Nutrition Topic 4
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What are the 3 classifications of AA?
Indispensable, conditionally indispensable, dispensable
How is metabolic flux of amino acids determined?
By following 'tracers'
What is a nutritionally indispensable AA?
Cannot be synthesized by the animal organism out of materials ordinarily available to the cells at a speed commensurate with the demands for normal growth
Why are amino acids needed?
- Nitrogen Balance
- Plasma AA response
- Direct AA oxidation
- Indicator AA oxidation
- 24h balance
- or measure of organ or system function
What are the general aspects of experimental approaches for nitrogen analysis?
- All methods should give the same answer
- Subjects should be studied at >6 test AA intake levels above and below requirement
- Endpoint should show a clear response to change in test AA intake
- Question of adaptation to test AA intake
What is indicator AA oxidation (IAAO)?
- When an indispensable AA is limiting, then all other indispensable AA wil be oxidized (remember that AA cannot be stored)
- Increasing intake of limiting amino acid will decrease IAAO
What is the minimaly invasive IAAO model?
- Tracer administration: repeated oral 'nibbling' of tracer solution after 4h feed equilibration
- Sampling: Breath collection for CO2 enrichment, urine in place of blood for plasma AA enrichment
- Problem: D-AA are efficiently excreted in the urine
- D- and L- AA can be differentiated by GCMS (gas chromatography mass spectometry) using a 'chiral column'
Why is limiting AA important?
- Vegans with lower protein intake and lower protein quality- limiting AA is significant issue especially for children
- International- food security and diet diversity- very important especially for children
What is the function of histidine requirement?
- Histidine-free diet for 48 days, followed by repletion
- No effect on nitrogen balance
- Decreased protein turnover, phenelalanine oxidadation
What happens when people are fed 0.6g/kg/d for 7 days?
- Decrease in: protein turnover, albumin synthesis (negative acute phase protein), Glutathione synthesis (antioxidant capacity, increased sysceptibility to oxidative stress)
- Increase in: Fibrinogen synthesis (positive acute phase protein)
How are amino acids digested?
- Pepsin in stomach- acidic pH
- Proteases from pancreas in small intestine- luminal digestion
- Peptidases on brush border of intestinal epithelial cells
- Active transporters
How does the liver play into amino acid metabolism?
- Anabolic: constitutive protein synthesis, plasma protein synthesis, gluconeogenesis, lipogenesis
- Catabolic: amino acid catabolism, urea cycle
Synthesis of dispensible amino acids
- High flux rates
- High proportion from de novo synthesis
- Synthesis accounts for 8% of basal metabolic rate
- Ultimate precursor is gucose
- Ultimate precursor is glucose (except for tyrosine, for cysteine only the S is from methionine)
What are the issues in sulphur amino acid metabolism?
- Liver function
- Premature infants
- Intravenous feeding
How does glutathione relate to amino acid synthesis?
- Protection agains oxidative stress- conjuction with electrophiles, removeal of ROS
- Proteins, lipid membranes, DNA
- Immune system function
Does protein have an ergogenic effect?
- Probably power but not endurance
- Increased lean body mass: water, osmoregulation
- Genes in muscle upregulating myosin, cytoskeleton, protein and glycogen synthesis
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