Lecture 9: Intake vs. Amount Available to the Body

Question 1

What is bioavailability?

Answer 1

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

Question 2

What is the absorption of non-haem iron?

Answer 2

approx. 5-15%

Question 3

How is iron in the body?

Answer 3

Through epithelial cells and fluids

Question 4

How is iron lost in epithelial cells?

Answer 4

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

Question 5

How is iron lost in fluids?

Answer 5

• Blood (gut 0.4mg)
• Menstruation
• Bile (0.2mg)

Question 6

What are the dietary requirements of iron?

Answer 6

Men: 8mg
Women: 18mg

Question 7

What are the average iron losses per day?

Answer 7

Men: 1mg
Women: 2mg

Question 8

What is bioavailability influenced by?

Answer 8

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

Question 9

What happens when someone has low iron stores?

Answer 9

Increased Fe absorption

Question 10

What happens to iron absorption when someone is pregnant?

Answer 10

It increases

Question 11

Why do we measure bioavailability?

Answer 11

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

Question 12

What are isotopes?

Answer 12

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

Question 13

What are the three components of an atom?

Answer 13

• Protons (+)
• Neutrons (0)
• Electrons (-)

Question 14

What are isotopes of Fe?

Answer 14

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

Question 15

What are radioisotopes?

Answer 15

Atoms with an unstable nucleus that emit radioactive decay

Question 16

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

Answer 16

• Alpha particles
• Beta particles
• Gamma rays

Question 17

How does ionising radiation work?

Answer 17

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

Question 18

What are the characteristics of alpha particles?

Answer 18

• Low penetrating power
• Cause high ionisation power

Question 19

What are the characteristics of beta particles?

Answer 19

• More penetrating than alpha
• Not as ionising as alpha

Question 20

What are the characteristics of gamma particles?

Answer 20

• High penetrating power
• Causes least ionisation

Question 21

What types of studies use radioisotopes?

Answer 21

• Balance studies
• Whole body counting
• Plasma appearance
• Hb incorporation

Question 22

What are the advantages of using radioisotopes?

Answer 22

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

Question 23

What are the disadvantages of using radioisotopes?

Answer 23

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

Question 24

What are stable isotopes?

Answer 24

• Stable nucleus so do not emit radiation
• Naturally occuring

Question 25

What type of studies are stable isotopes used in?

Answer 25

- Balance studies - Plasma appearance - Hb incorporation for Fe

Question 26

What are the advantages of using stable isotopes?

Answer 26

- No known health effects - Can be used in any population - Multiple isotopes for Fe

Question 27

What are the disadvantages of using stable isotopes?

Answer 27

- Expensive - More sample preparation - Need larger doses - Only 1 stable isotope for iodine so can't study it

Question 28

What is the chemical balance method?

Answer 28

Apparent Fe absorption = Fe intake - Faecal Fe

Question 29

What are the advantages of using chemical balance?

Answer 29

- Whole diet not single meals - No radiation - Several nutrients at once

Question 30

What are the disadvantages of using chemical balance?

Answer 30

- Large margin of error - Nutrient retention may depend on status - No correction for endogenous excretion

Question 31

What are algorithms?

Answer 31

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

Question 32

What are the advantages of using algorithms?

Answer 32

- Relatively quick - Relatively inexpensive - Can provide useful comparative data

Question 33

What are the disadvantages of using algorithms?

Answer 33

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