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BIO AVAIL ABILITY

BIO AVAIL ABILITY. (what we get from what we have taken in). BIOAVAILABILITY. Definition What makes it up Critical phase Hormonal factors in How its measured Membrane transporters Special cases for redox metals. First basic law of nutrition :

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BIO AVAIL ABILITY

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  1. BIOAVAILABILITY (what we get from what we have taken in)

  2. BIOAVAILABILITY Definition What makes it up Critical phase Hormonal factors in How its measured Membrane transporters Special cases for redox metals

  3. First basic law of nutrition: No nutrient is absorbed and utilized to the full extent that it is fed Steven Blezinger

  4. Define Bioavailability • That which becomes bioavailable • The fraction (or percentage) of nutrient absorbed that is useful to the body • The degree to which an absorbed nutrient is available to the system

  5. Nutritional Definition Bioavailability is a post-absorption assessment of how much of a nutrient that has been absorbed becomes functional to the system

  6. Food Science Definition Bioavailability is a assessment of how much of a nutrient is retained in the food product after processing for the consumer

  7. Bioavailability in toto Raw Food Product (100%) Total (proximate analysis) Processed Food Chemically available Digestion Absorption Biologically available Cellular uptake Functional mineral

  8. Basic Scheme of Proximate Analysis Air dried Sample (oven) Water free sample Extract with ether Extract Boil in acid Residue (ignite) Filtrate Residue Fat Ash Nitrogen free extract Boil in alkali Residue (crude fiber) ignite Ash Nitrogen (Total N content)

  9. Biological Availability (Bioavailability) Definition can be based on either the percentage of a nutrient ingested or the percentage of a nutrient absorbed that becomes useful to the organism The percentage ingested is preferred by some because the percentage absorbed is difficult to determine and relies on an indirect analysis The percentage absorbed is, nonetheless, a more accurate appraisal of bioavailability

  10. The fraction of the total amount absorbed that performs a function Digestion Absorption Blood Transport Which is the most critical phase for minerals? Liver and kidney excretion Losses along the way Membrane transport Intracellular movement Functional Site

  11. Recall A nutrient is considered outside the body until it passes thru the intestinal barrier

  12. The amount that gets absorbed depends on: Digestibility of the food source Solubility of the mineral Extrinsic Factors Elements in the food source that hinder or facilitate absorption With a focus on the organism, bioavailability depends on: Age Health Nutritional state Physiological state Genetic predisposition Gender Developmental stage Species Intrinsic Factors

  13. Components of Bioavailability • Digestion • Absorption • Liver surveillance • Transport • Transmembrane movement • Intracellular movement • Target binding Absorptive Phase Assimilation Phase

  14. Why Not Absorption Alone as an index of Bioavailability As pointed out by O’Dell, assimilation may be a major part of a mineral’s bioavailability and needs to be assessed separately Absorption % Retention %a 75Se as selenite 92 <50 75Se as selenomethionine 96 >80 aArbitrary units 2-picolinic acid enhances zinc absorption in rats by nearly 60%. But, also increases zinc excretion so there is no net effect on retention and hence no increase in bioavailability

  15. Assessing bioavailability by the slope ratio method Assessing Phytate (in soy flour) as a factor in Zinc bioavailability Zn carbonate Zn Beef Beef/carbonate = 0.97 Body wt of 3 wk old chicks Soy/carbonate = 0.31 Zn Soy flour 4 6 8 10 14 Zn in the diet (mg/kg)

  16. Quantifying Bioavailability % Bioavailable = % absorbed x % assimilated x 10-2 If a diet contained 5 mg of a metal ion and 42% of the 10% absorbed was retained in the system, the % bioavailable would be ___________ which means ________ mg was rendered functional 420 2.1 0.21 42 0.42 4.2 .021

  17. Solution 5 mg 4.5 mg (90%) stays in lumen Intestine 0.5 mg absorbed (10%) % BA = %Abs x %Fun x 10-2 = 10 x 42 x 10-2 Functional site = 4.2 or 0.21 mg of the 5 mg taken in the diet 0.21 mg (42%) of absorbed becomes functional 0.29 (58%) of absorbed is non-functional

  18. Exam 1 An Overall Assessment of Minerals • What they are (chemistry) • What they do (biochemistry) • How they get in our body (absorption) • How they get into cells (transport, assimilation) • How efficient are they (bioavailability) • How are they regulated

  19. Chemistry • Chemical properties relative to function • Ionization • Solubility • Valence • Electronic configuration Biochemistry • Biochemical properties relative to function • Macro vs microminerals • Enzyme cofactors • Pathway components • Crystallization • Binding proteins Absorption • Solubility • Mucins, ligands, pH • Valence • Transport proteins (intestinal sites) • Cytosolic transport and storage • Export factors

  20. Transport and Assimilation • Transport proteins in plasma • Membrane receptors and channels • Membrane transport • Simple diffusion • Mediated diffusion • Active transport • Receptor mediated endocytosis • Cytosolic transport • Vesicles • Metallochaperones Regulation • Regulation of iron absorprtion • Iron control of ferritin and transferrin receptor (IRPs) • Hemochomatosis factors hepcidin and HFE • Regulation of calcium absorption • Control of calbindin and CaT1 by dihydroxy-vitamin D3 Bioavailability 1. Ways to measure mineral bioavailability

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