. Protein is also involved in vision, a sequence of events in which light
permeates the cells of the retina. The protein molecule opsin responds to the light and decides how
much light it will allow into the eye by changing the shape of the retina.
Clearly, protein is multifunctional, and vastly important to our bodies. I hope the student is able to
gain a better understanding of the depth and breath of the role of protein in human function.
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Many Americans consume beyond the RDA for protein. However, there are many individuals that have difficulty
acquiring enough food to feed themselves and their families, or are simply unable to eat enough to meet the RDA for
protein. Many times, individuals having difficulty financially may consume inexpensive staples or leftovers from others.
Discuss how the RD would go about assessing such an individual’s protein status. What suggestions would you have for
this person to improve his/her protein intake and balance?
Answer: The average American eats about 100 grams of protein/day compared to a recommended 50-60 grams,
depending on gender and activity level (for those over 25 years). While protein intake is generally not a problem in
American culture, there are enough cases of protein malnutrition and individuals that are unable to consume high-quality
proteins in their diets that this question is posed to assist the student in understanding the broad array of individuals they
may come into contact with as practitioners.
The RD would generally perform multiple types of assessment to attain the best data for their decision making. Therefore,
the RD might investigate the following:
Dietary History: A food frequency and a three-day diet recall—with these assessments the RD is looking for types of
protein eaten. The RD would want to determine the quality of the protein, the frequency through an average week, and the
amount. Does the individual have to combine proteins to make sure they are consuming all essential amino acids? Are
they eating enough protein for their age, gender, weight, and height? Are they a member of a high-risk group that should
be supplemented (i.e., pregnant, breast feeding, elderly, etc.)?
Social/Behavior History: Does the client eat alone? Do they have any relatives or friends that can help with their dietary
issues? Have they had diet problems in the past? Do religion or cultural beliefs affect their diet? Has the client lost any
significant others in the recent past? Etc.
Medical History: Does the client have any significant medical problems/issues that affect their diet or ability to eat? Have
they in the recent past? Are they on medications that affect their ability to eat? Drug-nutrient interactions? Wounds?
Wound healing issues? Loss of hair, edema? What does their N-balance study show? Are they in N-balance? Was the
client assessed for protein malnutrition? Albumin? Do they have a history of heart disease, cancer, and bone disease? Any
other diseases?
Physical Assessment: What does the client look like to you? Do they look tired? Does their skin look dry? What about the
turgor? Do they have edema? Is their hair thin, or are their nails weak? Do they have any unhealed wounds?
The goal here is for the student to pursue a full assessment of the client in an effort to acquire the most accurate
information possible. While the student may list other types of information, what is important is that the student pursues
multiple areas of assessment in an effort to ensure that they have many means of assessing protein intake and metabolism.
Recommendations for the client might be as follows: Inexpensive yet nutrient-rich sources of protein can include such
food staples as peanut butter and legumes, and using powdered milk and oatmeal in meals such as meatloaf and
hamburgers. Also advising that a client utilize a food pantry, where such staples can be secured freely or for minimal cost,
can stretch a budget a long way. Adding powdered milk or oatmeal to meat meals can not only stretch the meal but add to
its protein value. This also holds true for adding beans to a meal.
4.
Protein consumption in adults could be considered a form of substance abuse in the U.S. Why might this statement be
true, and what are the health consequences of protein overconsumption?
Answer: As stated above, in the United States, consumers eat much more protein than is required for their bodies. There
might be many reasons for this. One is that most consumers do not understand what an appropriate portion size for a
“protein” is in the United States. Another is that most Americans believe that protein is a miracle nutrient for everything
that ails anyone. Many diets begin with the concept that more protein and less carbohydrate are good because many
individuals have lost the notion that food is fuel for the body, not the next drug of choice. Given that we are fortunate to
have a plentiful supply of food in the United States, food in general might be thought of as an abused substance; however,
of all the nutrient categories, marketers see that protein appears to be the “miracle substance” sought by consumers that
are desperate to win the battle of the bulge.
The need for protein in the body has been thoroughly investigated for many years, and while nutrition is a young science
and more can always be learned, it appears to be fairly clear that the healthy adult body’s need for protein is 0.8 g/kg/day
or about 10-35% of energy intake. Over time, more work has been done on athletes and a higher goal has been established
at 1.2-1.5 g/kg/day for athletes, given that there is much tissue breakdown with training, etc.
The average American consumes 100-200 grams of protein a day. Consumers that adhere to diet fads promoting a high
protein and low carbohydrate intake consume well beyond this. Many consumers are led to believe that carbohydrates are
“bad” and proteins will “make... people thin,” give people energy, and solve all sorts of problems. Advertisements for
protein shakes, powers, pills, drinks, and bars abound. Yet consumers do not seem to understand the real roles of protein
nor its limitations. And because it is a food, it might even be considered safer than a drug. Without hesitation due to their
health, existing health problems, etc., many American consumers will blindly follow a high-protein diet beyond their
already high-protein diet. These diets seem attractive because, in many Americans’ viewpoint, consuming lots of steaks,
eggs, bacon etc. is preferable to eating moderately, exercising, and including fruits and vegetables.
In this manner, protein overconsumption might be analogous to a drug addiction because the individual does not see the
problem as an addiction, the individual will continue to pursue eating high volumes of proteins regardless of their health
history, most individuals cannot go without meat proteins if given an ultimatum, most individuals cannot cut down on
their consumption, and individuals that are meat eaters will indicate that there is no issue with their over consumption
with meat at the volume or level that they are eating this protein. These are all very similar signs to drug addiction.
Overconsumption of protein can be difficult on the body because metabolism of protein requires the excretion of the
nitrogen group, which is the work of the kidneys. With consumption of a great deal of protein, the kidneys must work
much harder to remove the urea from the body. Therefore, while generally protein digestion, absorption, and waste
elimination are not an issue for the body, when large amounts of nitrogen must be removed from the body, this puts a
great stress on the kidneys to remove the urea.
Those that ingest proteins from beef and other fatty sources add additional lipids or fats to their caloric load. If these
calories are not used as energy, the body will store them as fat to be used as future energy. Additional lipids circulated in
the body can result in the formation of plaque in the arteries. It is this plaque that can break free and perhaps result in a
blood clot, a sudden heart attack, or heart failure of a loved one that had previously been healthy. While the continued
build-up of plaque can close the artery and result in the requirement for heart by-pass surgery or the death of tissue distal
to the area where the artery was closed, in more recent years noted celebrities have died suddenly for no apparent reason
from a plaque that was freed, causing a sudden heart attack in an otherwise “healthy” individual.
Protein is a kcalorie-bearing nutrient. The more one eats, the more calories one provides to the body. If calories out are
not balanced with calories in, excess calories are stored as fat. Frequently, individuals on high-protein diets believe that
they will not gain weight. However, excess protein can mean excess calories if no exercise is part of the plan and the
protein consumed is also accompanied with fat. Therefore, it is very important for consumers to understand that they must
balance their calories in protein with exercise and that the best diet includes other types of nutrients, so that they are able
to achieve a balance of all nutrients for optimal health.
5.
The science of proteomics has allowed us to progress significantly in terms of understanding how proteins are sequenced
and how errors in sequencing can impact an individual’s health. The Human Genome Project has also projected the
biological sciences significantly further in understanding the human body and genetic conditions. Briefly, discuss how
proteins might undergo a sequencing error and how that might impact one of the protein functions.
Answer: Proteins are sequenced through a process that is quite complex, but is described in this chapter as a two-step
process: transcription and translation.
A portion of DNA is needed to make a template for the mRNA (messenger RNA), which will transport the template code
to the RNA on the ribosomes. In this first sequence the DNA lines up with the mRNA, the mRNA coding with the exact
sequence of the DNA. This process is called transcription of the template of DNA. The genetic code is being transcribed
onto the template of mRNA. The mRNA dissociates with the DNA after it acquires the sequence and takes the sequence
to the ribosomes in the cell cytoplasm, where synthesis of the protein occurs with help from the tRNA. The tRNA acquire
amino acids from the materials around the cell and in the body fluids. The tRNA then usher the amino acids into position
to form the correct primary protein structure. This process is called translation in that the mRNA is translating to the
tRNA the genetic code for the protein. Once the protein is completed, it is attached to its appropriate component, may
undergo further processing, and moves on to assume its function.
Every protein is made for a very separate and different function and if, in the course of transcription, mRNA transcribes
even one different amino acid, the protein may function poorly or not at all. Your text describes the misplacement of a
valine in the position of a glutamic acid in the case of hemoglobin, which drastically alters the hemoglobin, resulting in
sickle cell anemia. While your body carries out the process an amazing number of times a day, seldom does it error in its
mission. Yet, on occasion, there are protein sequencing errors that can be problematic to fatal—and due to only one amino
acid. It is the Human Gemone Project’s work will allow scientists to further study these sequencing errors, predict them,
and counsel and advise clients. The science of nutrition is on the verge of many new discoveries as well as challenges.
6.
The Human Genome Project is forging the way for many scientists, including the nutrition science field. Discuss some of
the pros and cons of this project for clients and professionals in the nutrition field.
Answer: Students are being asked to use not only the information in the text to answer this question but also to develop a
heightened understanding for how clients as well as professionals might react to the changing paradigms that form
nutrition education programs with the Human Genome Project. As science advances, some clients and health care
professionals remain steadfast or tried and true to the “don’t change what is not broken” theory while others are anxious to
try new things and forge new frontiers. The risks in this approach can be great indeed for both the client and the
professional, yet the payoff may be worth it. As a professional, the obligation to maintain standards of professional
licensure, practice based on solid scientific evidence, and guide the client accordingly must be carefully followed, despite
unique therapies the client might try. Therefore, in this question, the student must think about the advantages and
disadvantages of gene profiling and consider where clients might believe there are great opportunities and great risks to
their health. Professionals must weigh advances they may provide for the client and decide when the client is better off
following a traditional therapy.
Pros for Client: With the sequencing of the human genome, the potential to identify genetic predispositions to any variety
of illnesses is advanced. Many scientists and medical professionals predict that with this possibility, clients will be
provided with advance information as to potential medical issues and therefore these same clients can alter their lifestyle
and health habits accordingly. Nutrition and dietary habits would be a primary area in which to seek improvements to
prevent and/or reduce one’s risk for diseases of any sort. For example, if an individual is notified through their genetic
profile that they have a gene for diabetes, this individual would pursue regular medical care, blood sugar monitoring, a
diabetic nutrition program, etc. If the individual were to pursue such a program with care, he or she might be able to avoid
becoming diabetic, minimize some of the complications of diabetes, or reduce the number of medications needed to
control diabetes, given a strict program of medical and lifestyle interventions.
Outcomes from the Human Genome Project will allow clients to approach and plan their health, medical care, and
lifestyle habits differently. In addition, the information can help clients planning to have children understand what types
of genetic risks the fetus may have and make their family planning decisions based on such information. Again, in some
cases, nutrition and nutrition education could be a vital part of improving the outcome or enhancing the outcome for these
clients.
Data from the Human Genome Project will, over time, allow scientists to develop more effective treatments for clients
with medical and nutritional illnesses and hopefully also work to advance a cure for illnesses. For instance, with the many
types of cancer, the potential to understand the mutation and develop a treatment is conceivable.
Genetic counselors work with clients who have family histories of inherited genetic disorders or fear the possibility of
having a child with a genetic disorder and use the data available to them through blood samples and family profiles to
assist a couple who is beginning to plan a family. Through their work, a couple can better understand their risks and the
potential risks to the unborn fetus (for a genetic disorder) prior to trying to conceive. Should the genetic counselor have
information that dictates that a couple will most definitely produce a child with a genetic defect, the couple can then
decide if they want to avoid pregnancy or initiate it knowing the outcome. They are then informed consumers and can
prepare accordingly for the child, should they choose to have one.
Food Production: While there are already many examples of genetic engineering in the area of agriculture, the Human
Genome Project does open the possibility for many new areas. Given that we are already capable of producing babies and
animals in test tubes, clearly the possibilities to develop, grow, and invent many types of food products are endless.
The goal in genetic engineering of fruits and vegetables and/or food products is to be able to develop and produce a
“better” product by manipulating the genetic profile with the best profile possible and then producing the items in the best
environment possible.
Cons for Client: While the Human Genome Project does have the potential to provide enormous volumes of information
to any particular client, the overload of information and the technical detail of this information alone could be very
overwhelming to some consumers. In addition, a consumer’s ability to fully understand such information is quite variable
and does truly impact the outcome of successful nutrition education programs. How much information any one person
needs and understands will be variable as will how much any one person will want this information. How will standards
be set for the information provided? Also, who will be able to have access to the information? If individuals have genetic
predispositions to diabetes or cancer and the information can be accessed by insurance companies, will these same
individuals be denied access to health insurance (assuming the same health insurance system)?
Genetic testing is an expensive undertaking. Who pays for this testing? Is it required or optional? If the individuals find
out that they have a genetic profile for a particular illness, how can a system be developed to optimize the chances that
that particular client will follow the medical, nutritional, and lifestyle regime that is required to minimize the health care
costs? Who would be responsible for oversight of that system? Should clients be required to follow any particular regime
if they are genetically profiled for a particular disease? Should they be denied medical care if they do not follow their
prescribed program?
While the information from a genetic profile could be quite helpful to an individual, some individuals may not want to be
informed in advance of such information. Some individuals would “rather take their chances” and live life as it is played
out. Critics of genetic counseling believe that it takes the spontaneity out of living and in some cases places the individual
in a mode of “waiting for the other shoe to drop.” These individuals see having such information as a burden rather than a
window of opportunity. Others believe that information from the Human Genome Project that is used to predict illness
and better understand the health status of an individual is somewhat like “playing God,” as one may base their entire life
on genetic data to the point of not really living. A person might be so focused and fearful of the genetic information that
s/he adheres to a rigid lifestyle of exercise, nutrient-rich foods, and frequent medical testing, yet dies from a car accident,
never suffering any issues from the purported genetic illness.
Critics of genetic engineering believe that produce and food products that are a result of genetic engineering may not be
exactly the same as those produced by nature, thus adding another unknown potential toxin into the food supply. In these
cases it is a wait and see situation, as any new element added to the food supply might take approximately 20 years to
demonstrate any potential negative outcome in humans or in the environment. Therefore, there are a few more years to
wait before the final verdict is in on genetic engineering of products, etc.
Pros for Nutritional Professional: The Human Genome Project has great potential for the nutrition field. First, the science
of nutrition is actually quite young when compared to other sciences such as chemistry, physics, and biology. While much
is known, so much more is still to be discovered. Through the Human Genome Project, the science and discoveries in
nutrition are poised to be expanded. Second, in knowing of potential genetic mutations in humans, we learn how to treat
and perhaps cure these diseases and we assist clients in pursuing medical care and lifestyles that support enhanced health.
Certainly nutrition is primary to the majority of chronic diseases that plague American citizens. This factor increases the
importance of nutrition, nutritional care, and nutrition education in health care and will increase the visibility of RDs as
part of the health care team.
To enjoy the opportunities, nutritional professionals must keep current in their knowledge of the advances in the Human
Genome Project and impacts to the profession. Readings in the professional literature as well as a firm understanding of
biochemistry and genetics will be essential to the growth of our profession. Expanded career opportunities will emerge
from the Human Genome Project in the field of nutrition science, not only broadening career opportunities for students
studying nutrition but also potential salary advances. Growth in collaborating with other health care professionals is
necessary now and will continue. Physicians and other health care providers will look to the nutrition professional (RD) to
work with clients on their diets in an effort to minimize or avoid any negative health consequence from a genetic
inheritance.
Given the advance knowledge of a potential illness, the RD can work with clients to fully realize better health and better
eating habits. Many individuals retain poor eating habits as a result of “denial” that they will be confronted with any
adverse health event. However, if the client is assured that they are genetically coded for any particular disease, this
knowledge can heighten their willingness to faithfully follow better nutritional habits. Given that nutritional habits are
often similar among family members, if one family member retains positive dietary habits, the changes are very good that
the remaining family members will also follow similar positive dietary habits. The potential for this type of trend
throughout the United States could potentially reduce obesity, cardiovascular disease, and many chronic diseases that are
a result of poor nutritional/dietary habits.
Genetic Engineering of Produce/Food Products: Mother Nature can be quite devastating with regard to crops, while
multiple issues can result from breeding poultry, beef, pork, etc. for the food supply. In addition, growing crops and
breeding animals take a great deal of land, space, and sometimes luck! Genetically engineering produce and other
products for the food supply can take many of the risk factors out of the equation as well as support the growth of a
genetically superior product. For example, instead of growing tomatoes on the land, there are now multiple processes for
growing tomatoes including growing them on water. Developments such as these allow growers to avoid the changing
nature of Mother Nature and control the growing environment.
In the case of poultry, beef, etc., breeders are able to control the genetics of the breed, enhancing the quality of the
product. Additionally, the breeding is reliably done instead of waiting for Mother Nature again, in the event that the
animals do not feel like breeding. The key here may also be the land that animals may require prior to slaughter. Cattle
require a significant amount of land to graze in order to grow, putting great demands on the capabilities of the land to feed
the population of the U.S. Genetic engineering has the potential to provide answers to some of these truly significant
environmental dilemmas in the U.S.
Genetic engineering also has the potential to provide consumers with new, flavorful, and healthful food products not
formerly available through their innovation and creation. Consumers look for new food products that “break neither the
bank nor the waistline” and science may provide some of those answers. Food manufacturers work hard to provide
consumers with options. Though they are not genetically engineered, products such as the fat replacers and alternative
sweeteners are examples of recently developed diet alternatives. It is important for the RD to stay current with all new
products as consumers will challenge the RD about them.
Cons for Nutritional Professional: Innovation is a wonderful thing but what happened to “leaving well enough alone and
living for today”? As noted with the consumer or client, even if genetic information is available to them to assist them in
making the most informed medical decision, the client may well want to be uninformed. And, as with the client, who then
becomes responsible for the number of issues that surround such decisions? While some clients may be more motivated to
follow strict dietary plans if they know that they are genetically prone to a heart attack, others may believe that there is
nothing that is going to stop it so why not “live for today”?
Nutrition education/counseling for a population that has available to them a massive amount of genetic information can be
complex without some standard guidelines. It will be important for the American Dietetic Association and RDs to prepare
policy guidelines for client counseling and education with genetic information. Should practitioners practice consistently
if clients want to experiment or should practitioners work with each individual client and their ability to understand the
information given to them and ability to use it? An excellent example would be the sports nutrition movement. The
American Dietetic Association’s position on supplementation at the beginning of significant endurance events where
athletes were seeking nutrition counseling was that it should not be encouraged. However, RDs that worked with
professional and world-class athletes knew that if they were to be taken seriously, they had to be open to vitamin and
ergogenic supplementation or the athlete would go elsewhere. Thanks to the science of sports nutrition, we now know that
endurance athletes do need a bit more protein to support tissue repair and that while some ergogenics still need much
more research, there is some evidence to support some of their use. Finally, the field advances every day, and those RDs
that took risks in the early days were at the forefront of this new field.