WEEK 5 Biomarkers

Question 1

Recovery biomarkers = ?

Answer 1

based on compounds that can be recovered completely – or almost completely – following consumption, mainly in 24-hour urine samples

well-known relationship with intake and this relationship is consistent between individuals, with low inter-individual variability

Question 2

Assumption recovery biomarker?

Answer 2

• Individuals are in a steady state; do not increase/decrease body mass (unlike young/old/ pregnant)
• compound recovers almost completely/completely

Question 3

To what are recovery markers sensitive?

Answer 3

To diseases that affect their excretion (kidney)

Question 4

Predictive biomarkers = ? Absolute intake?

Answer 4

Incomplete recovery, but stable and time-dependent correlation with intake.
> Allow an estimation of absolute intake, but not as reliable as recovery markers

Question 5

Which predictive biomarker is the only one available now?

Answer 5

Urinary sucrose

Question 6

Concentration biomarkers = ?

Answer 6

• this relationship is less well known and more variable, with very high inter-individual variability
• most common type
• Used to investigate diet and disease risk

Question 7

Adv conc. biomarkers?

Answer 7

can be measured in almost all specimens available

Question 8

Disadv conc. biomarkers?

Answer 8

only different levels of intake, instead of absolute dietary intake

Question 9

What do concentration biomarkers take into account?

Answer 9

Biomarker concentration determined in blood/urine takes into account bioavailability, metabolism, nutrient–nutrient interaction and excretion
- > therefore might provide better information on the bioavailable nutrient than dietary data

Question 10

Functional markers?

Answer 10

measure the physiological effect of specific foods as a surrogate marker of intake. (e.g. measures B12)

Question 11

What biomarker to use for carbohydrate intake?

Answer 11

• currently no biomarker for the intake of total carbohydrates except for sucrose -

Question 12

How to assess protein intake?

Answer 12

By total urinary nitrogen

Question 13

What assumption for measuring total urinary nitrogen?

Answer 13

based on assumption that subjects are in N- balance, neither accumulation/loss due to growth, starvation, diet or injury

Question 14

What aspects to think about when measuring total N intake?

Answer 14

>

On average on 80% of dietary intake
Daily individual variations require the collection of urine samples on several days
Collection of 24-hour urine samples

Question 15

What is the kjieldahl method?

Answer 15

All N in sample > converted to ammonium sulphate > analysed.

Question 16

What are advantages of the kjieldahl method?

Answer 16

Determines not only protein nitrogen, but all organic nitrogen present in the sample

very robust and reproducible, for many experiments

Question 17

Disadv kjieldahl method?

Answer 17

Only provides information on total protein intake, not intake of specific amino acids or the source of protein

Question 18

How is fat intake measured?

Answer 18

By measuring individual fatty acids. The fatty acid composition = used to make inferences regarding dietary fat intake.

Question 19

What are the main fatty acids?

Answer 19

• Fatty acids mainly triacylglycerol, phospholipids and cholesterol esters

Question 20

Where are the main fatty acids found?

Answer 20

Found in membranes, adipose tissue and also plasma (as free fatty acids). They undergo extensive metabolism

Question 21

What is mainly used to make inferences on intake?

Answer 21

Fatty acid profile, because distribution mainly depends on type of fatty acid.

Question 22

IS transport of fatty acids into adipose tissue presumed to be selective?

Answer 22

No, non-selective, but might not be for all tissues

Question 23

What is the half-life of adipose tissue?

Answer 23

1-2 years

Question 24

What is the half-life of erythrocytes?

Answer 24

half-life of 60 days. Erythrocyte membrane fatty acids more suitable to assess medium-term diet.

Question 25

By what technique is fatty acid analysis mostly performed?

Answer 25

TLC, thin layer chromatography

Question 26

Why is there no biomarker on carbohydrate intake?

Answer 26

, partially due to the complex nature of these nutrients and their extensive metabolism

Question 27

Urinary sugar intake biomarker: when predictive/concentration? How is it determined?

Answer 27

>

Predictive when determined in 24-hour urine, concentration biomarkers when determined in spot urine samples
Traditionally determined using enzymatic assays. Alternatively, urinary sugars can be analysed by chromatographic methods

Question 28

Fibre/wholegrain biomarker = alkylredorcinols. Alternative biomarkers?

Answer 28

• stool weight, which correlates well with fibre intake (r=0.8)
• faecal hemicellulose, which also shows a good correlation

Question 29

How to use biomarkers for micronutrients?

Answer 29

Many micronutrients can be used as their own biomarker of intake.
Mostly concentration biomarkers, – with the exception of potassium and to some extent sodium – as concentration is affected by factors

Question 30

Caratenoids: characteristics?

Answer 30

• Synthesized by photosynthetic organisms
• 10% can be converted to vit. A (carotenoid status = different from vit. A status)
• Absorption affected by fat content in food, colonic metabolism, hormonal factors

Question 31

Flavonoids: characteristics?

Answer 31

• Secondary plant metabolites
• Flavonoids can be found in most plant-based foods, but composition is very variable
• Used as summary fruit & veg intake, identify specific food groups or individual foods

Question 32

Vit C: characteristic as biomarker?

Answer 32

• most commonly used biomarker of fruit and vegetable intake

Question 33

Meat & fish biomarker?

Answer 33

• 1-methyl-histidine proposed biomarker
• ratio of stable carbon and nitrogen
• The urinary isotope ratio for short-term dietary intake