Lecture 9 - Intake / Amount Available to the Body

Question 1

what is bioavailability

Answer 1

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

Question 2

dietary requirements are greater than

Answer 2

losses

Question 3

ways we have losses of iron

Answer 3

• epithelial cells
• fluids

Question 4

what are the factors that influence bioavailability

Answer 4

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

Question 5

how does the chemical form of nutrient affect bioavailability

Answer 5

e.g haem iron vs non haem iron

Question 6

how does the composition of the food affect bioavailability

Answer 6

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

Question 7

how does the composition of the meal affect bioavailability

Answer 7

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

Question 8

example of how nutrient status of persom affects bioavailability

Answer 8

low iron stores > increase Fe absorption

Question 9

example of how physiological status of person affects bioavailability

Answer 9

e.g pregnancy > increased Fe absorption

Question 10

example of how amount consumed affects bioavailability

Answer 10

e.g supplements vs food

Question 11

why measure bioavailability

Answer 11

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 12

what are isotpoes

Answer 12

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

Question 13

examples of Fe isotopes

Answer 13

Fe-55, Fe-59 …… Fe-54, Fe-56

Question 14

what are radioisotopes

Answer 14

atoms with an unstable nucleus

Question 15

what is radioactive decay

Answer 15

emission of alpha particles, beta particles and gama rays

Question 16

what are alpha particles

Answer 16

a couple of protons and neutrons

Question 17

what are beta particles

Answer 17

either one electron or a positron

Question 18

what are gamma rays

Answer 18

electromagnetic radiation

Question 19

emissions of radioactive decay are

Answer 19

ionizing radiations

Question 20

what are ionizing radiations

Answer 20

removes electrons from atoms > products damage tissues

Question 21

what is the penetrating power of alpha particles

Answer 21

low penetrating power

Question 22

what is the penetrating power of beta particles

Answer 22

more penetrating power than alpha particles

Question 23

what is the penetrating power of gamma particles

Answer 23

high penetrating power

Question 24

what is the ionisation like caused by alpha particles

Answer 24

causes high ionization

Question 25

what is the ionisation like caused by beta particles

Answer 25

not as ionizing as alpha particles

Question 26

what is the ionisation like caused by gamma particles

Answer 26

causes least ionization power

Question 27

what particles are not used for bioavailability studies and why

Answer 27

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 28

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

Answer 28

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

Question 29

are gamma particles safe to use and are they pentrating

Answer 29

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 30

what type of studies are radioisotopes used in

Answer 30

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

Question 31

what are the advantages to radioisotopes

Answer 31

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

Question 32

what are the disadvantages to radioisotopes

Answer 32

- 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 33

what are the characteristics of stable isotopes

Answer 33

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

Question 34

what types of studies are stable isotopes used in

Answer 34

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

Question 35

what are the advantages to stable isotopes

Answer 35

- 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 36

what are the disadvantages to stable isotopes

Answer 36

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

Question 37

what is another human method for measuring bioavailability

Answer 37

chemical balance apparent Fe absorption = Fe intake - Faecal Fe

Question 38

what are the advantages to chemical balance method

Answer 38

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

Question 39

what are the disadvantages to chemical balance method

Answer 39

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

Question 40

what are algorithms for bioavailability study

Answer 40

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

Question 41

algorithms for bioavailability are usually

Answer 41

applied to the whole diet, assume a specific nutrient status

Question 42

what are the advantages to using mathematical equations to measure bioavailability

Answer 42

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

Question 43

what are the disadvantages to using mathematical equations to measure bioavailability

Answer 43

- 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 44

what studies provide the strongest data for bioavailability

Answer 44

studies using radioisotopes or stable isotopes

Question 45

what methods for measuring iron absorption should be treated with caution

Answer 45

algorithms estimating iron absorption