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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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Bioavailability

BIOAVAILABILITY

(what we get from what we have taken in)


Bioavailability

BIOAVAILABILITY

Definition

What makes it up

Critical phase

Hormonal factors in

How its measured

Membrane transporters

Special cases for redox metals


Bioavailability

First basic law of nutrition:

No nutrient is absorbed and utilized to the full extent that it is fed

Steven Blezinger


Define bioavailability

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


Bioavailability

Nutritional Definition

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


Bioavailability

Food Science Definition

Bioavailability is a assessment of how much of a nutrient is retained in the food product after processing for the consumer


Bioavailability

Bioavailability in toto

Raw Food Product (100%)

Total (proximate analysis)

Processed Food

Chemically available

Digestion

Absorption

Biologically available

Cellular uptake

Functional mineral


Bioavailability

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)


Bioavailability

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


Bioavailability

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


Bioavailability

Recall

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


Bioavailability

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


Components of bioavailability

Components of Bioavailability

  • Digestion

  • Absorption

  • Liver surveillance

  • Transport

  • Transmembrane movement

  • Intracellular movement

  • Target binding

Absorptive Phase

Assimilation Phase


Bioavailability

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


Bioavailability

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)


Bioavailability

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


Bioavailability

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


Exam 1

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


Bioavailability

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


Bioavailability

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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