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Nutrition Lecture 5
Proteins and Health
1. Describe the chemistry, digestion and absorption of proteins from our diet.
Biochemistry Review (??)
2. Summarize the difference b/w dietary essential and dietary nonessential amino
acids.
 Types:
 Indispensable: Essential AA. Body can’t synthesize and have to get it
from dietary source. Limitation of 1 AA can affect the health.
 Dispensable: Nonessential AA. Body can synthesize these AA in
adequate amounts.
 Arginine, HMB (a metabolite of Leucine) and Glutamine increase wound repair in
patients.
3. Describe the special category of conditionally indispensable amino acids.
 Conditionally Essential AA: Conditionally Indispensable. During certain stressful
circumstances or conditions some of the non-essential AAs become essential.
 Cysteine and Tyrosine: Can be made from methionine and phenylalanine
respectively. However, if all four amino acids are limited in the diet, cysteine and
tyrosine become conditionally indispensable.
 Arginine and Glutamine: Are needed in very high amounts during trauma and
critical illnesses like infection. The body cannot make enough to meet the needs of
these amino acids during these situations. It’s become important that these amino
acids are provided in diet in these conditions b/c they are used for immune and GI
function.
4. Explain the concept of a limiting amino acid using the concept of protein quality.
 Food protein provides a mixture of essential and non-essential amino acids, which
are used to synthesize proteins for maintenance and functioning of the body. If the
diet is deficient in one or more of the essential amino acids, the body will break
down its tissues, like muscle, to meet its amino acid needs. If dietary protein is not
provided, the rate of protein synthesis will gradually slow down and protein
breakdown will exceed protein synthesis. Such a situation can lead to poor state of
health, making the body vulnerable to infection and lethargy.
 The protein quality of food protein depends on its digestibility and its ability to
provide all essential amino acids.
5. Describe why the Protein Digestibility Corrected Amino Acid Score (PDCAAS) is
superior to other methods for evaluating the protein quality of food proteins.
PDCAAS is superior to other methods for evaluating the quality of food proteins. It has
replaced the Protein Evaluation Ratio (PER). It measures the quality of a protein in food
based on the amino acid requirements of the human in its appropriate age group, adjusted
for digestibility. The highest PDCAAS value that any protein can achieve is 1.0. This score
means that after digestion of the food protein, it provides per unit of protein, 100 % or more
of the indispensable amino acids required by the two to five year old child. Any amino acids
in excess of those required to build and repair tissue would not be used for protein synthesis,
but would be catabolized and eliminated from the body or stored as fat. Two reasons for
adopting PDCAAS over PER by FDA: 1) PDCAAS is based on human amino acid
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requirement which is better than method based on animal amino acid requirement. 2)
FAO/WHO had recommended PDCAAS for regulatory purposes and FAO/WHO is a
recognized international organization that is experienced in establishing theses types of
standards.
6. Describe problems that are associated with deficient dietary protein intake.
(Marasmus, Kwashiorkor and Refeeding syndrome)
 Clinical Sings of Protein Deficiency:
 Hair loss
 Easily pluckable hair
 Muscle wasting
 Pressure sores
 Delayed wound healing
 Kwashiorkor:
 Develops where there is severe protein deficiency
 Seen in children living in developing nations.
 When dietary protein is deficient, the body is forced to prioritize its
protein needs. As a result, the synthesis of the most vital body proteins
takes precedence over the synthesis of proteins of lesser importance.
This is seen in the deterioration of skin and hair w/ the changing of their
color and texture, a fluid imbalance due to reduced synthesis of blood
proteins lead to the development of edema, apathy and listlessness, failure
to grow and gain weight, poor immune status and increased susceptibility
to many diseases.
 If treated w/ replenishment of nutrients then recovery is possible but if
not treated it can lead to death b/c of infections.
 Marasmus:
 Results from chronic lack of energy in the diet
 Body protein is diverted from its role in growth and maintenance to be
used as a source of energy
 Apathy and/or failure to grow and gain weight is seen
 Unlike kwashiorkor where some subcutaneous fat is still present due to
receiving energy, people w/ marasmus have little or no subcutaneous fat
 Susceptible to disease
 Diminished brain function if marasmus occurs during the stages of brain
development and not treated.
 Refeeding Syndrome:
 Refeeding syndrome occurs when previously malnourished patients are
fed w/ high carbohydrates loads, the result is a rapid fall in phosphate,
magnesium and potassium, along w/ an increasing ECF volume, leading
to a variety of complications.
 Complications include increased cardiac workload, heart rate, oxygen
consumption, acute heart failure in pt. w/ cardiovascular disease,
increased CO2 and decreased O2, dyspnea, tachypnea, nausea and
diarrhea etc.
 Decreased phosphorous level can cause complications: Respiratory
failure, cardiac failure, cardiac arrhythmias, rhabdomyolysis, seizures,
coma red cell and leucocyte dysfunction.
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7. Explain how serum protein levels can be used to determine a patient’s overall
nutritional status and describe limitations that must be considered. (Serum proteins
used in nutritional assessment include albumin, transferring, prealbumin and retinol
binding protein)
When there is protein deficiency the protein serum levels are altered due to reduced protein
formation and so serum protein levels can be used to determine a patient’s overall nutritional
status.
 Albumin: Measurement of serum albumin is easy and inexpensive so it’s widely used
in nutritional assessment. The limitation does exist. If there is coexisting sepsis or
stress then nutritional support won’t change the albumin level but if there is no
sepsis or stress of any kind present along w/ nutritional deficiency then refeeding
would show albumin level change. However, serum half life of albumin is 18 to 20
days; it takes about 2 wks to see improvement in serum albumin level w/ nutritional
repletion.
 Serum Transferrin: Serum transferrin has a half life of 7 to 10 days, so theoretically
better than albumin as a nutritional marker. However, serum transferrin levels also
respond to iron status. They go high in iron deficiency and so if there is coexisting
iron deficiency along w/ protein malnutrition then the serum transferrin level may
be high instead. So that is the limitation associated w/ serum transferrin.
 Prealbumin: Functions as thyroxin transport and as a carrier for retinol-binding
protein. (??) Its serum half life is 2 to 3 days and so measurable changes in
prealbumin levels occur in 1 wk of a change in nutrient intake. The limitation w/
prealbumin is that there is increase level of prealbumin in renal failure and also
prealbumin level can vary unpredictably w/ the carbohydrate content of the diet and
during metabolic stress.
 Retinol Binding Protein: Blood protein w/ half life of 12 hours and is the most
sensitive to mild depletion or repletion of body protein (mal malnutrition)
8. What is the most effective way to treat refeeding syndrome?
Don’t Know??
9. What kind of malnutrition does the patient have and what is the evidence for it?
(Case Study Question 1 on page 9)
Marasmus (??)
10. What is the nutritional impact of CAPD (Chronic Ambulatory Peritoneal Dialysis)?
Don’t Know ??