Lecture 9

Question 1

what is bioavailability

Answer 1

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

Question 2

Non-heam Fe absorption

Answer 2

~5-15%

Question 3

dietary requirements are greater than

Answer 3

losses

Question 4

ways we have losses of iron

Answer 4

epithelial cells
fluids

Question 5

Epithelial cells

Answer 5

-Skin
-Intestinal mucosal cells
-Urinary tract cells

Question 6

Fluids

Answer 6

-Blood
-Bile

Question 7

what are the factors that influence bioavailability

Answer 7

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

Question 8

how does the chemical form of nutrient affect bioavailability

Answer 8

e.g haem iron vs non haem iron

Question 9

how does the composition of the food affect bioavailability

Answer 9

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

Question 10

how does the composition of the meal affect bioavailability

Answer 10

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

Question 11

example of how nutrient status of person affects bioavailability

Answer 11

low iron stores -> increase Fe absorption

Question 12

example of how physiological status of person affects bioavailability

Answer 12

e.g pregnancy -> increased Fe absorption

Question 13

example of how amount consumed affects bioavailability

Answer 13

e.g supplements vs food

Question 14

why measure bioavailability

Answer 14

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

Question 15

what are isotpoes

Answer 15

• same number of protons
• different number of neutrons
• similar chemistry, different mass

Question 16

examples of Fe isotopes

Answer 16

Fe-55, Fe-59 …… Fe-54, Fe-56

Question 17

what are radioisotopes

Answer 17

atoms with an unstable nucleus

Question 18

what is radioactive decay -> emission of:

Answer 18

emission of alpha particles, beta particles and gamma rays

Question 19

These emissions= ionizing radiation

Answer 19

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

Question 20

what are alpha particles

Answer 20

a couple of protons and neutrons

Question 21

what are beta particles

Answer 21

either one electron or a positron

Question 22

what are gamma rays

Answer 22

electromagnetic radiation

Question 23

what is the penetrating power of alpha particles

Answer 23

low penetrating power

Question 24

what is the penetrating power of beta particles

Answer 24

more penetrating power than alpha particles

Question 25

what is the penetrating power of gamma particles

Answer 25

high penetrating power

Question 26

what is the ionisation like caused by alpha particles

Answer 26

causes high ionization

Question 27

what is the ionisation like caused by beta particles

Answer 27

not as ionizing as alpha particles

Question 28

what is the ionisation like caused by gamma particles

Answer 28

causes least ionization power

Question 29

what particles are not used for bioavailability studies and why

Answer 29

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

Question 30

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

Answer 30

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

Question 31

are gamma particles safe to use and are they pentrating

Answer 31

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

Question 32

what type of studies are radioisotopes used in

Answer 32

- balance studies (admin dose - faecal (+urine) losses - whole body counting -plasma appearance - Hb incorporation (for Fe - 14 days after dose)

Question 33

what are the advantages to radioisotopes

Answer 33

- true tracers - often cheaper than stable isotopes - minimal sample preparation needed

Question 34

what are the disadvantages to radioisotopes

Answer 34

- 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

Question 35

what are the characteristics of stable isotopes

Answer 35

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

Question 36

what types of studies are stable isotopes used in

Answer 36

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

Question 37

what are the advantages to stable isotopes

Answer 37

- 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)

Question 38

what are the disadvantages to stable isotopes

Answer 38

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

Question 39

what is another human method for measuring bioavailability

Answer 39

chemical balance apparent Fe absorption = Fe intake - Faecal Fe

Question 40

what are the advantages to chemical balance method

Answer 40

- whole diet not single meals - no radiation - several nutrients at once

Question 41

what are the disadvantages to chemical balance method

Answer 41

- large margin of error - nutrient retention may depend on status for some nutrients - no correction for endogenous excretion

Question 42

what are algorithms for bioavailability study

Answer 42

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

Question 43

algorithms for bioavailability are usually

Answer 43

applied to the whole diet, assume a specific nutrient status

Question 44

what are the advantages to using mathematical equations to measure bioavailability

Answer 44

- relatively quick - relatively inexpensive - can provide useful comparative data

Question 45

what are the disadvantages to using mathematical equations to measure bioavailability

Answer 45

- 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

Question 46

what studies provide the strongest data for bioavailability

Answer 46

studies using radioisotopes or stable isotopes

Question 47

what methods for measuring iron absorption should be treated with caution

Answer 47

algorithms estimating iron absorption