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HUNT242 > Lecture 9: Intake vs. Amount Available to the Body > Flashcards

Lecture 9: Intake vs. Amount Available to the Body Flashcards

1
Q

What is bioavailability?

A

The proportion of a nutrient in a food that is digested, absorbed and utilised

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2
Q

What is the absorption of non-haem iron?

A

approx. 5-15%

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3
Q

How is iron in the body?

A

Through epithelial cells and fluids

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4
Q

How is iron lost in epithelial cells?

A
  • Skin (0.2mg)
  • Intestinal mucosal cells (0.1mg)
  • Urinary tract cells (0.1mg)
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5
Q

How is iron lost in fluids?

A
  • Blood (gut 0.4mg)
  • Menstruation
  • Bile (0.2mg)
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6
Q

What are the dietary requirements of iron?

A

Men: 8mg
Women: 18mg

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7
Q

What are the average iron losses per day?

A

Men: 1mg
Women: 2mg

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8
Q

What is bioavailability influenced by?

A
  • Chemical form
  • Composition of food and meal
  • Nutrient status
  • Physiological status
  • Amount consumed
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9
Q

What happens when someone has low iron stores?

A

Increased Fe absorption

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10
Q

What happens to iron absorption when someone is pregnant?

A

It increases

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11
Q

Why do we measure bioavailability?

A
  • NRV’s are set using %absorption
  • Identify & quantify new enhancers and inhibitors
  • Compare efficiency of new supplements
  • Develop algorithms to estimate absorption
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12
Q

What are isotopes?

A

Atoms with the same number of protons but different number of neutrons - similar chemistry different mass

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13
Q

What are the three components of an atom?

A
  • Protons (+)
  • Neutrons (0)
  • Electrons (-)
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14
Q

What are isotopes of Fe?

A

Fe-55, Fe-59, Fe-54, Fe-56, Fe-57, Fe-58

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15
Q

What are radioisotopes?

A

Atoms with an unstable nucleus that emit radioactive decay

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16
Q

What are the three types of radioactive decay (ionising radiation)?

A
  • Alpha particles
  • Beta particles
  • Gamma rays
17
Q

How does ionising radiation work?

A
  • Remove electrons from atoms and products damage tissues
  • Risk depends on route, dose, and ionisation energy
18
Q

What are the characteristics of alpha particles?

A
  • Low penetrating power
  • Cause high ionisation power
19
Q

What are the characteristics of beta particles?

A
  • More penetrating than alpha
  • Not as ionising as alpha
20
Q

What are the characteristics of gamma particles?

A
  • High penetrating power
  • Causes least ionisation
21
Q

What types of studies use radioisotopes?

A
  • Balance studies
  • Whole body counting
  • Plasma appearance
  • Hb incorporation
22
Q

What are the advantages of using radioisotopes?

A
  • True tracers
  • Often cheaper than stable isotopes
  • Minimal sample preparation needed
23
Q

What are the disadvantages of using radioisotopes?

A
  • Radiation dose
  • Cannot be used with pregnant or lactating women, infants or children
  • Ethical approval
24
Q

What are stable isotopes?

A
  • Stable nucleus so do not emit radiation
  • Naturally occuring
25
Q

What type of studies are stable isotopes used in?

A
  • Balance studies
  • Plasma appearance
  • Hb incorporation for Fe
26
Q

What are the advantages of using stable isotopes?

A
  • No known health effects
  • Can be used in any population
  • Multiple isotopes for Fe
27
Q

What are the disadvantages of using stable isotopes?

A
  • Expensive
  • More sample preparation
  • Need larger doses
  • Only 1 stable isotope for iodine so can’t study it
28
Q

What is the chemical balance method?

A

Apparent Fe absorption = Fe intake - Faecal Fe

29
Q

What are the advantages of using chemical balance?

A
  • Whole diet not single meals
  • No radiation
  • Several nutrients at once
30
Q

What are the disadvantages of using chemical balance?

A
  • Large margin of error
  • Nutrient retention may depend on status
  • No correction for endogenous excretion
31
Q

What are algorithms?

A
  • Mathematical equations
  • Use intakes of selected enhancers and inhibitors to estimate % of nutrient absorbed
  • Applied to whole diet
  • Assume a specific nutrient status
32
Q

What are the advantages of using algorithms?

A
  • Relatively quick
  • Relatively inexpensive
  • Can provide useful comparative data
33
Q

What are the disadvantages of using algorithms?

A
  • Underestimate absorption
  • Need food comp data
  • Don’t account for interactions between modifiers
  • Effects based on single meal not whole diet studies

HUNT242 (24 decks)

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