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HUNT242 > Lecture 9 > Flashcards

Lecture 9 Flashcards

Intake /= amount available to the body

1
Q

what is bioavailability

A

the proportion of a nutrient that is digested, absorbed and utilised

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2
Q

Non-heam Fe absorption

A

~5-15%

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3
Q

dietary requirements are greater than

A

losses

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4
Q

ways we have losses of iron

A

epithelial cells
fluids

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5
Q

Epithelial cells

A

-Skin
-Intestinal mucosal cells
-Urinary tract cells

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6
Q

Fluids

A

-Blood
-Bile

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7
Q

what are the factors that influence bioavailability

A
  • chemcical form of nutrient
  • composition of the food
  • composition of the meal
  • nutrient status of person
  • physiological status of person
  • amount consumed
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8
Q

how does the chemical form of nutrient affect bioavailability

A

e.g haem iron vs non haem iron

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9
Q

how does the composition of the food affect bioavailability

A

e.g meat / fish / poultry factor enhances NHFe absorption from meat

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10
Q

how does the composition of the meal affect bioavailability

A

e.g vitamin C in fruit juice enhances NHFe absorption from breakfast cereal

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11
Q

example of how nutrient status of person affects bioavailability

A

low iron stores -> increase Fe absorption

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12
Q

example of how physiological status of person affects bioavailability

A

e.g pregnancy -> increased Fe absorption

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13
Q

example of how amount consumed affects bioavailability

A

e.g supplements vs food

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14
Q

why measure bioavailability

A
  1. nutrient reference values are set using % absorption from typical diet
  2. identify and quantify new “enhancers” and “inhibitors” of nutrient absorption
  3. compare efficacy of new supplements
  4. develop algorithms to estimate absorption
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15
Q

what are isotpoes

A
  • same number of protons
  • different number of neutrons
  • similar chemistry, different mass
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16
Q

examples of Fe isotopes

A

Fe-55, Fe-59 …… Fe-54, Fe-56

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17
Q

what are radioisotopes

A

atoms with an unstable nucleus

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18
Q

what is radioactive decay -> emission of:

A

emission of alpha particles, beta particles and gamma rays

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19
Q

These emissions= ionizing radiation

A

-Remove e’s from atoms -> products damage tissues
-Risk depends on route, dose and ionisation energy

20
Q

what are alpha particles

A

a couple of protons and neutrons

21
Q

what are beta particles

A

either one electron or a positron

22
Q

what are gamma rays

A

electromagnetic radiation

23
Q

what is the penetrating power of alpha particles

A

low penetrating power

24
Q

what is the penetrating power of beta particles

A

more penetrating power than alpha particles

25
Q

what is the penetrating power of gamma particles

A

high penetrating power

26
Q

what is the ionisation like caused by alpha particles

A

causes high ionization

27
Q

what is the ionisation like caused by beta particles

A

not as ionizing as alpha particles

28
Q

what is the ionisation like caused by gamma particles

A

causes least ionization power

29
Q

what particles are not used for bioavailability studies and why

A

alpha particles as they wouldn’t get through your skin or blood to be picked up and even if they were they are really risky so wouldn’t want to use them anyway

30
Q

what is the use of beta particles like for a bioavailability study

A

there are able to pass through the skin and are much safer to use than alpha, gamma is the safest though

31
Q

are gamma particles safe to use and are they pentrating

A

you need at least 10cm of lead to stop them, so they are very penetrating, but also the safest to use for bioavailability studies

32
Q

what type of studies are radioisotopes used in

A
  • balance studies (admin dose - faecal (+urine) losses
  • whole body counting

-plasma appearance

  • Hb incorporation (for Fe - 14 days after dose)
33
Q

what are the advantages to radioisotopes

A
  • true tracers
  • often cheaper than stable isotopes
  • minimal sample preparation needed
34
Q

what are the disadvantages to radioisotopes

A
  • radiation dose (research doses ~ X ray exam or long distance flight)
  • cannot be used with pregnant or lactating women, infants or children
  • ethical approval only possible in certain countries
35
Q

what are the characteristics of stable isotopes

A

-stable nucleus, so do not emit radiation
- naturally occurring

36
Q

what types of studies are stable isotopes used in

A
  • balance studies (similar to radioisotopes) ( admin dose - faecal (+urine) losses
  • plasma appearance
  • haemoglobin incorporation
37
Q

what are the advantages to stable isotopes

A
  • no known health effects (because the isotopes are stable and naturally occurring)
  • can be used in any population (even pregnant women)
  • multiple isotopes (for Fe)
38
Q

what are the disadvantages to stable isotopes

A
  • expensive (isotopes, equipment and time)
  • more sample preparation
  • needs larger doses
  • only 1 stable isotope for iodine so cant study absorption
39
Q

what is another human method for measuring bioavailability

A

chemical balance

apparent Fe absorption = Fe intake - Faecal Fe

40
Q

what are the advantages to chemical balance method

A
  • whole diet not single meals
  • no radiation
  • several nutrients at once
41
Q

what are the disadvantages to chemical balance method

A
  • large margin of error
  • nutrient retention may depend on status for some nutrients
  • no correction for endogenous excretion
42
Q

what are algorithms for bioavailability study

A

mathematical equations that use intakes of selected enhancers and inhibitors to estimate % of nutrient absorbed

43
Q

algorithms for bioavailability are usually

A

applied to the whole diet, assume a specific nutrient status

44
Q

what are the advantages to using mathematical equations to measure bioavailability

A
  • relatively quick
  • relatively inexpensive
  • can provide useful comparative data
45
Q

what are the disadvantages to using mathematical equations to measure bioavailability

A
  • underestimate absorption
  • need food comp data for components not in FOODfiles
  • don’t account for interactions between abn modifiers
  • effects based on single meal not whole diet studies
46
Q

what studies provide the strongest data for bioavailability

A

studies using radioisotopes or stable isotopes

47
Q

what methods for measuring iron absorption should be treated with caution

A

algorithms estimating iron absorption

HUNT242 (23 decks)

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