Lecture 16: Protein-AA Requirements Flashcards
How is the requirement for dietary protein determined?
amount need to replace what is lost
How much of protein is made up of nitrogen?
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)
EAR for protein
0.66 g/kg/day for M/F 19+
Protein RDA for healthy adult M/F
0.8 g/kg/d
What factors effect DRI?
- age
- body size (LBM)
- physiological state
- E intake
Who requires higher protein intake?
- children - growth
- pregnancy - tissue expansion and fetal growth
- lactation - N in human milk
AMDR for protein
10-35% of total E intake
good vs. bad sources of protein
What is an important factor affecting protein utilization?
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
What happens to amino acids when oxidized as fuel?
mostof their carbon enters the TCA cycle and other central pathways of fuel metabolism via pyruvate, oxaloacetate, alpha ketoglutarate or acetyl CoA.
protein status with inadequate intake
- ↓protein synthesis with inadequate intake
- body will utilize what protein you have with inadequate E intake
- Acute protein deficiency
- chronic deficiency
acute vs. chronic deficiency of protein
- 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
What is protein nutrional status evaluated by?
- plasma proteins such as albumin and transferrin
- Assessmnet of rapidly growing tissues such as skin and hair
- LBM: loss occurs over longer term
Indications of protein deficiency in infants/ children
- 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)
Diseases of protein malnutrition
- Marasmus
- Kwashiorkor
Marasmus protein malnutrition
energy + protein deficiency
* Muscle wasting, subcutaneous fat loss, growth retardation
* Diet lacking in calories & protein likely also lacking in micronutrients & essential fatty acids
Kwashiorkor protein malnutrition
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
kwashiorkor in developing vs. developed countries
- 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)
Marasmus vs. kwashiorkor
Kwashiorkor children have higher mortality rate than Marasmus
What does hypoalbuminemia lead to?
defects in body fluid homoeostasis and edema, and deficiencies in apoB-lipoprotein synthesis to a fatty liver
Protein intake in north america
in general consume excess energy + protein from many protein sources: bread, milk, meat, soy so low risk for protein or AA inadequacy
low end and high end of protein intake in north america
elderly women: ~27 g
young men: 190 g
What is high protein intake a result of?
- ↑ in overall E intake
- ↓in CHO &/or fat
Groups that commonly consume high amounts of protein
- weight lifters and body builders (up to 3g/kg/d)
- some tribes (>30% E intake) - mainly hunters
What is protein reccomendation intake for athletes?
> 1.2-1.8 g/kg/d
Cautions with high protein diets
- 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
Essential AA requirements
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
Protein quality
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
What are the components of protein quality?
- AA pattern or score
- digestibilty (food matrix considerations)
- hydrolysis
- chemical integrity effecting availability of AAs (heat damage)
What is compared with protein digestibility?
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
What does protein digestibility depend on?
source and other foods ingested
digestibility of animal vs. plant protein
- Animal protein has high digestibility (>90%)
- Plant protein has relatively low digestibility (70-90%)
What is the golden standard for protein source of Dt?
cooked egg Dt is about 97% which is the highest so most AA from eggs is absorbed and circulated
What might lower digestibilty of plant protein sources?
- 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)
What factors can effect the chemical integrity of proteins?
- 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.
What is the major factor determining protein quality?
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
