NBA1 (molecular aspects of) protein digestion and absorption

17 important questions on NBA1 (molecular aspects of) protein digestion and absorption

Are there alternative pathways for protein absorption?

Infants
  • transcytosis of larger peptides

Increase intestinal permeability
  • Paracellular transport
  • Epithelial integrity
  • Exercise

Large peptides; incl. Allergens


image is a study that they have done --> with exercise the peak of peanut allergie was higher....? Exercise has a negative impact on the intestinal impermeability

Protein quality; how many are essential and how many are nonessential?

Centers around 20 AA
  • Nonessential AA - 11
  • Essential AA - 9
    • conditionally essential AA (synthesised in limited amounts; diet in case status of rapid protein synthesis [e.g. Growth])

What is the definition of protein quality? And what is its relevance?

  • Nutritive value of a protein depends on its capacity to provide nitrogen and amino acids in adequate amounts to meet the requirements of an organism
  • relevance
    • growing population
    • specific groups
      • children
      • disease
      • elderly
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Protein quality is dependent on...

  • AA composition
  • AA bioavailability


nutritive value of a protein depend on its capacity to provide nitrogen and amino acids in adequate amounts to meet the requirements of an organism

By what is the amino acid bioavailability influenced?

  • Digestibility
    • net absorption of an amino acid
  • Chemical integrity
    • the proportion of the amino acid that, if absorbed, is in a utilisable form (e.g., bioavailable/reactive lysine)

Name the scoring system for the evaluation of protein quality and what the formula is.

DIAAS: digestible indispensable amino acid score
  • recommended in 2011 by FAO
  • DIAAS% = 100 x lowest value [(mg of digestible dietary indispensable amino acid in 1g of the dietary protein)/(mg of the same dietary indispensable amino acid in 1g of the reference protein)]


in 1989 the PDCAAS [protein digestibility corrected amino acid score] was recommended. Sinds 2011 the DIAAS

What are the improvements & limitations of the DIAAS

  • Digestibility at ileal level, not faecal
    • determined in human > growing pig > growing rat
  • Measurement bioavailable lysine (no Maillard products)
  • AA pattern of reference protein
    • age-groups (birth-6; 6m-3y;>3y)
  • no truncation at 100%
    • except sole food source or already mixed diet

  • Limitation
    • still one score per protein --> AA individual nutrients

In which 3 ways can the digestibility be measured in humans?

  • Naso-ileal intubation
    • liquids, powders, non-fibrous food
  • Ileostomates
    • fibrous, coarse food
  • Less-invasice techniques
    • isotope methods

Ileostomates -- Proteos study =

Protocol
  • 'healthy' subjects
  • breakfast with protein or protein-free meal
  • collection of digest - 9 hours

Considerations
  • not completely healthy
  • microbiota ileum
  • total collection & marker recovery

What is the principle dual isotope approach?

  • Intrinsically labelled test protein
  • different labelled standard protein/free AA
    • known digestibility
  • postprandial ratio of appearance of differently labelled amino acids --> evaluation absorption of test protein


--> less invasive: useful to determine digestibility in children, elderly, patients

Dual tracer approach - 15N & 2H

Image




  • Cystic fibrosis patients
  • Quantify protein maldigestion - Pancreatic enzyme

Dual tracer approach - 2H & 13C

Digestibility of spirulina (13C)
  • relative to free amino acids

Digestibility of legumes, eggs, meat, rice (2H)
  • relative to spiruline

What is the protein origin [digestibility]

  • Dietary protein
  • Endogenous protein
    • Basal; depends on quantity of intake, independent of diet
    • Specific; depends on diet
      • fiber (type and concentration)
      • anti-nutritional factors

What is the apparent vs true digestibility?

  • Difference in correction for endogenous losses

Apparent:
  • Digestibility(%) = (ingested - digestive losses) / ingested x 100

True:
  • Digestibility(%) = (ingested - (digestive losses - endogenous losses)) / ingested x 100

What are the methods to determine endogenous losses?

  • Protein - free diet
    • basal endogenous losses
  • labelled protein sources
    • 15N labelled protein source
    • total endogenous losses --> 'real' digestibility
    • recycling
  • hydrolysed proteins with ultrafiltration of digesta

Age & protein digestibility

No complete consensus on decreased digestive and absorptive function in elderly
  • rats: 5 weeks or 20 months
  • true faecal protein digestibility
  • results
    • low differences for properly processed protein products
    • larger differences for proteins products with anti-nutritional factors

Scoring protein quality - calculation
[example for a single food ingredient - milk powder]

  • (mg of digestible dietary indispensable amino acid in 1 g of the dietary protein)
  • lowest value


13 * 0.9 = 12

12/17= 0,69

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