WEEK 5 Biomarkers Flashcards
Recovery biomarkers = ?
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
Assumption recovery biomarker?
- Individuals are in a steady state; do not increase/decrease body mass (unlike young/old/ pregnant)
- compound recovers almost completely/completely
To what are recovery markers sensitive?
To diseases that affect their excretion (kidney)
Predictive biomarkers = ? Absolute intake?
Incomplete recovery, but stable and time-dependent correlation with intake.
> Allow an estimation of absolute intake, but not as reliable as recovery markers
Which predictive biomarker is the only one available now?
Urinary sucrose
Concentration biomarkers = ?
- 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
Adv conc. biomarkers?
can be measured in almost all specimens available
Disadv conc. biomarkers?
only different levels of intake, instead of absolute dietary intake
What do concentration biomarkers take into account?
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
Functional markers?
measure the physiological effect of specific foods as a surrogate marker of intake. (e.g. measures B12)
What biomarker to use for carbohydrate intake?
- currently no biomarker for the intake of total carbohydrates except for sucrose -
How to assess protein intake?
By total urinary nitrogen
What assumption for measuring total urinary nitrogen?
based on assumption that subjects are in N- balance, neither accumulation/loss due to growth, starvation, diet or injury
What aspects to think about when measuring total N intake?
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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
What is the kjieldahl method?
All N in sample > converted to ammonium sulphate > analysed.
What are advantages of the kjieldahl method?
Determines not only protein nitrogen, but all organic nitrogen present in the sample
very robust and reproducible, for many experiments
Disadv kjieldahl method?
Only provides information on total protein intake, not intake of specific amino acids or the source of protein
How is fat intake measured?
By measuring individual fatty acids. The fatty acid composition = used to make inferences regarding dietary fat intake.
What are the main fatty acids?
- Fatty acids mainly triacylglycerol, phospholipids and cholesterol esters
Where are the main fatty acids found?
Found in membranes, adipose tissue and also plasma (as free fatty acids). They undergo extensive metabolism
What is mainly used to make inferences on intake?
Fatty acid profile, because distribution mainly depends on type of fatty acid.
IS transport of fatty acids into adipose tissue presumed to be selective?
No, non-selective, but might not be for all tissues
What is the half-life of adipose tissue?
1-2 years
What is the half-life of erythrocytes?
half-life of 60 days. Erythrocyte membrane fatty acids more suitable to assess medium-term diet.
By what technique is fatty acid analysis mostly performed?
TLC, thin layer chromatography
Why is there no biomarker on carbohydrate intake?
, partially due to the complex nature of these nutrients and their extensive metabolism
Urinary sugar intake biomarker: when predictive/concentration? How is it determined?
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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
Fibre/wholegrain biomarker = alkylredorcinols. Alternative biomarkers?
- stool weight, which correlates well with fibre intake (r=0.8)
- faecal hemicellulose, which also shows a good correlation
How to use biomarkers for micronutrients?
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
Caratenoids: characteristics?
- 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
Flavonoids: characteristics?
- 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
Vit C: characteristic as biomarker?
- most commonly used biomarker of fruit and vegetable intake
Meat & fish biomarker?
- 1-methyl-histidine proposed biomarker
- ratio of stable carbon and nitrogen
- The urinary isotope ratio for short-term dietary intake
