Lecture 16: Protein-AA Requirements

Question 1

How is the requirement for dietary protein determined?

Answer 1

amount need to replace what is lost

Question 2

How much of protein is made up of nitrogen?

Answer 2

Protein is 16% nitrogen and protein weighs 6.25 x that of nitrogen so use N x 6.25 as protein equivalent. (mg to g conversion)

Question 3

EAR for protein

Answer 3

0.66 g/kg/day for M/F 19+

Question 4

Protein RDA for healthy adult M/F

Answer 4

0.8 g/kg/d

Question 5

What factors effect DRI?

Answer 5

• age
• body size (LBM)
• physiological state
• E intake

Question 6

Who requires higher protein intake?

Answer 6

• children - growth
• pregnancy - tissue expansion and fetal growth
• lactation - N in human milk

Question 7

AMDR for protein

Answer 7

10-35% of total E intake

Question 8

good vs. bad sources of protein

Answer 8

Question 9

What is an important factor affecting protein utilization?

Answer 9

carbohydrates and fat intake because when energy is insufficient, amino acids will be used for fuel rather than protein synthesis (↓insulin) so more protein degradation and urea

Question 10

What happens to amino acids when oxidized as fuel?

Answer 10

mostof their carbon enters the TCA cycle and other central pathways of fuel metabolism via pyruvate, oxaloacetate, alpha ketoglutarate or acetyl CoA.

Question 11

protein status with inadequate intake

Answer 11

• ↓protein synthesis with inadequate intake
• body will utilize what protein you have with inadequate E intake
• Acute protein deficiency
• chronic deficiency

Question 12

acute vs. chronic deficiency of protein

Answer 12

• acute: greatest effect on cells with rapid turnover; rare not clinically important
• chronic: affects all organs, especially functions of immune system, small intestine (mass, gut mucosa function & permeability) & kidneys; harmful effects on brain function for infants and children

Question 13

What is protein nutrional status evaluated by?

Answer 13

• plasma proteins such as albumin and transferrin
• Assessmnet of rapidly growing tissues such as skin and hair
• LBM: loss occurs over longer term

Question 14

Indications of protein deficiency in infants/ children

Answer 14

• borderline inadequate protein intake results in failure to grow (length or height)
• increased infections
• mid- upper-arm muscle circumference/ diameter used as indicator (less affected by edema)

Question 15

Diseases of protein malnutrition

Answer 15

• Marasmus
• Kwashiorkor

Question 16

Marasmus protein malnutrition

Answer 16

energy + protein deficiency
* Muscle wasting, subcutaneous fat loss, growth retardation
* Diet lacking in calories & protein likely also lacking in micronutrients & essential fatty acids

Question 17

Kwashiorkor protein malnutrition

Answer 17

adequate energy but protein deficiency so dont have synthesis of the machinary to actually do anything
* Growth retardation, edema, swollen abdomen, fatty liver, skin & hair changes, anemia, diarrhea
* also causes ↓ synthesis of enzymes for lipid transport, hypoalbuminemia

Question 18

kwashiorkor in developing vs. developed countries

Answer 18

• Developing countries: Associated with poverty, appears after breast- feeding discontinued (~12 mos of age)
• Developed countries: Severely burned, trauma or sepsis patients, chronic malabsorptive conditions… rare cases of nutritional ignorance, food faddism, or food allergen avoidance (in infants)

Question 19

Marasmus vs. kwashiorkor

Answer 19

Kwashiorkor children have higher mortality rate than Marasmus

Question 20

What does hypoalbuminemia lead to?

Answer 20

defects in body fluid homoeostasis and edema, and deficiencies in apoB-lipoprotein synthesis to a fatty liver

Question 21

Protein intake in north america

Answer 21

in general consume excess energy + protein from many protein sources: bread, milk, meat, soy so low risk for protein or AA inadequacy

Question 22

low end and high end of protein intake in north america

Answer 22

elderly women: ~27 g
young men: 190 g

Question 23

What is high protein intake a result of?

Answer 23

• ↑ in overall E intake
• ↓in CHO &/or fat

Question 24

Groups that commonly consume high amounts of protein

Answer 24

• weight lifters and body builders (up to 3g/kg/d)
• some tribes (>30% E intake) - mainly hunters

Question 25

What is protein reccomendation intake for athletes?

Answer 25

> 1.2-1.8 g/kg/d

Question 26

Cautions with high protein diets

Answer 26

• Short term: weight loss, calcium loss, ketoacidosis
• ‘rabbit starvation’
• Adverse effects in patients with renal failure because they have to filtrate a lot of urea

Question 27

Essential AA requirements

Answer 27

Dietary protein is required to supply N for synthesis of dispensible AAs, but also needs to supply indispensable AAs
* best to consume combination of proteins to ensure you get all you need
* AA needs (per bw) decrease with age

Question 28

Protein quality

Answer 28

Different protein sources have various amino acid compositions and need to evaluate the ability of particular proteins or mixtures of proteins to meet the AA requirements of the body

Question 29

What are the components of protein quality?

Answer 29

• AA pattern or score
• digestibilty (food matrix considerations)
• hydrolysis
• chemical integrity effecting availability of AAs (heat damage)

Question 30

What is compared with protein digestibility?

Answer 30

True digestibility (Dt) vs apparent digestibility (Da)
* Da is the fraction of amino acid intake that is absorbed (= (intake - fecal exctretion) / intake)
* Dt is Da corrected for endogenous protein losses therfore Da < Dt

Question 31

What does protein digestibility depend on?

Answer 31

source and other foods ingested

Question 32

digestibility of animal vs. plant protein

Answer 32

• Animal protein has high digestibility (>90%)
• Plant protein has relatively low digestibility (70-90%)

Question 33

What is the golden standard for protein source of Dt?

Answer 33

cooked egg Dt is about 97% which is the highest so most AA from eggs is absorbed and circulated

Question 34

What might lower digestibilty of plant protein sources?

Answer 34

• Some protein may be encapsulated in cell wall (matrix) such as fibre and cannot digest \ cannot access the protein
• trypsin inhibitors (legumes, cereals, raw egg white)

Question 35

What factors can effect the chemical integrity of proteins?

Answer 35

• Food processing and storage (at high ambient temperatures) may affect aa bioavailability.
• Heat can induce irreversible modifications on lysine residues thus reducing digestibility.
• Treatment with strong acids.
• Ultrastructural changes in amino acids can make them metabolically unavailable even if they are absorbed.

Question 36

What is the major factor determining protein quality?

Answer 36

amino acid pattern
* Ideal protein will have the right amount of essential and non- essential AAs
* the limiting AA is the most deficient essential amino acid in the protein relative to requirement