Video summary
Biomarkers serve as measurable biological indicators found in tissues, fluids, or excreta that objectively reflect dietary intake, nutritional status, and metabolism, offering a crucial alternative to self-reported methods like food frequency questionnaires. Unlike traditional assessments which are often plagued by recall bias, social desirability bias, and misreporting of portion sizes, biomarkers provide independent evidence that reduces reliance on participant memory or honesty. Common samples used for these markers include blood serum or plasma, urine, hair, nails, saliva, adipose tissue, and feces. In nutritional epidemiology, they play a vital role by validating dietary tools, estimating true intake, identifying nutrient deficiencies, and strengthening the correlation between diet and disease outcomes.
Biomarkers are generally categorized into three main types based on their physiological basis and application: recovery, concentration, and predictive biomarkers. Recovery biomarkers, such as doubly labeled water for energy expenditure or 24-hour urinary nitrogen for protein intake, provide quantitative estimates of actual intake by relying on direct physiological relationships between consumption and excretion; however, they are often expensive and require strict collection protocols. Concentration biomarkers measure the level of specific nutrients in biological fluids, like serum vitamins or blood lipids, which indicate exposure but are influenced by individual factors such as absorption rates and metabolism, preventing them from giving an absolute measure of intake. Predictive biomarkers, exemplified by urinary sugars for total sugar intake, use calibration equations derived from controlled feeding studies to estimate intake and are particularly useful for analyzing dose-response relationships in large-scale epidemiological studies.
While biomarkers significantly improve the accuracy and validity of dietary assessments by detecting underreporting common in obese individuals or those with hidden salt consumption in processed foods, they face several limitations including high costs, specialized laboratory requirements, and biological variability influenced by genetics and disease states. Certain markers also lack specificity, as a single nutrient indicator like serum carotenoids can reflect intake from various food sources such as carrots, tomatoes, and spinach, while others have short half-lives that only capture recent dietary habits rather than long-term patterns. Additionally, the invasive nature of sample collection can lead to ethical concerns and higher dropout rates in studies. Despite these challenges, when combined with traditional self-report methods, biomarkers offer a more comprehensive and reliable evaluation of the complex relationship between diet and health, ultimately providing a clearer picture of true biological outcomes rather than estimated consumption.
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Hello and welcome to your learners to
the NPTEL course on nutrition
epidemiology a way towards a healthy
life.
For the module 3 dietary assessment
nutritional status and measurement error
for the chapter 29, we'll be studying
about biomarkers in dietary assessment.
So what are biomarkers? The types of
biomarkers, biomarkers of intake and
biomarkers of status.
Advantages over self-report methods.
Limitations and cost issues and case
discussion for the biomarkers.
So what are biomarkers?
A biomarker is a measurable biological
indicator
found in the body tissue,
fluids or excreta
that reflects a dietary intake, nutrient
exposure,
nutritional status and metabolism or a
disease risk.
So with this you can understand how
biomarker is important as a biological
indicator.
According to the nutritional
epidemiology,
biomarkers provide objective measures
of dietary exposure and nutritional
status
reducing the reliance on self-reported
dietary information.
So there is an objective component over
here which is very important to state
that whatever is being reported will be
giving you an exact information.
Common biological samples used for the
biomarkers are blood
where you can get a serum,
plasma, or whole blood.
The second is urine,
hairs, and nails.
Also, saliva, adipose tissue, and feces.
So, why are biomarkers important?
In the traditional dietary assessment
methods, such as 24-hour dietary calls,
food records, food frequency
questionnaires, and diet histories are
vulnerable to recall bias, where the
memory is very important.
Social disability biases are there,
which is very difficult to overcome.
Misreporting is very common,
and portion size estimate errors are
something which are very redundant.
Day-to-day dietary variations are very
common in countries like India.
So, biomarkers provide independent
evidence of intake,
and can improve dietary assessment
accuracy, which is a need.
So, you can say that biomarkers are
objective, accurate, and independent
measure of intake and status.
What is the role of biomarkers in
nutritional epidemiology?
You can understand it validates the
dietary assessment tools.
It estimates the true dietary intake,
and biomarkers are used to assess
nutrition status.
They identify nutrient deficiencies,
which is a peculiarity of biomarkers.
They also study diet-disease
relationship.
Also, biomarkers correct measurement
errors in epidemiological studies.
So, you can understand the whole set of
advantages that biomarkers are there in
nutritional epidemiology.
Biomarkers provide objective,
reliable, and valid information.
They strengthen the dietary assessment
and helps understand the links between
diet, nutrition, and health.
So, there is a correlation which is made
more stronger with the help of
biomarkers.
What are the type of biomarkers?
So, you can say recovery biomarkers,
concentration biomarkers, and predictive
biomarkers.
These are the major three types.
In the recovery biomarkers, you can
understand that they provide
quantitative estimates of actual intake.
Because the intake and excretion are
directly related according to the
physiological principles.
As you understand from the knowledge of
physiology, the biomarkers are
considered the gold standard biomarkers
who gives us
only a few recovery biomarkers
are known as making the pressure about
reference measures.
So, on physiological standards, they are
being proved.
The characteristics comes that they are
highly accurate.
They direct proportional between the
intake and the biomarker level.
So, you can say they have a very
quantitative estimate.
They're independent of self-report bias,
which is very common in the other
methods.
>> [snorts]
>> And recovery biomarkers can be used as a
reference measure to assess and correct
for errors.
Lot of underreporting is overcome over
here,
which is very common in self-reported
dietary data.
Now, we will take the examples of
recovery biomarkers.
Doubly labeled water, DLW,
measures average energy expenditure over
a 2-weeks period
used as a marker of energy intake for a
weight stable individual.
A weight stable individual is there
where you can see a
average expenditure of water is being
taken, H2O.
The Why it is being done?
The individual consume water labeled
with stable
isotopes uh deuterium and oxygen. So,
these isotopes disappear from the body
at different rates.
The differences reflect carbon dioxide
production, which is used to estimate
energy expenditure.
Under weight stable condition, energy
intake is equal to energy expenditure.
What is the application? The application
is validation of energy intake,
assessment of underreporting, and
calibration studies.
Second example is 24-hour urinary
nitrogen.
What are the measures? Protein intake.
Approximately 80 to 90% of the dietary
nitrogen is excreted in urine.
Thus, 24-hour urinary nitrogen can
estimate actual protein intake.
What are the advantages?
Advantages are high accuracy
and strong physiological
basis.
But,
with this, there are some limitations.
It is very expensive.
Participant burden is more, and it
requires a complete urine collection for
24 hours.
So, with these two examples, you can
understand how recovery biomarkers make
their place.
Concentration biomarkers.
These are the most common types of
biomarkers that are used, and they
measure the concentration of specific
chemical or nutrient in the biological
fluids.
Biological fluids like blood, urine,
adipose tissue.
They indicate an exposure, but they are
not direct quantitative measure of
intake, just like the recovery
biomarkers.
The concentration biomarkers are highly
correlated with intake, but are heavily
influenced by individual factors.
The individual factors may be
absorption, metabolism, genetics, and
disease states.
These are all the physiological
condition which derives to give this
variation.
Concentration biomarkers cannot provide
an absolute measure of intake. You
cannot say X mg/mL equals to Y g C. It
is not possible.
It cannot assess the error of
self-reported intakes in a validation
studies.
But, they are useful for assessing the
relationship between a tissue's
concentration and a health outcome.
Now, you can take the example of serum
vitamins.
Example, serum vitamin C or folate and
its relation to the disease condition.
Example, blood lipids, cholesterol, or
triglycerides,
or serum carotenoids from vegetables
intake. The third is predictive
biomarkers. Predictive biomarkers
estimate dietary intake through
calibration equation.
They derive from the controlled feeding
studies.
So, you can take 24 hours urine fructose
and sucrose as a marker for total
dietary sugar intake.
The predictive biomarkers are objective,
sensitive, and stable, and
time-dependent. These are the very four
important characteristics.
They are useful in larger
epidemiological studies.
They require validation equations.
It also shows that the predictive
biomarkers has a dose-response
relationship with the intake.
So, you can understand with respect to
dose, if you have to calculate, it is
very useful to use this.
It also helps in reporting errors.
So, you can say there are many important
relationship, dose-response
relationship, objectivity, sensitivity,
stableness, validity, and helpful.
So, it takes a major role to state that
predictive biomarkers are also
important.
So, these biomarkers reflect exposure in
the body, but they are affected by many
internal factors, and thus do not
provide a direct quantitative measure,
which is ideally found in the recovery
biomarkers.
What is the comparison?
You can have the comparison like
recovery, concentration, and predictive.
Out of all these three, you can say
cost-wise, recovery biomarkers are very
costly.
Concentration are moderate, and even
predictive are moderate.
The physiological bio basis,
recovery biomarkers are strong, and
along with that predictive biomarkers,
where versus the concentration
biomarkers is moderate.
Validation standard, recovery biomarkers
are gold standard, and the other two
have moderate to good in terms of taking
the standardness.
Measurement absolute intake is very yes,
as being seen in recovery biomarkers,
where work is the other concentration
productivity is known to approximate.
The example of recovery biomarkers is
DLW and urinary nitrogen.
Concentration biomarkers, it is serum
vitamins. And in productive biomarkers,
it is urinary sugar.
Biomarkers of intake and biomarkers of
status.
So, you can understand biomarkers of
intake is indicators that reflect recent
or habitual consumption of food or
nutrients before the body's homeostatic
mechanism heavily alter.
Example, salt intake 24-hour serum
sodium.
Protein intake like 24-hour urine
nitrogen or fat intake showing the
plasma fatty acids.
Plasma carotenoids by fruits and
vegetable intake. Urinary sucrose and
fructose by sugar intake. And
alkylresorcinols
by whole grain intake. So, you can
understand that nutrient foods and
biomarkers has a sort of a relationship
where energy, doubly labeled water,
protein, 24-hour urine nutrition, salt,
24-hour urine sodium, and so on with
potassium, fish, fruits, vegetables,
sugar, and whole grains are being also
being stated again.
Now, biomarkers of nutritional status.
These indicators reflect the body
nutrient stores of physiological
sufficiency.
Biomarkers are used to identify
nutrition adequacy.
They have a certain sets of things to
state that non-recovery or productive
biomarkers can be highly informative for
assessing nutrition status.
Example, vitamin D status of coming with
serum 25-hydroxyvitamin
D.
Or iodine status by urinary iodine.
vitamin B status by serum B12,
folate status by RBC folate, or serum
ferritin by iron status.
Additional biomarkers like hemoglobin,
transferrin, soluble transferrin
receptors.
So, these are enlisted to state that how
biomarkers of nutritional status comes
as an important
advantages of over self-reported
methods.
So, biomarkers are not dependent on
memory, literacy, or honesty.
They are being as a biomarkers as a
result of objectivity.
The reduced bias of recalling,
interviewing bias, and social disability
are being accumulated over here.
Detection of misreporting.
So, the biomarkers can identify
underreporting and overreporting.
Example
where
biomarkers underreporting is higher
and overreporting in biomarkers
is also lesser.
Underreporting of energy intake is
commonly observed in obese individuals.
You may have an advantage of biomarkers
improved validity.
Better self-assessment of long-term
exposures if some biomarkers reflect in
adipose tissue fats or hair minerals and
erythrocyte fatty acids.
Also, they are useful in large cohort
studies
which gives an association between diet
and disease.
They are also being seen that
self-report requires translation via
database and may contain outdated or
geographically inaccurate nutrient
values. So, biomarkers measure the
actual biological outcomes.
Food intake, food consumption, and
estimated intake. So, all these
self-report pathway is completed over
here. Whereas in biomarkers pathway, you
may have a biological sample or very
objectively biological marker analysis
is done by the instrument machine and
actual biological outcome is being
stated, which is much more clearer and
more objective.
What are the limitations of the
biomarker? Biological variability
may be influenced by genetics, disease,
age, sex, and metabolism.
Lack of specificity with respect to some
biomarkers may reflect multiple dietary
sources.
Serum carotenoids may be coming from
carrots, tomatoes, watermelon, pumpkin,
and even from spinach. Short half-life.
Certain biomarkers reflect only recent
intake.
For example, urinary sodium in 24 to 48
hours.
Sample collection burden. It requires
blood and urine collection and
laboratory processing.
Also, there are limitations of storage
requirements.
Ethical issues which gives invasive
procedures and participant has to go
with consent, compliance, and increased
dropout rates.
Higher cost also adds as a limitation.
And comparatively, if you take about the
cost of dietary assessment methods, FFQ,
the cost is low.
24-hour recall, it is moderate. Serum
vitamin assays are moderate. Urinary
biomarkers, moderate to high. And doubly
labeled water is very, very high.
Now, we will go for a case discussion.
A case study on validation of sodium
intake assessment.
In this case study, the research
question was, can a food frequency
questionnaire accurately estimate salt
intake among the adults. Very important.
The study design was taking participants
250 adults.
So, they can understand the difference
FFQ assessment of salt intake and
24-hour urinary sodium collection.
One is a biomarker, the other is an FFQ
self-assessment of salt intake.
The finding shows that the FFQ estimated
7.2 g per day salt.
Where versus the urinary sodium estimate
showed that 10.1 g per day salt.
What is the difference? The FFQ
underestimated intake by approximately
29%.
You can identify over here that the FFQ
7.2 and for urinary sodium it is 10.1.
The interpretation was that hidden salt
in processed food is more,
poor recalls for the 24 hours
part which is in FFQ,
and difficulty estimating added salt.
The conclusion of this case study is
24-hour urinary sodium provided a more
objective estimate
of the true intake. Where versus the
study also states that in comparison to
the FFQ assessment, it demonstrated the
importance of biomarkers for validating
the dietary assessment method.
So, if you take the self-reported FFQ
versus biomarkers, the more accuracy
comes more towards the biomarkers.
In the summary to this chapter, I would
like to state that biomarkers are
objective biological measures, and they
are found in blood, urine, tissue, or
other body fluids
that provide information about dietary
intake and nutritional status.
Biomarkers help overcome limitations of
self-reported dietary assessment methods
such as recall bias and underreporting.
Biomarkers can be classified on
recovery, concentration, and predictive
biomarkers.
Each serving differs different purposes
in nutritional epidemiology.
Example, doubly labeled water for energy
intake, urinary sodium for salt intake,
and serum ferritin for iron status.
So, you can understand how it is very
different for the purposes in the
nutrition epidemiology.
Although otherwise, the biomarkers
improve the accuracy and validity of
dietary assessment.
Therefore, their use is often limited
because of high cost,
specialized laboratory requirements, and
biological variability.
So, when combined and with the
traditional dietary assessment method,
biomarkers offer a more comprehensive,
more reliable evaluation of diet and
health relationship.
So, with this, we have come an end to
this chapter. You can take the help of
these references,
which are very useful for you to
understand this topic more in detail.
And thank you. Thank you for the day.
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