Medical Biochemistry Card 2 Item 1 [part 2]

Food & Nutrition, Vitamins
&
Minerals

The Dietary Reference Intakes (DRIs)
provide estimates of the amounts
of nutrients required to prevent
deficiencies and maintain optimal
health and growth.

The DRIs consist of
four
dietary reference
standards

The DRIs are designated for specific
age
physiologic states
&
gender group

Four
Dietary reference
standards-

1. Estimated Average Requirement
2. Recommended Dietary Allowance
3. Adequate Intake
4. Tolerable Upper Intake Level

1. Estimated Average
Requirement
(EAR)

The average
daily nutrient intake level
estimated to meet the
requirement of
one half (50%) of the
healthy individuals

It is useful in estimating the
actual requirements in
groups and individuals.

The EAR serves as the
foundation for setting the
RDA.

2. Recommended Dietary
Allowance
(RDA)

The RDA is the average
daily dietary intake level
that is sufficient to meet the
nutrient requirements of
nearly all individuals (97%–98%)
in a life stage and gender group.

RDA can meet the
nutrient requirements
of nearly all individuals.

It is not the
minimal requirement for
healthy individuals but
it provides a margin of
safety
for most individuals.

Several factors influence on RDA-
 Age
 Sex
 Pregnancy & lactation
 Illness
 Massive injury
 Major surgery

An Adequate Intake is set instead
of an RDA if sufficient
scientific evidence
is not available to calculate an
EAR or RDA.

The AI is based on estimates of
nutrient intake by a group of
apparently
healthy people.

For example,
the AI for young infants, for whom
human milk is the recommended sole
source of food for the first 4–6 months.
is based on the estimated
daily mean nutrient intake
supplied by human milk for
healthy, full-term infants who are
exclusively breastfed.

4. Tolerable Upper Intake
Level
( UL)

The highest average
daily nutrient intake level that is
likely to pose no risk of
adverse health effects
to almost all individuals in the general
population.

As intake increases
above the UL, the
potential risk of
adverse effects
may increase.

As for example,
Excessive intake of fat soluble
vitamins may cause
toxicity.
Vitamin A
may lead to
Hepatomegaly

Effects of hyper vitaminosis A
Dermatitis Alopecia
Intracranial pressure

Metabolic rate (MR) is the
energy liberated per unit time
in the body.

The metabolic rate
varies between
individuals.

It is 1.2kcal/min at rest in
standard temperature and
pressure.

A normal adult utilizes about
250ml (0.25L) oxygen
per minute at rest.

When 1L oxygen is consumed in
oxidative process in a normal adult
person on mixed diet, it is the energy
equivalent of oxygen.
It is about 4.8 kcal/L of oxygen
consumption

Factors affecting metabolic rate
BMR (Basal Metabolic Rate)
SDA (Specific Dynamic Action of
food)
Physical activity

Atmospheric temperature
Emotional state
Pregnancy & lactation

Humans generate
energy by
metabolism of the
macronutrients.

ATP is the energy currency of cell

ATP is used for
three
energy requiring
processes

1.Basal metabolic rate (BMR)
2.Specific dynamic action of
food (SDA)
3.Physical activity of the body

Growth,
Pregnancy & lactation
needs additional
energy supply.

1. Basal metabolic rate
(BMR)
or

Resting metabolic rate
(RMR)
It is in recent use for
BMR

The minimum amount of energy
required by the body to maintain life at
complete physical & mental rest,
in the post absorptive state &
in a comfortable surrounding .

BMR represents the energy
required to carry out the
normal body
functions
at basal conditions.

In basal conditions,
body appears to be
at total rest
But....

several functions
within the body
continuously occur

such as -
a. Respiration
b. Working of heart
c. Conduction of nerve impulse
d. Reabsorption by renal tubules

e. Gastrointestinal motility
f. Blood flow
g. Ion transport
h. Maintenance of cellular
integrity

Na+-K+ Pump
consumes
50% of
basal energy

Basal conditions:
 The subjects should be at rest.
 He or she should be awake.
 The environment should be warm
(250C).

 No strenuous exercise after the
night of restful sleep.
 12 hours after the last meal.

Normal values of BMR
Adult male Adult female
35-38 cal/sq.m/hour 32-35 cal/sq.m/hour

1. Body surface area:
BMR is directly proportional to the
body surface area.
Surface area is related to the weight
& height.

2. Sex :
Men have higher BMR than women
(5%) due to higher proportion of
lean muscle mass.

3. Age:
In infants & growing children,
the BMR is higher .

In adults,
BMR decreases about 2%
per decade of life.

4. Physical activity:
BMR is increased in persons with
regular exercise .

5. Hormones :
Some hormones
increase BMR .

Thyroid hormones (T3 & T4)
increase the rate of
metabolism & also
BMR

5. Hormones :
Other hormones increase BMR -
Thyroid hormones
Epinephrine
Cortisol
Growth hormone
Sex hormones

6. Environment:
In too cold climate –
the BMR is higher

7. Starvation :
During the period of starvation ,
BMR decreases up to 50%.

8. Fever :
Fever causes an increase in
BMR.

An elevation by >10% in
BMR is observed for
every 1ᵒC rise in
body temperature.

9. Disease states :
BMR increase in
Hypertension

10. Racial variation :
Eskimos - higher BMR.

11. Pregnancy :
BMR increases
during pregnancy

1. BMR is important to calculate
the calorie requirement
of an individual &
planning of diets.

2. Determinants of BMR is useful for
the assessment of
thyroid functions & some other
pathological conditions .
Thyroid gland

Specific dynamic action of food
SDA

The specific dynamic action of
food (SDA) is the extra
heat production,
over & above the calculated
calorie value when a
given food is metabolized by
the body .

SDA is the diet induced
thermogenesis

It is also known as
calorigenic or
thermogenic action
of food .

SDA of different foods:
Protein 30%
Fat 13%
Carbohydrate 5%
Mixed diet 10%

For example,
For a food containing
25 g of protein , the heat production
is 100 kcal (4×25) , but practically
the energy released is about
130 kcal because the SDA of protein
is about 30%.

The energy required by SDA is
provided from the
energy reserve or
store of the body .

It is utilized by the following
processes –
a. Digestion of food
b. Absorption & transport of the
product of digestion.
c. Metabolism &
d. Storage of food.
e.g.- Glycogen, depot fat etc.

The SDA of protein is to meet
the energy requirements for –
Oxidative deamination
Synthesis of urea
Synthesis of protein etc.

The SDA of carbohydrate is due
to the energy expenditure &
for the conversion of glucose
to glycogen &

The SDA of fat is due to the
energy expenditure for
storage , mobilization &
oxidation of fat .

Significance of SDA :
For the utilization of food
(Digestion, absorption, metabolism
& storage) by the body, some
energy is consumed from the body
stores .

SDA is actually an energy
expenditure by the body for the
utilization of foodstuffs.

SDA is used for calculation of energy
demand &
planning of the diet for an
individual.

So, in an additional ,
10% calories
should be added to the
total energy need of the body.

Body mass index (BMI):
The body mass index is a measure of
relative weight adjusted for height .
This allows comparisons both within &
between populations . The BMI is calculated
as follows-
BMI = (Weight in Kg ) / ( Height in meters)2

The BMI is calculated as follows-
BMI = (Weight in Kg ) / ( Height in meters)2

The Uses of BMI
BMI can help to
determine
probable health
risks if it's
outside of the
healthy range.

Higher BMI increases risk of:
Insulin resistance
Type 2 diabetes
Hypertension
Stroke
Dyslipidemia
Coronary heart disease
Gallbladder disease
Certain cancers

Categories of BMI
Status
Under
Nutri-
tion
Normal
Over
weight
Obese
Extre -
me
obese
BMI < 18.5
18.5 -
24.9
25-29.9 ≥ 30 > 40

Medical Biochemistry Card 2 Item 1 [part 2]

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Medical Biochemistry Card 2 Item 1 [part 2]